Android - setOnClickListener vs OnClickListener vs View OnClickListener

Question

My understanding is that when I m creating a button object that listens for a click  I have to    Create the button object Use OnClickListner to make it listen to the user s click Use onClick to execute actions after the user clicks the button   Now     Where does setOnClickListener fit into the above logic   Which one actually listens to the button click   setOnClickListener   OnClickListener   View OnClickListener   What are the differences between those three    Here is what I found in Android Dev     The example below shows how to register an on-click listener for a Button      Create an anonymous implementation of OnClickListener private OnClickListener mCorkyListener   new OnClickListener         public void onClick View v             do something when the button is clicked           protected void onCreate Bundle savedValues                   Capture our button from layout     Button button    Button findViewById R id corky          Register the onClick listener with the implementation above     button setOnClickListener mCorkyListener               You may also find it more convenient to implement OnClickListener as a part of your Activity  This will avoid the extra class load and object allocations  For example   public class ExampleActivity extends Activity implements OnClickListener       protected void onCreate Bundle savedValues                         Button button    Button findViewById R id corky            button setOnClickListener this                 Implement the OnClickListener callback     public void onClick View v             do something when the button is clicked

User · Answer

View is the superclass for all widgets and the OnClickListener interface belongs to this class. All widgets inherit this. View.OnClickListener is the same as OnClickListener. You would have to override the onClick(View view) method from this listener to achieve the action that you want for your button.

To tell Android to listen to click events for a widget, you need to do:

widget.setOnClickListener(this); // If the containing class implements the interface
// Or you can do the following to set it for each widget individually
widget.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        // Do something here
    }
});

The 'View' parameter passed in the onClick() method simply lets Android know that a view has been clicked. It can be a Button or a TextView or something else. It is up to you to set an OnClickListener for every widget or to simply make the class containing all these widgets implement the interface. In this case you will have a common onClick() method for all the widgets and all you have to do is to check the id of the view that is passed into the method and then match that against the id for each element that you want and take action for that element.

User · Answer

Imagine that we have 3 buttons for example  public class MainActivity extends ActionBarActivity         Override     protected void onCreate Bundle savedInstanceState            super onCreate savedInstanceState            setContentView R layout activity main                Capture our button from layout         Button button    Button findViewById R id corky           Button button2    Button findViewById R id corky2           Button button3    Button findViewById R id corky3              Register the onClick listener with the implementation above         button setOnClickListener mCorkyListener           button2 setOnClickListener mCorkyListener           button3 setOnClickListener mCorkyListener                  Create an anonymous implementation of OnClickListener     private View OnClickListener mCorkyListener   new View OnClickListener             public void onClick View v                   do something when the button is clicked                 Yes we will handle click here but which button clicked    We don t know                        So what we will do   public class MainActivity extends ActionBarActivity         Override     protected void onCreate Bundle savedInstanceState            super onCreate savedInstanceState            setContentView R layout activity main                Capture our button from layout         Button button    Button findViewById R id corky           Button button2    Button findViewById R id corky2           Button button3    Button findViewById R id corky3              Register the onClick listener with the implementation above         button setOnClickListener mCorkyListener           button2 setOnClickListener mCorkyListener           button3 setOnClickListener mCorkyListener                  Create an anonymous implementation of OnClickListener     private View OnClickListener mCorkyListener   new View OnClickListener             public void onClick View v                   do something when the button is clicked                Yes we will handle click here but which button clicked    We don t know                 So we will make             switch  v getId     to get clicked view id                       case R id corky                          do something when the corky is clicked                      break                  case R id corky2                          do something when the corky2 is clicked                      break                  case R id corky3                          do something when the corky3 is clicked                      break                  default                      break                                      Or we can do this   public class MainActivity extends ActionBarActivity         Override     protected void onCreate Bundle savedInstanceState            super onCreate savedInstanceState            setContentView R layout activity main                Capture our button from layout         Button button    Button findViewById R id corky           Button button2    Button findViewById R id corky2           Button button3    Button findViewById R id corky3              Register the onClick listener with the implementation above         button setOnClickListener new View OnClickListener                  Override             public void onClick View v                       do something when the corky is clicked                                   button2 setOnClickListener new View OnClickListener                  Override             public void onClick View v                       do something when the corky2 is clicked                                   button3 setOnClickListener new View OnClickListener                  Override             public void onClick View v                       do something when the corky3 is clicked                                       Or we can implement View OnClickListener and i think it s the best way   public class MainActivity extends ActionBarActivity implements View OnClickListener         Override     protected void onCreate Bundle savedInstanceState            super onCreate savedInstanceState            setContentView R layout activity main                Capture our button from layout         Button button    Button findViewById R id corky           Button button2    Button findViewById R id corky2           Button button3    Button findViewById R id corky3              Register the onClick listener with the implementation above         button setOnClickListener this           button2 setOnClickListener this           button3 setOnClickListener this                Override     public void onClick View v               do something when the button is clicked            Yes we will handle click here but which button clicked    We don t know             So we will make         switch  v getId     to get clicked view id                   case R id corky                      do something when the corky is clicked                  break              case R id corky2                      do something when the corky2 is clicked                  break              case R id corky3                      do something when the corky3 is clicked                  break              default                  break                      Finally there is no real differences here Just  Way better than the other

