Best practice for defining button events in android


Answers

Here is the best approach with code:

  public class MyTest extends Activity implements OnClickListener{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
     //... some other code here to init the layout
        Button btn1 = (Button)findViewById(R.id.button1);
        Button btn2 = (Button)findViewById(R.id.button2);
        btn1.setOnClickListener(this);
        btn2.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch(v.getId()){
            case R.id.button1:
                break;
            case R.id.button2:
                break;
        }
    }
}

The new class with an interface is only good if you want to decouple the implementation (when you want to use the same class code somewhere else, move it to another seperate class file etc..) but in general if you are doing things connected with the current activity you are on and the onClick implementations depend on it running with reference to the objects defined there you should definitely use the method i suggested.

Creating class interfaces is only good when you want to achieve communication between seperate classes or activities and keep things apart. other than that its a bad practice creating subclasses for this.

Question

I have a Layout defined in XML which consists of several Buttons.

Currently I am doing this in the OnCreate method to define the event handlers against the buttons:

public void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Button newPicButton = (Button)findViewById(R.id.new_button);
    newPicButton.setOnClickListener(btnListener);
    ..... similarly for other buttons too
    .....
}

Inside of the Button's onClick event, I launch a camera Intent to get a picture and inside the onActivityResult callback I am again setting the event handlers along with setting the View like this:

protected void onActivityResult(int requestCode, int resultCode, Intent data) 
{ 
    setContentView(R.layout.main);
    Button newPicButton = (Button)findViewById(R.id.new_button);
    newPicButton.setOnClickListener(btnListener);
    ...similarly for other buttons too
}

I am new to android and this approach of redefining an event every time seems quite dirty to me. I would like to know what is the best practice in terms of defining button event handlers in scenarios like this.

Edit: pasting my complete class

public class CameraAppActivity extends Activity 
{
    /** Called when the activity is first created. */

    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Button newPicButton = (Button)findViewById(R.id.new_button);
        newPicButton.setOnClickListener(btnListener);
    }

    //---create an anonymous class to act as a button click listener---
    private OnClickListener btnListener = new OnClickListener()
    {

        public void onClick(View v)
        {   
             //Intent newPicIntent = new Intent(v.getContext(), NewPictureActivity.class);
             //startActivityForResult(newPicIntent, 0);
            Intent cameraIntent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
            startActivityForResult(cameraIntent, 999);
        } 

    };  

    protected void onActivityResult(int requestCode, int resultCode, Intent data) 
    {  

        setContentView(R.layout.main);
        Button newPicButton = (Button)findViewById(R.id.new_button);
        newPicButton.setOnClickListener(btnListener);

       //if I comment last two lines nothing happens when I click on button

    }  

The main question is

setContentView(R.layout.main);
Button newPicButton = (Button)findViewById(R.id.new_button);
newPicButton.setOnClickListener(btnListener);

Re-registering events inside onActivityResult.. is it right approach? Or am I doing something wrong? Because If I don't re-register event nothing happens when I click the button.




The problem is the object for the button newPicButton is being created as a local object which is valid only in the scope of the function onCreate and as soon as the code exits that function the garabage collector deallocates the object for the button. what you need to do is declare the newPicButton object outside any method and then in onCreate method assign it a listener. This will solve your problem and i hope i have explained why nothing happens when you remove the code for the newPicButton in the onActivityResult method :)




@Hasan This is the best approach that i have found and which works for me every single time flawlessly.

  • In Layout.xml define the onClick for the button

                    <Button android:id="@+id/Button01"          
                        android:onClick="@string/method" 
                        android:focusable="true" android:clickable="true"
                        ">
                    </Button>
    
  • In the R.string file add the following line

string name="method">buttonFunction

  • In the sample.java file the function define in R.string will be called on the click of the button and it should look something like

    public void buttonFunction(View view) { // do nething u like on the click of the button }




Here is how I did it:

  1. In Buttons XML file set android:onClick="onClick".
  2. In your Activity implement View.OnClickListener.
  3. Inside onClick method use Switch key (as below).

@Override

public void onClick(View view) {
    Intent intent;
    switch(view.getId()){

        case R.id.home_button:
            //DO something
            intent = new Intent(HashTagActivity.this,MainActivity.class);
            startActivity(intent);
            break;
        case R.id.back_button:
            //DO something
             intent = new Intent(HashTagActivity.this,ClassActivity.class);
            startActivity(intent);
            break;
        case R.id.favorite_button:
            //DO something
            break;
        case R.id.copy_button:
            //DO something

            break;

    }
}

It works Great.




There is no best practice defined. It heavily depends on the use case. You could define them in your XML layout using the Button's onClick attribute.

XML example:

<!-- Stuff -->
<Button android:id="@+id/my_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Click Me!"
    android:onClick="myClickMethod" />

Java example:

// stuff
public void myClickMethod(View v) {
    // more stuff
}

That way you don't have to implement the OnClickListener yourself. You can assign each Button the same onClick method and then simply decide on a per-view basis what action to trigger or you can have a separate method for every Button.

In general I advice against using one OnClickListener for more than one Button. It is easier to understand what each listener is supposed to do if you use descriptive names which is what you should do anyway.




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