Building the interface

To be able to place the call, you need to add three elements to the screen:

• A TextView to show the connection status
• A Button to start the call
• A Button to end the call

Open the app/res/layout/activity_main.xml file. Click the Code button in the top right corner:

Replace the file contents with the following:

You will control the view using code, so you have to store references to the views. Add these properties at the top of the MainActivity class:

private Button startCallButton;
private Button endCallButton;
private TextView connectionStatusTextView;

Now you need to assign views to previously added properties and add callbacks to the buttons. Add below code to the onCreate method inside MainActivity class (below request permissions code):

// init views
startCallButton = findViewById(R.id.startCallButton);
endCallButton = findViewById(R.id.endCallButton);
connectionStatusTextView = findViewById(R.id.connectionStatusTextView);

startCallButton.setOnClickListener(v -> startCall());
endCallButton.setOnClickListener(v -> hangup());

To make code compile add these two empty methods in the MainActivity class:

@SuppressLint("MissingPermission")
private void startCall() {
        // TODO: update body
}

private void hangup() {
        // TODO: update body
}

You will fill the body of these methods in the following steps of this tutorial.

Build and Run

Run the project again (Ctrl + R).

Notice that buttons are hidden by default:

The state of the connection will be displayed and the START CALL button will be shown after logging in the user.