User · Answer

The logic is simple  setOnClickListener belongs to step 2    You create the button You create an instance of OnClickListener  like it s done in that example and override the onClick-method  You assign that OnClickListener to that button using btn setOnClickListener myOnClickListener   in your fragments activities onCreate-method  When the user clicks the button  the onClick function of the assigned OnClickListener is called     If you import android view View  you use View OnClickListener  If you import android view View    or import android view View OnClickListener  you use OnClickListener as far as I get it   Another way is to let you activity fragment inherit from OnClickListener  This way you assign your fragment activity as the listener for your button and implement onClick as a member-function

User · Answer

First of all  there is no difference between View OnClickListener and OnClickListener  If you just use View OnClickListener directly  then you don t need to write-  import android view View OnClickListener You set an OnClickListener instance  e g  myListener named object as the listener to a view via setOnclickListener    When a click event is fired  that myListener gets notified and it s onClick View view  method is called  Thats where we do our own task  Hope this helps you

User · Answer

Please note that for the sake of simplicity I have made reference to only the first code snippet i e       Create an anonymous implementation of OnClickListener private OnClickListener mCorkyListener   new OnClickListener         public void onClick View v             do something when the button is clicked           protected void onCreate Bundle savedValues                   Capture our button from layout     Button button    Button findViewById R id corky          Register the onClick listener with the implementation above     button setOnClickListener mCorkyListener               setOnClickListener View OnClickListener l  is a public method of View class  Button class extends the View class and can therefore call setOnClickListener View OnClickListener l  method   setOnClickListener registers a callback to be invoked when the view  button in your case  is clicked  This answers should answer your first two questions   1  Where does setOnClickListener fit in the above logic   Ans  It registers a callback when the button is clicked   Explained in detail in the next paragraph    2  Which one actually listens to the button click   Ans  setOnClickListener method is the one that actually listens to the button click   When I say it registers a callback to be invoked  what I mean is it will run the View OnClickListener l that is the input parameter for the method  In your case  it will be mCorkyListener mentioned in button setOnClickListener mCorkyListener   which will then execute the method onClick View v  mentioned within     Create an anonymous implementation of OnClickListener private OnClickListener mCorkyListener   new OnClickListener         public void onClick View v             do something when the button is clicked            Moving on further  OnClickListener is an Interface definition for a callback to be invoked when a view  button in your case  is clicked  Simply saying  when you click that button  the methods within mCorkyListener  because it is an implementation of OnClickListener  are executed  But  OnClickListener has just one method which is OnClick View v   Therefore  whatever action that needs to be performed on clicking the button must be coded within this method   Now that you know what setOnClickListener and OnClickListener mean  I m sure you ll be able to differentiate between the two yourself  The third term View OnClickListener is actually OnClickListener itself  The only reason you have View preceding it is because of the difference in the import statment in the beginning of the program  If you have only import android view View  as the import statement you will have to use View OnClickListener  If you mention either of these import statements  import android view View    or import android view View OnClickListener  you can skip the View  and simply use OnClickListener

[android] Android - setOnClickListener vs OnClickListener vs View.OnClickListener

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