Question

I usually code

    Button button1 = (Button)findViewById(R.id.start1);
    button1.setOnClickListener(mStart1Listener);
    Button button2 = (Button)findViewById(R.id.start2);
    button2.setOnClickListener(mStart2Listener);

But in android sample, I found these in ServiceStartArgumentsController.java

    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.service_start_arguments_controller);

    // Watch for button clicks.
    Button button = (Button)findViewById(R.id.start1);
    button.setOnClickListener(mStart1Listener);
    button = (Button)findViewById(R.id.start2);
    button.setOnClickListener(mStart2Listener);
    button = (Button)findViewById(R.id.start3);
    button.setOnClickListener(mStart3Listener);
    button = (Button)findViewById(R.id.startfail);
    button.setOnClickListener(mStartFailListener);
    button = (Button)findViewById(R.id.kill);
    button.setOnClickListener(mKillListener);
}

What’s the difference between them, and why one button can add multiple ClickListener

Answer 1

What’s the difference between them, and why one button can add multiple ClickListener

A View can only have one OnClickListener. The second approach is just re-using the variable button, notice the third line:

Button button = (Button)findViewById(R.id.start1);
button.setOnClickListener(mStart1Listener);
button = (Button)findViewById(R.id.start2); // This one

It overrides the previous value of button with a new Button and the new Button will be assigned the next OnClickListener.