Permission Manager in Open Event API Server

Open Event API Server uses different decorators to control permissions for different access levels as discussed here. Next challenging thing for permissions was reducing redundancy and ensuring permission decorators are independent of different API views. They should not look to the view for which they are checking the permission or some different logic for different views.

In API Server, we have different endpoints that leads to same Resource this way we maintain relationships between different entities but this leads to a problem where permission decorators has to work on different API endpoints that points to different or same resource and but to check a permission some attributes are required and one or more endpoints may not provide all attributes required to check a permission.

For instance, PATCH /session/id` request requires permissions of a Co-Organizer and permission decorator for this requires two things, user detail and event details. It is easy to fetch user_id from logged in user while it was challenging to get “event_id”. Therefore to solve this purpose I worked on a module named “permission_manager.py” situated at “app/api/helpers/permission_manager.py” in the codebase

Basic Idea of Permission Manager

Permission manager basically works to serve the required attributes/view_kwargs to permission decorators so that these decorators do not break

Its logic can be described as:

    1. It first sits in the middle of a request and permission decorator
    2. Evaluates the arguments passed to it and ensure the current method of the request (POST, GET, etc ) is the part of permission check or not.
    3. Uses two important things, fetch and fetch_as
      fetch => value of this argument is the URL parameter key which will be fetched from URL or the database ( if not present in URL )
      fetch_as => the value received from fetch will be sent to permission decorator by the name as the value of this option.
    4. If the fetch key is not there in URL, It uses third parameter model which is Model if the table from where this key can be fetched and then passes it to permission decorator
    5. Returns the requested view on passing access level and Forbidden error if fails

This way it ensures that if looks for the only specific type of requests allowing us to set different rules for different methods.

if 'methods' in kwargs:
        methods = kwargs['methods']

    if request.method not in methods:
        return view(*view_args, **view_kwargs)

Implementing Permission Manager

Implementing it was a simple thing,

  1. Firstly, registration of JSON API app is shifted from app/api/__init__.py to app/api/bootstrap.py so that this module can be imported anywhere
  2. Added permission manager to the app_v1 module
  3. Created permission_manager.py in app/api/helpers
  4. Added it’s usage in different APIs

An example Usage:

decorators = (api.has_permission('is_coorganizer', fetch='event_id', fetch_as="event_id", methods="POST",
                                     check=lambda a: a.get('event_id') or a.get('event_identifier')),)

Here we are checking if the request has the permission of a Co-Organizer and for this, we need to fetch event_id  from request URI. Since no model is provided here so it is required for event_id in URL this also ensures no other endpoints can leak the resource. Also here we are checking for only POST requests thus it will pass the GET requests as it is no checking.

What’s next in permission manager?

Permission has various scopes for improving, I’m still working on a module as part of permission manager which can be used directly in the middle of views and resources so that we can check for permission for specific requests in the middle of any process.

The ability to add logic so that we can leave the check on the basis of some logic may be adding some lambda attributes will work.

Resources

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Acceptance Testing of a Feature in Open Event Frontend

In Open Event Frontend, we have integration tests for ember components which are used throughout the project. But even after those tests, user interaction could pose some errors. We perform acceptance tests to alleviate such scenarios.

Acceptance tests interact with application as the user does and ensures proper functionality of a feature or to determine whether or not the software system has met the requirement specifications. They are quite helpful for ensuring that our core features work properly.

Let us write an acceptance test for register feature in Open Event Frontend.

import { test } from 'qunit';
import moduleForAcceptance from 'open-event-frontend/tests/helpers/module-for-acceptance';

moduleForAcceptance('Acceptance | register');

In the first line we import test from ‘ember-qunit’ (default unit testing helper suite for Ember) which contains all the required test functions. For example, here we are using test function to check the rendering of our component. We can use test function multiple times to check multiple components.

