Best way to implement View.OnClickListener in android

Question

Suppose we have an Activity with a lot of views on which OnClickListener is to be registered.

The most common way to implement this is to let the Activity-Subclass implement the OnClickListener, something like this:

public class ActivityMain extends Activity implements View.OnClickListener
{   
    @Override
    public void onClick(View view)
    {
        switch (view.getId())
        {
            //handle multiple view click events
        }
    }
}

The way i like to implement it is to create a private class inside the Activity-Subclass and let that inner class implement the OnClickListener:

public class ActivityMain extends Activity implements View.OnClickListener
{
    private class ClickListener implements View.OnClickListener
    {   
        @Override
        public void onClick(View view)
        {
            switch (view.getId())
            {
                //handle multiple view click events
            }
        }
    }
}

This way the code seems more organized and easy to maintain.

Moreover, talking about "Is-a", "Has-a" relationships, the latter seems to be a good practice because now the Activity-Subclass would have a "Has-a" relationship with the ClickListener. While in the former method we would be saying that Our Activity-Subclass "Is-a" ClickListener, which ain't completely true.

Note that, i am not concerned with the memory overhead the latter would cause.

Also, adding onClick tag in xml is completely out of question.

So, what really is the best way to implement a ClickListener?

Please don't suggest any libraries like RoboGuice or ButterKnife etc.

UPDATE:

I would like to share the approach I finally adopted.

I directly implement the listener in Activity/Fragment.

As far as OOP design is concerned. The "HAS-A" approach doesn't offers any practical benefits and even takes up more memory. Considering the amount of nested classes(and the memory overhead) we will be creating for every similar listener we implement, this approach should clearly be avoided.

Answer 1

First, there is no best practice defined by Android regarding registering click listeners. It totally depends on your use case.

Implementing the View.OnClickListener interface to Activity is the way to go. As Android strongly recommends interface implementation over and over again whether it is an Activity or Fragment.

Now as you described :

public class ActivityMain extends Activity implements View.OnClickListener
{
    private class ClickListener implements View.OnClickListener
    {   
        @Override
        public void onClick(View view)
        {
            switch (view.getId())
            {
                //handle multiple view click events
            }
        }
    }
}

This is your approach. Now it is your way of implementation and there is nothing wrong with this if you are not concerned with memory overhead. But what's the benefit of creating the inner class and implementing the View.OnClickListener if you can simply implement that in the main class which can also lead to the code clarity and simplicity that you need.

So it just a discussion rather getting the best possible solution of implementing the View.OnClickListener because if you go with the practical point of everyone, you will go for a solution which is simple and memory efficient.

So I would prefer the conventional way. It keeps things simple and efficient. Check the code below:

@Override
public void onClick(View view)
{
    switch (view.getId())
    {
        //handle multiple view click events
    }
}

PS : Your approach will definitely increase lines of code :P ;)

Answer 2

First of all lets get the basics clear here..

By implementing an Interface, your class doesn't become that.. like you said:

"Our Activity-Subclass "Is-a" ClickListener, which ain't completely true."

Your class can only have "Is-a" relationship if it extends, in this case an Activity . Implementing an interface means that it can behave like what interface has set its contract.

An Example:

class Peter extends Human .. means Peter is a Human..

class Peter can also implement programmer, musician, husband etc means Peter can behave as the above.

As for best practice, you could make an entirely separate class which implements OnClickListener like this:

class MyListener implements View.OnClickListener{

  @Override
public void onClick(View view) {
        // do whatever you want here based on the view being passed
    }

}

And in your main Activity you could instantiate MyListener and call onClick() and pass your view in it:

MyListener listener = new MyListener();

Button b = null;

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

    button = (Button)findViewById(R.id.button);
    listener.onClick(button);
   }

Answer 3

I use button.setOnClickListener(this); where my Activity implements View.OnClickListener , and then get the ID of the Button in a separate method. See below for an example:

public class MyActivity extends ActionBarActivity implements View.OnClickListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.YOUR_LAYOUT);

        ...

        Button myFirstButton = (Button) findViewById(R.id.YOUR_FIRST_BUTTON);
        myFirstButton.setOnClickListener(this);

        Button mySecondButton = (Button) findViewById(R.id.YOUR_SECOND_BUTTON);
        mySecondButton.setOnClickListener(this);

        ...

    }

    ...

    @Override
    public void onClick(View v) {
        Button b = (Button) v;
        switch(b.getId()) {
            case R.id.YOUR_FIRST_BUTTON:
                // Do something
                break;
            case R.id.YOUR_SECOND_BUTTON:
                // Do something
                break;
            ...
        }
    }

    ...

