Android setOnClickListener method - How does it work

Question

I have trouble understanding this code  I get that findViewById will get the button widget and then it ll cast it  Then  it s going to use the button to call the setOnClickListener method  However  I don t know what is that argument being passed into the setOnClickListener and I have never seen code like that before  How is it that it creates a new object but is able to create a method of its own within another method s argument  Would be great if someone could explain that  Also  what type of object is the setOnClickListener method taking in   btn    Button findViewById R id firstButton   btn setOnClickListener new View OnClickListener          Override     public void onClick View v                tv setText months rand nextInt 12             tv setTextColor Color rgb rand nextInt 255  1  rand nextInt 255  1  rand nextInt 255  1

User · Answer

It works by same principle of anonymous inner class where we can instantiate an interface without actually defining a class   Ref  https   www geeksforgeeks org anonymous-inner-class-java

User · Answer

This is the best way to implement Onclicklistener for many buttons in a row implement View onclicklistener   public class MainActivity extends AppCompatActivity implements View OnClickListener     This is a button in the MainActivity   Override protected void onCreate Bundle savedInstanceState        super onCreate savedInstanceState       setContentView R layout activity main        bt submit    Button  findViewById R id submit        bt submit setOnClickListener this       This is an override method       Override     public void onClick View view            switch  view getId                 case R id submit                    action                  break               case R id secondbutton                    action                 break

User · Answer

It works like this  View OnClickListenere is defined -   public interface OnClickListener       void onClick View v       As far as we know you cannot instantiate an object OnClickListener  as it doesn t have a method implemented  So there are two ways you can go by - you can implement this interface which will override onClick method like this   public class MyListener implements View OnClickListener        Override     public void onClick  View v                your code here            But it s tedious to do it each time as you want to set a click listener  So in order to avoid this you can provide the implementation for the method on spot  just like in an example you gave    setOnClickListener takes View OnClickListener as its parameter

User · Answer

That what manual says about setOnClickListener method is   public void setOnClickListener  View OnClickListener l       Added in API level 1 Register a callback to be invoked when this view   is clicked  If this view is not clickable  it becomes clickable    Parameters     l View OnClickListener  The callback that will run   And normally you have to use it like this   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                   Take a look at this lesson as well Building a Simple Calculator using Android Studio

User · Answer

its an implementation of anonymouse class object creation to give ease of writing less code and to save time

[android] Android setOnClickListener method - How does it work?

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