Next, we import moduleForAcceptance from ‘open-event-frontend/tests/helpers/module-for-acceptance’ which deals with application setup and teardown.

test('visiting /register', function(assert) {
  visit('/register');

  andThen(function() {
    assert.equal(currentURL(), '/register');
  });
});

Inside our test function, we simulate visiting  /register route and then check for the current route to be /register.

test('visiting /register and registering with existing user', function(assert) {
  visit('/register');
  andThen(function() {
    assert.equal(currentURL(), '/register');
    fillIn('input[name=email]', '[email protected]');
    fillIn('input[name=password]', 'opev_test_user');
    fillIn('input[name=password_repeat]', 'opev_test_user');
    click('button[type=submit]');
    andThen(function() {
      assert.equal(currentURL(), '/register');
      // const errorMessageDiv = findWithAssert('.ui.negative.message');
      // assert.equal(errorMessageDiv[0].textContent.trim(), 'An unexpected error occurred.');
    });
  });
});

Then we simulate visiting /register route and register a dummy user. For this, we first go to /register route and then check for the current route to be register route. We fill the register form with appropriate data and hit submit.

test('visiting /register after login', function(assert) {
  login(assert);
  andThen(function() {
    visit('/register');
    andThen(function() {
      assert.equal(currentURL(), '/');
    });
  });
});

The third test is to simulate visiting /register route with user logged in and this is very simple. We just visit /register route and then check if we are are at / route or not because a user redirects to / route when he tries to visit /register after login.

And since we checked for all the possible combinations, to run the test we simply use the following command-

ember test --server

But there is a little demerit to acceptance tests. They boot up the whole EmberJS application and start us at the application.index route. We then have to navigate to the page that contains the feature being tested. Writing acceptance tests for each and every feature would be a big waste of time and CPU cycles. For this reason, only core features are tested for acceptance.

Resources

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Implement Caching in the Live Feed of Open Event Android App

In the Open Event Android App, a live feed from the event’s Facebook page was recently implemented. Since it was a live feed, it was decided that it was futile to store it in the Realm database of the app. The data of the live feed didn’t persist anywhere, hence the feed used to be empty when the app ran without the internet connection.

To solve the problem of data persistence, it was decided to store the feed in the cache. Now, there were two paths before us – use retrofit okhttp cache management or use volley. Since retrofit is used to make the API requests in the app, we used the former. To implement caching with retrofit, its API response should include the cache control header. Since it was not a response generated by a personal server, interceptors were needed to force change the request.

Interceptors

Interceptors are a powerful mechanism that can monitor, rewrite, and retry calls. The solution was to use interceptors to rewrite the calls to force use of cache. Two interceptors were added, application interceptor for the request and the network interceptor for the response.

Implementation

Create a cache file to store the response.

private static Cache provideCache() {
   Cache cache = null;
   try {
       cache = new Cache(new File(OpenEventApp.getAppContext().getCacheDir(), "facebook-feed-cache"),
               10 * 1024 * 1024); // 10 MB
   } catch (Exception e) {
       Timber.e(e, "Could not create Cache!");
   }
   return cache;
}

 

Create a network interceptor by chaining the response with the cache control header and removing the pragma header to force use of cache.

private static Interceptor provideCacheInterceptor() {
   return chain -> {
       Response response = chain.proceed(chain.request());

       // re-write response header to force use of cache
       CacheControl cacheControl = new CacheControl.Builder()
               .maxAge(2, TimeUnit.MINUTES)
               .build();

       return response.newBuilder()
               .removeHeader("Pragma")
               .header(CACHE_CONTROL, cacheControl.toString())
               .build();
   };
}

 

Create an application interceptor by chaining the request with the cache control header for stale responses and removing the pragma header to make the feed available for offline usage.

private static Interceptor provideOfflineCacheInterceptor() {
   return chain -> {
       Request request = chain.request();

       if (!NetworkUtils.haveNetworkConnection(OpenEventApp.getAppContext())) {
           CacheControl cacheControl = new CacheControl.Builder()
                   .maxStale(7, TimeUnit.DAYS)
                   .build();

           request = request.newBuilder()
                   .removeHeader("Pragma")
                   .cacheControl(cacheControl)
                   .build();
       }

       return chain.proceed(request);
   };
}

 

Finally add the cache and the two interceptors while building the okhttp client.

OkHttpClient okHttpClient = okHttpClientBuilder.addInterceptor(new HttpLoggingInterceptor()
       .setLevel(HttpLoggingInterceptor.Level.BASIC))
       .addInterceptor(provideOfflineCacheInterceptor())
       .addNetworkInterceptor(provideCacheInterceptor())
       .cache(provideCache())
       .build();

 

Conclusion

Working of apps without the internet connection builds up a strong case for corner cases while testing. It is therefore critical to persist data however small to avoid crashes and bad user experience.

