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Android Apprentice

Fourth Edition · Android 11 · Kotlin 1.4 · Android Studio 4.1

Before You Begin

Section 0: 5 chapters
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Section I: Your First Android App

Section 1: 5 chapters
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Section II: Building a List App

Section 2: 7 chapters
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Section III: Creating Map-Based Apps

Section 3: 7 chapters
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Section IV: Building a Podcast Manager & Player

Section 4: 8 chapters
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Section V: Android Compatibility

Section 5: 2 chapters
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Section VI: Publishing Your App

Section 6: 3 chapters
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17. Detail Activity
Written by Kevin D Moore

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In this chapter, you’ll add the ability to edit bookmarks. This involves creating a new Activity to display the bookmark details with editable fields.

Getting started

If you’re following along with your own app, copy ic_action_done.png from the starter project in the res/drawable-xxxx/ folders into your project. Make sure to copy the files from all of the drawable folders, including everything with the .hdpi, .mdpi, .xhdpi, and .xxhdpi extensions.

If you want to use the starter project instead, locate the projects folder for this chapter and open the PlaceBook app inside the starter folder. If you do use the starter app, don’t forget to add your google_maps_key in google_maps_api.xml. Read Chapter 13 for more details about the Google Maps key.

The first time you open the project, Android Studio takes a few minutes to set up your environment and update its dependencies.

Fixing the info window

Before moving on, you need to track down and fix that pesky bug left over from the previous chapter where the app crashes when tapping on a blue marker. The desired behavior is:

Saving an image

Although you can add an image directly to the Bookmark model class and let the Room library save it to the database, it’s not a best practice to store large chunks of data in the database. A better method is to store the image as a file that’s linked to the record in the database.

Adding the image to the bookmark

Next, you need to set the image for a bookmark when it’s added to the database.

Simplifying the bookmark process

Before testing this new functionality there’s a small change you can make to simplify the process of adding a new bookmark.

Using Device File Explorer

If you want to verify the image was saved and take a peek behind the scenes at how Android stores files, you can use the Device File Explorer in Android Studio. This is a handy tool for working directly with the Android file system.

Loading an image

It’s time to load the image from a file. This is considerably easier than saving an image because Android provides a method on BitmapFactory for loading images from files.

Updating BookmarkMarkerView

Now that you can load the image from where it’s stored, it’s time to update BookmarkMarkerView to provide the image for the View.

Loading images on-demand

Open MapsViewModel.kt and replace the BookmarkMarkerView data class definition with the following:

Updating the Info window

Open MapsViewModel.kt and update the BookmarkMarkerView declaration to match the following:

Bookmark detail activity

You’ve waited patiently, and it’s finally time to build out the detail Activity for editing a bookmark. For that, you’ll add a new screen that allows the user to edit key details about the bookmark, along with a custom note. You’ll do this by creating a new Activity that displays when a user taps on an Info window.

Designing the edit screen

Before creating the Activity, let’s go over the screen layout and the main elements that will be incorporated.

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Introducing Data Binding

Previously Google recommended using Kotlin Android extensions for referring to layout fields in classes. Now Google recommends using either View Binding or Data Binding. From Google:

Defining styles

First, you need to define some standard styles that are required when using the support library version of the toolbar.

Creating the details layout

Finally, you need to create the bookmark details Layout based on the design. The Activity will use all of the new styles you just added to the project.

Details activity class

Now that the bookmark details Layout is complete, you can create the details Activity to go along with it.

Updating the manifest

Next, open AndroidManifest.xml and replace the BookmarkDetailsActivity activity with:

Starting the details Activity

You can now hook up the new details Activity to the main maps Activity. You’ll detect when the user taps on a bookmark Info window, and then start the details Activity.

Populating the bookmark

The Activity has the general look you want, but it lacks any knowledge about the bookmark. To fix this, you’ll pass the bookmark ID to the Activity so that it can display the bookmark data.

Adding the data tag

Now that you have created the BookmarkDetailsView class, you can add a variable to the activity_bookmark_details.xml file. Right after the <layout> tag add:

Adding notes to the database

Before continuing, you need a way to store notes for a bookmark.

Bookmark view model

That’s all you need to support the revised Bookmark model in the database. Now you need to convert the database model to a view model.

Retrieving the bookmark view

You’re ready to add the code to retrieve the BookmarkDetailsView LiveData object in the View Activity.

Using the intent data

When the user taps on the Info window for a bookmark on the maps Activity, it passes the bookmark ID to the details Activity.

Finishing the detail activity

You’re ready to pull everything together by adding the following call to the end of onCreate() in BookmarkDetailsActivity.

Saving changes

The only major feature left is to save the user’s edits. For that, you’ll add a checkmark Toolbar item to trigger the save.

Key Points

Placebook is starting to take shape. In this chapter you learned:

Where to go from here?

Congratulations! You can now edit bookmarks, but there’s still more work to do. The next chapter wraps things up by adding some additional features and putting the finishing touches on the app.

16. Saving Bookmarks with Room
18. Navigation & Photos
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