Task 8: Second Fragment

Step 1: Add a TextView for the random number
- Open fragment_second.xml (app > res > layout > fragment_second.xml) and switch to Design View if needed. Notice that it has a ConstraintLayout that contains a TextView and a Button.

- Set the text to "R". This text is just a placeholder until the random number is generated.
- Set the layout_constraintVertical_bias to 0.45.
- This TextView is constrained on all edges, so it's better to use a vertical bias than margins to adjust the vertical position, to help the layout look good on different screen sizes and orientations. 10. If you get a warning "Not Horizontally Constrained," add a constraint from the start of the button to the left side of the screen and the end of the button to the right side of the screen.
- Here is the XML code for the TextView that displays the random number:

Step 2: Update the TextView to display the header
- In fragment_second.xml, select textview_second, which currently has the text "Hello second fragment. Arg: %1$s" in the hello_second_fragment string resource.
- If android:text isn't set, set it to the hello_second_fragment string resource.

Step 3: Change the background color of the layout
- Give your new activity a different background color than the first activity:
- In colors.xml, add a new color resource:

- In the layout for the second activity, fragment_second.xml, set the background of the ConstraintLayoutto the new color.
- In the Attributes panel:

- Your app now has a completed layout for the second fragment. But if you run your app and press the Random button, it may crash. The click handler that Android Studio set up for that button needs some changes. In the next task, you will explore and fix this error.
Step 4: Examine the navigation graph
- When you created your project, you chose Basic Activity as the template for the new project. When Android Studio uses the Basic Activity template for a new project, it sets up two fragments, and a navigation graph to connect the two. It also set up a button to send a string argument from the first fragment to the second. This is the button you changed into the Random button. And now you want to send a number instead of a string.
- Open nav_graph.xml (app > res > navigation > nav_graph.xml).
- A screen similar to the Layout Editor in Design view appears. It shows the two fragments with some arrows between them. You can zoom with + and - buttons in the lower right, as you did with the Layout Editor.
- You can freely move the elements in the navigation editor. For example, if the fragments appear with SecondFragment to the left, drag FirstFragment to the left of SecondFragment so they appear in the order you work with them.

Step 5: Enable SafeArgs
- This will enable SafeArgs in Android Studio.
- Open Gradle Scripts > build.gradle (Project: My First App)
- Find the dependencies section In the buildscript section, and add the following lines after the other classpath entries:

- Open Gradle Scripts > build.gradle (Module: app)
- Just below the other lines that begin with apply plugin add a line to enable SafeArgs:

Android Studio should display a message about the Gradle files being changed. Click Sync Now on the right hand side.
After a few moments, Android Studio should display a message in the Sync tab that it was successful:

- Choose Build > Make Project. This should rebuild everything so that Android Studio can find FirstFragmentDirections.
- Troubleshooting: If the sync was not successful, confirm that you added the correct lines to the correct Gradle file. If there are still problems, check the developer's guide about Safe Args for an updated nav_version or other changes.
Step 6: Create the argument for the navigation action
- In the navigation graph, click on FirstFragment, and look at the Attributes panel to the right. (If the panel isn't showing, click on the vertical Attributes label to the right.)
- In the Actions section, it shows what action will happen for navigation, namely going to SecondFragment.
- Click on SecondFragment, and look at the Attributes panel.
- The Arguments section shows Nothing to show.
- Click on the + in the Arguments section.
- In the Add Argument dialog, enter myArg for the name and set the type to Integer, then click the Add button.

Step 7: Send the count to the second fragment
- The Next/Random button was set up by Android Studio to go from the first fragment to the second, but it doesn't send any information. In this step you'll change it to send a number for the current count. You will get the current count from the text view that displays it, and pass that to the second fragment.
- Open FirstFragment.java (app > java > com.example.myfirstapp > FirstFragment)
- Find the method onViewCreated() and notice the code that sets up the click listener to go from the first fragment to the second.
- Replace the code in that click listener with a line to find the count text view, textview_first.

- Run your app. Click the Count button a few times. Now when you press the Random button, the second screen shows the correct string in the header, but still no count or random number, because you need to write some code to do that.
Step 8: Update SecondFragment to compute and display a random number
- You have written the code to send the current count to the second fragment. The next step is to add code to SecondFragment.java to retrieve and use the current count.
- In SecondFragment.java, add an import for navArgs to the list of imported libraries.

- Run the app. Press the Count button a few times, then press the Random button. Does the app display a random number in the new activity?