Resources

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Adding Masonry Grid Layout to loklak Media Wall

Working on loklak media walls, I wanted to add a responsive self-adjusting grid layout for media walls. Going through the most trending media wall, I concluded that the most commonly used view for media walls is Masonry view. This view is a much similar view to the Pinterest grid layout. In fact, Masonry Desandro states that Masonry view can be one of the most responsive and most pretty ways to present cards. It is also beneficial to use masonry view as it avoids unnecessary gaps and makes full use of the display screen.

In this blog, we are going to see how I added a masonry view to the media walls without any other dependency than CSS using column-count and column-gap. We would also be looking upon how to adjust font-size using rem units to make text readable for all screen-sizes depending on number of columns.

HTML File

<span class=“masonry”>
<span class=“masonry-panel” *ngFor=“let item of (apiResponseResults$ | async)”>
<span class=“masonry-content”>
<mediawallcard [feedItem]=“item”></mediawallcard>
</span>
</span>
</span>
  • The first span with class masonry is like a container in which all the cards will be embedded. This div will provide a container to adjust the number of columns in which cards will be adjusted.
  • The second span with class masonry-panel will be the column division. These panels are like the elements of a matrix. These panels are responsive and will adjust according to the screen size.
  • The third span with class masonry-content are like the content box in which all the content will be embedded. This div will create a space in the panel for the card to be adjusted.
  • The fourth element media-wall-card are the cards in which all the feed items are placed.

CSS File

  • Adjusting columns – The column-count and column-gap property was introduced in CSS3 to divide the element in a specified number of column and to keep the specified number (whole number) of column gap between the elements respectively. For different screen sizes, these are the column count that are kept. We need adjust the number of columns according to various screen sizes so that cards neither look too stretched or too bleak. Media wall is now responsive enough to adjust on smaller screens like mobiles with one column and on larger screens too with five columns.

@media only screen and (max-width: 600px) {
.masonry {
columncount: 1;
columngap: 0;
}
} @media only screen and (min-width: 600px) and (max-width: 900px) {
.masonry {
columncount: 2;
columngap: 0;
}
} @media only screen and (min-width: 1280px) and (max-width: 1500px) {
.masonry {
columncount: 3;
columngap: 0;
}
} @media only screen and (min-width: 1500px) and (max-width: 1920px) {
.masonry {
columncount: 4;
columngap: 0;
}
} @media only screen and (min-width: 1920px) {
.masonry {
columncount: 5;
columngap: 0;
}
}
  • Adjusting Font-Size – For a fixed aspect ratio of various divisions of the media wall card, we need a central unit that can be adjusted to keep this ratio fixed. Using px will rather make the sizes fixed and adjusting these sizes for various screen sizes will make it hectic and would spoil the ratio. We will be instead using rem as a font-unit to adjust the font size for different screen sizes. Firstly, we need to assign a certain font size to all the elements in the media wall card. Now, we can configure the central font-size of the root unit for all the screen sizes using @media tag.

One thing that should be kept in mind is that The root font size should be kept more than 14px always.

@media only screen and (max-width: 600px) {
:root {
font-size: 14px;
}
}@media only screen and (min-width: 600px) and (max-width: 800px) {
:root {
font-size: 16px;
}
}@media only screen and (min-width: 800px) and (max-width: 1200px) {
:root {
font-size: 17px;
}
}@media only screen and (min-width: 1200px) and (max-width: 1500px) {
:root {
font-size: 18px;
}
}@media only screen and (min-width: 1500px) {
:root {
font-size: 20px;
}
}

 

This will create a masonry layout and now, all the cards can be adjusted in this self-adjusting grid and will look readable on all types of screen.

Reference

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Addition of Bookmarks to the Homescreen in the Open Event Android App

In the Open Event Android app we had already built the new homescreen but the users only had access to bookmarks in a separate page which could be accessed from the navbar.If the bookmarks section were to be incorporated in the homescreen itself, it would definitely improve its access to the user. In this blog post, I’ll be talking about how this was done in the app.

These 2 images show the homescreen and the bookmarks section respectively.

No Bookmark View
Bookmark View

 

 

 

 

 

 

 

 

 

This was the proposed homescreen page for the app. This would provide easy access to important stuff to the user such as event venue,date,description etc. Also the same homescreen would also have the bookmarks showing at the top if there are any.

The list of bookmarks in the first iteration of design was modeled to be a horizontal list of cards.

