Android OnClickListener - identify a button

Question

I have the activity:

public class Mtest extends Activity {
  Button b1;
  Button b2;
  public void onCreate(Bundle savedInstanceState) {
    ...
    b1 = (Button) findViewById(R.id.b1);
    b2 = (Button) findViewById(R.id.b2);
    b1.setOnClickListener(myhandler);
    b2.setOnClickListener(myhandler);
    ...
  }
  View.OnClickListener myhandler = new View.OnClickListener() {
    public void onClick(View v) {
      // MY QUESTION STARTS HERE!!!
      // IF b1 do this
      // IF b2 do this
      // MY QUESTION ENDS HERE!!!
    }
  }
}

How do I check which button has been clicked?

Solution 1

You will learn the way to do it, in an easy way, is:

public class Mtest extends Activity {
  Button b1;
  Button b2;
  public void onCreate(Bundle savedInstanceState) {
    ...
    b1 = (Button) findViewById(R.id.b1);
    b2 = (Button) findViewById(R.id.b2);
    b1.setOnClickListener(myhandler1);
    b2.setOnClickListener(myhandler2);
    ...
  }
  View.OnClickListener myhandler1 = new View.OnClickListener() {
    public void onClick(View v) {
      // it was the 1st button
    }
  };
  View.OnClickListener myhandler2 = new View.OnClickListener() {
    public void onClick(View v) {
      // it was the 2nd button
    }
  };
}

Or, if you are working with just one clicklistener, you can do:

View.OnClickListener myOnlyhandler = new View.OnClickListener() {
  public void onClick(View v) {
      switch(v.getId()) {
        case R.id.b1:
          // it was the first button
          break;
        case R.id.b2:
          // it was the second button
          break;
      }
  }
}

Though, I don't recommend doing it that way since you will have to add an if for each button you use. That's hard to maintain.

Solution 2

Or you can try the same but without listeners. On your button XML definition:

android:onClick="ButtonOnClick"

And in your code define the method ButtonOnClick:

public void ButtonOnClick(View v) {
    switch (v.getId()) {
      case R.id.button1:
        doSomething1();
        break;
      case R.id.button2:
        doSomething2();
        break;
      }
}

Solution 3

I prefer:

class MTest extends Activity implements OnClickListener {
    public void onCreate(Bundle savedInstanceState) {
    ...
    Button b1 = (Button) findViewById(R.id.b1);
    Button b2 = (Button) findViewById(R.id.b2);
    b1.setOnClickListener(this);
    b2.setOnClickListener(this);
    ...
}

And then:

@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.b1:
            ....
            break;
        case R.id.b2:
            ....
            break;
    }   
}

Switch-case is easier to maintain than if-else, and this implementation doesn't require making many class variables.

Solution 4

Five Ways to Wire Up an Event Listener is a great article overviewing the various ways to set up a single event listener. Let me expand that here for multiple listeners.

1. Member Class

public class main extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //attach an instance of HandleClick to the Button
        HandleClick handleClick = new HandleClick();
        findViewById(R.id.button1).setOnClickListener(handleClick);
        findViewById(R.id.button2).setOnClickListener(handleClick);
    }    
    private class HandleClick implements OnClickListener{
        public void onClick(View view) {
            switch(view.getId()) {
            case R.id.button1:
                // do stuff
                break;
            case R.id.button2:
                // do stuff
                break;
            }
        }
    }
}

2. Interface Type

public class main extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        findViewById(R.id.button1).setOnClickListener(handleClick);
        findViewById(R.id.button2).setOnClickListener(handleClick);
    }
    private OnClickListener handleClick = new OnClickListener() {
        public void onClick(View view) {
            switch (view.getId()) {
            case R.id.button1:
                // do stuff
                break;
            case R.id.button2:
                // do stuff
                break;
            }
        }
    };
}

3. Anonymous Inner Class

public class main extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        findViewById(R.id.button1).setOnClickListener(new OnClickListener() {
            public void onClick(View view) {
                // do stuff
            }
        });
        findViewById(R.id.button2).setOnClickListener(new OnClickListener() {
            public void onClick(View view) {
                // do stuff
            }
        });
    }
}

4. Implementation in Activity

public class main extends Activity implements OnClickListener {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        findViewById(R.id.button1).setOnClickListener(this);
        findViewById(R.id.button2).setOnClickListener(this);
    }
    public void onClick(View view) {
        switch (view.getId()) {
        case R.id.button1:
            // do stuff
            break;
        case R.id.button2:
            // do stuff
            break;
        }
    }
}

5. Attribute in View Layout for OnClick Events

public class main extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
    public void HandleClick(View view) {
        switch (view.getId()) {
        case R.id.button1:
            // do stuff
            break;
        case R.id.button2:
            // do stuff
            break;
        }
    }
}

And in xml:

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="HandleClick" />
<Button
    android:id="@+id/button2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="HandleClick" />

Solution 5

If you don't want to save instances of the 2 button in the class code, follow this BETTER way (this is more clear and fast!!) :

public void buttonPress(View v) {
  switch (v.getId()) {
    case R.id.button_one:
        // do something
        break;
    case R.id.button_two:
        // do something else
        break;
    case R.id.button_three:
        // i'm lazy, do nothing
        break;
  }
}

View more solutions

Comments

[Cristian]

Well, actually that's not correct. View is not a Button, but Button is a View. Though, you can cast a View to a Button. Keep in mind that the second way to do it is not recommended... maybe that v may not be a Button, which will generate a cast exception.

[Andy Zhang]

Another option would be to do a "if (v instanceof Button) { // Cast to Button and do stuff here }"

[ognian]

Actually both ways are not recommended, see my answer

[slayton]

Its actually quite simple to replace the if, elses with a single switch case statement that you switch on the id of the view and the cases are id's from R.java

[nuala]

Just wondering why you cast v to a Button anyway. getId() is defined for Views as well. Therefore I really wouldn't recommend the 2nd method but prefer Christian's solution!

[Dennis]

Much cleaner than the other answers that use a bunch of event handlers, if statements, and listeners. Listeners are great if buttons are created at runtime, but that's often not the case.

[donfede]

While an interesting different approach, XML hooks for listeners are rough around the corners with Fragments, as the callback must reside in the activity (not the fragment).

[gkiko]

This worked perfectly. You need to implement OnClickListener-android.view.View and not OnClickListener-android.content.DialogInterface

[Quasaur]

My prob is doSomething2() cant be reached without throwing either an InvocationTargetException or a NullPointerException (or both).

[user1324936]

because it is no longer possible since v14 where ids are not treated not constant

[SebasSBM]

@ognian I followed up to here because you said the main answer uses deprecated approaches. Nowadays with Android 5.0 Lollipop released, is your answer still true, or time made it become a falacy, like the comment above suggests? I really don't know what to think, or which direction to take from here.

[Hubert Grzeskowiak]

Just a sidenote: the statement "without listeners" here is wrong. You're only declaring the listener in XML, that's all.

[cessor]

I came here looking for a method to pass additional parameters to a handler, this is exactly what I wanted. The tag can be declared in Markup.

[Pang]

This is more or less just a repeat of some of the existing answers.