Android 9 Development Cookbook(Third Edition)
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How it works...

As you can see, getting the results back is relatively straightforward. We just call the intent with startActivityForResult, indicating we want a result back. We set up the onActivityResult() callback handler to receive the results. Finally, we make sure that the second activity returns a result with setResult() before closing the activity. In this example, we are just setting a result with a static value. We use a simple Toast to display the result back to the user.

It's good practice to check the result code to make sure that the user didn't cancel the action. It's technically an integer, but the system uses it as a Boolean value. Check for either RESULT_OK or RESULT_CANCEL and proceed accordingly. In our example, the second activity doesn't have a cancel button, so why bother to check? What if the user hits the back button? Android will set the result code to RESULT_CANCEL and the intent to null, which would cause our code to throw an exception if we attempt to access the null result.

We made use of the Toast object, which displays a convenient pop-up message to unobtrusively notify the user. It also functions as a handy method for debugging as it doesn't need a special layout or screen space.