Bookmarks Merging Process

These are some variables for reference.

private SessionsListAdapter sessionsListAdapter;
 private RealmResults<Session> bookmarksResult;
 private List<Session> mSessions = new ArrayList<>();

The code snippet below highlights the initial setup of the bookmarks recycler view for the horizontal List of cards. All of this is being done in the onCreateView callback of the AboutFragment.java file which is the fragment file for the homescreen.

bookmarksRecyclerView.setVisibility(View.VISIBLE);
 sessionsListAdapter = new SessionsListAdapter(getContext(), mSessions, bookmarkedSessionList);
 sessionsListAdapter.setBookmarkView(true);
 bookmarksRecyclerView.setAdapter(sessionsListAdapter);
 bookmarksRecyclerView.setLayoutManager(new LinearLayoutManager(getContext(),LinearLayoutManager.HORIZONTAL,false));

The SessionListAdapter is an adapter that was built to handle multiple types of displays of the same viewholder i.e SessionViewHolder . This SessionListAdapter is given a static variable as an argument which is just notifies the adapter to switch to the bookmarks mode for the adapter.

private void loadData() {
    bookmarksResult = realmRepo.getBookMarkedSessions();
    bookmarksResult.removeAllChangeListeners();
    bookmarksResult.addChangeListener((bookmarked, orderedCollectionChangeSet) -> {
        mSessions.clear();
        mSessions.addAll(bookmarked);
 
        sessionsListAdapter.notifyDataSetChanged();
 
        handleVisibility();
    });
 }

This function loadData() is responsible for extracting the sessions that are bookmarked from the local Realm database. We the update the BookmarkAdapter on the homescreen with the list of the bookmarks obtained. Here we see that a ChangeListener is being attached to our RealmResults. This is being done so that we do our adapter notify only after the data of the bookmarked sessions has been processed from a background thread.

if(bookmarksResult != null)
    bookmarksResult.removeAllChangeListeners();

And it is good practice to remove any ChangeListeners that we attach during the fragment life cycle in the onStop() method to avoid memory leaks.

So now we have successfully added bookmarks to the homescreen.

Resources

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Better Bookmark Display Viewholder in Home Screen of the Open Event Android App

Earlier in the Open Event Android app we had built the homescreen with the bookmarks showing up at the top as a horizontal list of cards but it wasn’t very user-friendly in terms of UI. Imagine that a user bookmarks over 20-30 sessions, in order to access them he/she might have to scroll horizontally a lot in order to access his/her bookmarked session. So this kind of UI was deemed counter-intuitive. A new UI was proposed involving the viewholder used in the schedule page i.e DayScheduleViewHolder, where the list would be vertical instead of horizontal. An added bonus was that this viewholder conveyed the same amount of information on lesser white space than the earlier viewholder i.e SessionViewHolder.

Old Design
New Design

 

 

 

 

 

 

 

 

 

Above are two images, one in the initial design, the second in the new design. In the earlier design the number of bookmarks visible to the user at a time was at most 1 or 2 but now with the UI upgrade a user can easily see up-to 5-6 bookmarks at a time. Additionally there is more relevant content visible to the user at the same time.

Additionally this form of design also adheres to Google’s Material Design guidelines.

Code Comparison of the two Iterations

Initial Design
sessionsListAdapter = new SessionsListAdapter(getContext(), mSessions, bookmarkedSessionList);
 sessionsListAdapter.setBookmarkView(true);
 bookmarksRecyclerView.setAdapter(sessionsListAdapter);
 bookmarksRecyclerView.setLayoutManager(new LinearLayoutManager(getContext(),LinearLayoutManager.HORIZONTAL,false));

Here we are using the SessionListAdapter for the bookmarks. This was previously being used to display the list of sessions inside the track and location pages. It is again being used here to display the horizontal list of bookmarks.To do this we are using the function setBookmarkView(). Here mSessions consists the list of bookmarks that would appear in the homescreen.

Current Design
bookmarksRecyclerView.setVisibility(View.VISIBLE);
 bookMarksListAdapter = new DayScheduleAdapter(mSessions,getContext());
 bookmarksRecyclerView.setAdapter(bookMarksListAdapter);
 bookmarksRecyclerView.setLayoutManager(new LinearLayoutManager(getContext()));

Now we are using the DayScheduleAdapter which is the same adapter used in the schedule page of the app. Now we use a vertical layout instead of a horizontal layout  but with a new viewholder design. I will be talking about the last line in the code snippet shortly.

ViewHolder Design (Current Design)

<RelativeLayout android:id="@+id/content_frame">
    <LinearLayout android:id="@+id/ll_sessionDetails">
        <TextView android:id="@+id/slot_title"/>
        <RelativeLayout>
            <TextView android:id="@+id/slot_start_time”/>
            <TextView android:id="@+id/slot_underscore"/>
            <TextView android:id="@+id/slot_end_time"/>

           <TextView android:id="@+id/slot_comma"/>
            <TextView android:id="@+id/slot_location”/>
            <Button android:id="@+id/slot_track"/>
            <ImageButton android:id="@+id/slot_bookmark"/>
        </RelativeLayout>

    </LinearLayout>
    <View android:id=”@+id/divider”/>
 </RelativeLayout>

This layout file is descriptive enough to highlight each element’s location.

In this viewholder we can also access to the track page from the track tag and can also remove bookmarks instantly.

The official widget to make a scroll layout in android is ScrollView. Basically, adding a RecyclerView inside ScrollView can be difficult . The problem was that the scrolling became laggy and weird.  Fortunately, with the appearance of Material Design , NestedScrollView was released and this becomes much easier.

bookmarksRecyclerView.setNestedScrollingEnabled(false);

With this small snippet of code we are able to insert a RecyclerView inside the NestedScrollView without any scroll lag.
So now we have successfully updated the UI/UX for the homescreen  to meet the requirements as given by the Material Design guidelines.

Resources

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Maintain Aspect Ratio Mixin on Open Event Frontend

The welcome page of the Open-Event-Frontend is designed to contain cards that represent an event. A user is directed to the event-details page by clicking on the corresponding card. The page consists of an image that serves as the banner for the event and an overlapping div to provide some contrast against the image. A comment may also be added onto the image and along with the overlapping div it is wrapped in a container div.

Since we have given a specific height to the contrasting div, the background image shrinks according to the screen size but the contrasting div does not whenever we go from a large screen to a smaller screen.

Mobile view (before):-

We want our contrasting div also to resize in accordance to the image. To do it, we first define a sass mixin to maintain a common aspect ratio for image and overlapping div. Let us see it’s code.

 @mixin aspect-ratio($width, $height) {
    position: relative;
    &:before {
      display: block;
      content: "";
      width: 100%;
      padding-top: ($height / $width) * 100%;
    }
    > .content {
      position: absolute;
      top: 0;
      left: 0;
      right: 0;
      bottom: 0;
    }
    > img {
      position: absolute;
      top: 0;
      left: 0;
      right: 0;
      bottom: 0;
    }
  }

So what does this mixin actually doing is we are passing the height and width of the image and we are defining a pseudo element for our image and give it a margin top of (height/width)*100 since this value is related to image width (height: 0; padding-bottom: 100%; would also work, but then we have to adjust the padding-bottom value every time we change the width). Now we just position the content element and image as absolute with all four orientations set to 0. This just covers the parent element completely, no matter which size it has.

Now we can simply use our mixin by adding the following line of code in out container div

@include aspect-ratio(2, 1);

Here we want to maintain a 2:1 aspect ratio and the user is also expected to upload the image in the same aspect ratio. Therefore, we pass width as 2 and height as 1 to our mixin.

Now when we resize our screen both the image and the overlapping div resize maintaining 2:1 aspect ratio.

Mobile view (after):-

Resources

  • mademyday blog describes a method of using pseudo elements to maintain an element’s aspect ratio.
  • css-tricks snippet.
Continue Reading Maintain Aspect Ratio Mixin on Open Event Frontend

Image Cropper On Ember JS Open Event Frontend

In Open Event Front-end, we have a profile page for every user who is signed in where they can edit their personal details and profile picture. To provide better control over profile editing to the user, we need an image cropper which allows the user to crop the image before uploading it as their profile picture. For this purpose, we are using a plugin called Croppie. Let us see how we configure Croppie in the Ember JS front-end to serve our purpose.

All the configuration related to Croppie lies in a model called cropp-model.js.

 onVisible() {
    this.$('.content').css('height', '300px');
    this.$('img').croppie({
      customClass : 'croppie',
      viewport    : {
        width  : 400,
        height : 200,
        type   : 'square'
      },
      boundary: {
        width  : 600,
        height : 300
      }
    });
  },

  onHide() {
    this.$('img').croppie('destroy');
    const $img = this.$('img');
    if ($img.parent().is('div.croppie')) {
      $img.unwrap();
    }
  },

  actions: {
    resetImage() {
      this.onHide();
      this.onVisible();
    },
    cropImage() {
      this.$('img').croppie('result', 'base64', 'original', 'jpeg').then(result => {
        if (this.get('onImageCrop')) {
          this.onImageCrop(result);
        }
      });
    }

There are two functions: onVisible() and onHide(), which are called every time when we hit reset button in our image cropper model.

  • When a user pushes reset button, the onHide() function fires first which basically destroys a croppie instance and removes it from the DOM.
  • onVisible(), which fires next, sets the height of the content div. This content div contains our viewport and zoom control. We also add a customClass of croppie to the container in case we are required to add some custom styling. Next, we set the dimensions and the type of viewport which should be equal to the dimensions of the cropped image. We define type of cropper as ‘square’ (available choices are ‘square’ and ‘circle’). We set the dimensions of our boundary. The interesting thing to notice here is that we are setting only the height of the boundary because if we pass only the height of the boundary, the width will be will be calculated using the viewport aspect ratio. So it will fit in all the screen sizes without overflowing.

The above two functions are invoked when we hit the reset button. When the user is satisfied with the image and hits ‘looks good’ button, cropImage() function is called where we are get the resulting image by passing some custom options provided by croppie like base64 bit encoding and size of cropped image which we are set to ‘original’ here and the extension of image which is we set here as ‘.jpeg’. This function returns the image of desired format which we use to set profile image.

Resources

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Addition of Bookmark Icon in Schedule ViewHolder in Open Event Android App

In the Open Event Android app we only had a list of sessions in the schedule page without  the ability to bookmark the session unless we went into the SessionDetailPage or visited the session list via the tracks page or the locations page. This was obviously very inconvenient. There were several iterations of UI design for the same. Taking cues from the Google I/O 17 App I thought that the addition of the Bookmark Icon in the Schedule ViewHolder would be helpful to the user. In this blog post I will be talking about how this feature was implemented.

Layout Implementation for the Bookmark Icon

<ImageButton
    android:id="@+id/slot_bookmark"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="end"
    android:layout_alignParentEnd="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentBottom="true"
    android:tint="@color/black"
    android:background="?attr/selectableItemBackgroundBorderless"
    android:contentDescription="@string/session_bookmark_status"
    android:padding="@dimen/padding_small"
    app:srcCompat="@drawable/ic_bookmark_border_white_24dp" />

The bookmark Icon was modelled as an ImageButton inside the item_schedule.xml file which serves as the layout file for the DayScheduleViewHolder.

Bookmark Icon Functionality in DayScheduleAdapter

The Bookmark Icon had mainly 3 roles :

  1. Add the session to the list of bookmarks (obviously)
  2. Generate the notification giving out the bookmarked session details.
  3. Generate a Snackbar if the icon was un-clicked which allowed the user to restore the bookmarked status of the session.
  4. Update the bookmarks widget.

Now we will be seeing how was all this done. Some of this was already done previously in the SessionListAdapter. We just had to modify some of the code to get our desired result.

       Session not bookmarked                      Session bookmarked                      

First we just set a different icon to highlight the Bookmarked and the un-bookmarked status. This code snippet highlights how this is done.

if(session.isBookmarked()) {
    slot_bookmark.setImageResource(R.drawable.ic_bookmark_white_24dp);
 } else {
 slot_bookmark.setImageResource(R.drawable.ic_bookmark_border_white_24dp);
 }
 slot_bookmark.setColorFilter(storedColor,PorterDuff.Mode.SRC_ATOP);

We check if the session is bookmarked by calling a function isBookmarked() and choose one of the 2 bookmark icons depending upon the bookmark status.

If a session was found out to be bookmarked and the Bookmark Icon was we use the WidgetUpdater.updateWidget() function to remove that particular session from the  Bookmark Widget of the app. During this a  Snackbar is also generated “Bookmark Removed” with an UNDO option which is functional.

realmRepo.setBookmark(sessionId, false).subscribe();
 slot_bookmark.setImageResource(R.drawable.ic_bookmark_border_white_24dp);
 
 if ("MainActivity".equals(context.getClass().getSimpleName())) {
    Snackbar.make(slot_content, R.string.removed_bookmark, Snackbar.LENGTH_LONG)
            .setAction(R.string.undo, view -> {
 
                realmRepo.setBookmark(sessionId, true).subscribe();
                slot_bookmark.setImageResource(R.drawable.ic_bookmark_white_24dp);
 
                WidgetUpdater.updateWidget(context);
            }).show();

else {
    Snackbar.make(slot_content, R.string.removed_bookmark, Snackbar.LENGTH_SHORT).show();
 }

If a session wasn’t bookmarked earlier but the Bookmark Icon was clicked we would firstly need to update the bookmark status within our local Realm Database.

realmRepo.setBookmark(sessionId, true).subscribe();

We would also create a notification to notify the user.

NotificationUtil.createNotification(session, context).subscribe(
        () -> Snackbar.make(slot_content,
                R.string.added_bookmark,
                Snackbar.LENGTH_SHORT)
                .show(),
        throwable -> Snackbar.make(slot_content,
                R.string.error_create_notification,
                Snackbar.LENGTH_LONG).show());

The static class Notification Util is responsible for the generation of notifications. The internal working of that class is not necessary right now. What this snippet of code does is that It creates a Snackbar upon successful notification with the text “Bookmark Added” and if any error occurs a Snackbar with the text “Error Creating Notification” is generated.

slot_bookmark.setImageResource(R.drawable.ic_bookmark_white_24dp);
 slot_bookmark.setColorFilter(storedColor,PorterDuff.Mode.SRC_ATOP);

This snippet of code is responsible for the colors that are assigned to the Bookmark Icons for different tracks and this color is obtained in the following manner.

int storedColor = currentSession.getTrack().getColor()

So now we have successfully added the Bookmark Icon to the ScheduleViewHolder inside the schedule of the app.

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Addition Of Track Tags In Open Event Android App

In the Open Event Android app we only had a list of sessions in the schedule page without  knowing which track each session belonged to. There were several iterations of UI design for the same. Taking cues from the Google I/O 17 App we thought that the addition of track tags would be informative to the user.  In this blog post I will be talking about how this feature was implemented.

TrackTag Layout in Session

<Button
                android:layout_width="wrap_content"
                android:layout_height="@dimen/track_tag_height"
                android:id="@+id/slot_track"
                android:textAllCaps="false"
                android:gravity="center"
                android:layout_marginTop="@dimen/padding_small"
                android:paddingLeft="@dimen/padding_small"
                android:paddingRight="@dimen/padding_small"
                android:textStyle="bold"
                android:layout_below="@+id/slot_location"
                android:ellipsize="marquee"
                android:maxLines="1"
                android:background="@drawable/button_ripple"
                android:textColor="@color/white"
                android:textSize="@dimen/text_size_small"
                tools:text="Track" />

The important part here is the track tag was modelled as a <Button/> to give users a touch feedback via a ripple effect.

Tag Implementation in DayScheduleAdapter

All the dynamic colors for the track tags was handled separately in the DayScheduleAdapter.

final Track sessionTrack = currentSession.getTrack();
       int storedColor = Color.parseColor(sessionTrack.getColor());
       holder.slotTrack.getBackground().setColorFilter(storedColor, PorterDuff.Mode.SRC_ATOP);

       holder.slotTrack.setText(sessionTrack.getName());
       holder.slotTrack.setOnClickListener(v -> {
            Intent intent = new Intent(context, TrackSessionsActivity.class);
            intent.putExtra(ConstantStrings.TRACK, sessionTrack.getName());

            intent.putExtra(ConstantStrings.TRACK_ID, sessionTrack.getId());
            context.startActivity(intent);
      });

As the colors associated with a track were all stored inside the track model we needed to obtain the track from the currentSession. We could get the storedColor by calling getColor() on the track object associated with the session.

In order to set this color as the background of the button we needed to set a color filter with a PorterDuff Mode called as SRC_ATOP.

The name of the parent class is an homage to the work of Thomas Porter and Tom Duff, presented in their seminal 1984 paper titled “Compositing Digital Images”. In this paper, the authors describe 12 compositing operators that govern how to compute the color resulting of the composition of a source (the graphics object to render) with a destination (the content of the render target).

Ref : https://developer.android.com/reference/android/graphics/PorterDuff.Mode.html

To exactly understand what does the mode SRC_ATOP do we can refer to the image below for understanding. There are several other modes with similar functionality.

               

      SRC IMAGE             DEST IMAGE           SRC ATOP DEST

Now we also set an onClickListener for the track tag so that it directs us to the tracks Page.

So now we have successfully added track tags to the app.

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