}

Answer 4

Here you can create a btnClickListner object and after that you will call that btnCLickLisner object when ever you want to perform the onCLieck actions for buttons..

Let us assume, in my activity i have a 5 to 10 buttons and writing each button separate onclick listner is bad idea. So to over come this,we can use like below..

register your buttons

Button button1 = (Button)findViewById(R.id.button1);
Button button2 = (Button)findViewById(R.id.button2);
Button button3 = (Button)findViewById(R.id.button3);
Button button4 = (Button)findViewById(R.id.button4);
Button button5 = (Button)findViewById(R.id.button5);

Here i am setting the onclick listner to my buttons after click

button1.setOnClickListener(btnClickListner);
button2.setOnClickListener(btnClickListner);
button3.setOnClickListener(btnClickListner);
button4.setOnClickListener(btnClickListner);
button5.setOnClickListener(btnClickListner);

Here is the btnClick Listner implementation

View.OnClickListener btnClickListner = new OnClickListener()
    {
  @Override
        public void onClick( View v )
        {
            // TODO Auto-generated method stub
            if( button1.getId() == v.getId() )
            {
                //Do Button1 click operations here

            }
            else if( button2.getId() == v.getId() )
            {

               // Do Button2 click operations here

            }
            else if( button3.getId() == v.getId() )
            {
                 // Do Button3 click operations here

            }
            else if( button4.getId() == v.getId() )
            {
                // Do Button4 click operations here

            }
            else if( button5.getId() == v.getId() )
            {
                // Do Button5 click operations here
            }

        }

     }

Answer 5

I have found using Butterknife makes for clean code. And because it uses code generation (not reflections) it has little performance overhead.

public class ActivityMain extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      ButterKnife.inject(this);
  }

  @OnClick(R.id.button_foo)
  void onFoodClicked() {
    // Do some foo
  }

  @OnClick(R.id.button_bar)
  void onBarClicked() {
    // do some bar
  }
}

Answer 6

Your ClickListener is an inner non-static class the coupling of this 'has-a' is no different than if your class Activity implemented View.OnClickListener . This is because your inner ClickListener requires an instance of ActivityMain and really can't be reused. I would argue that you're over engineering and aren't actually gaining anything.

EDIT: To answer your question I like to have anonymous View.OnClickListener for each widget. I think this creates the best separation of logic. I also have methods like setupHelloWorldTextView(TextView helloWorldTextView); where I put all my logic related to that widget.

Answer 7

First approach is better than the other because thats why View.OnClickListener is an Interface instead of an abstract class . besides the later might leak in various situations since you are using a non-static inner class.

Answer 8

A small remark to this, and maybe a little bit of topic.

What, if we not just implement OnClickListener and we have a bunch of other Listeners / Callback to implement. In my Opinion it will get messy to implement all of these in the class instead of using anonymous classes / lambda. It is hard to remember wich method belongs to which interface.

So if we have to implement an interface (in this case OnClickListener) multiple times it my be a good solution to implement on class base and use the switch/case.

But if we have to implement multiple interfaces it may be a good solution to use anonymous classes / lambda

Answer 9

For this particular case I'd say that maintain a single instance of a OnClickListener is the best approach for you. You will have a "Has-a" relationship and won't need to create several instances since you are handling the behavior using the view id in the onClick(View view) callback.

public class ActivityMain extends Activity implements View.OnClickListener {

    private View.OnClickListener mClickListener = new View.OnClickListener() {   
        @Override
        public void onClick(View view) {
            switch (view.getId()) {
                //handle multiple view click events
            }
        }
    };

}

Answer 10

simply you using like not implements subclass or not handle a click event just do like this way .

android.view.View.OnClickListener method_name = new android.view.View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            // put your code .
        }
    };

and handle click event into button ya any type of click event like

button_name.setOnClickListener(method_name);

its work very simply Thanks

Answer 11

 public class ProfileDetail extends AppCompatActivity implements View.OnClickListener {

          TextView tv_address, tv_plan;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_profile_detail);



            tv_address = findViewById(R.id.tv_address);
            tv_plan = findViewById(R.id.tv_plan);

            tv_address.setOnClickListener(this);
            tv_plan.setOnClickListener(this);
    }
 @Override
    public void onClick(View view) {
            switch (view.getId()) {
                case R.id.tv_plan:
                    startActivity(new Intent(getApplicationContext(),PlanActivity.class));
                    break;
                case R.id.tv_address:
                     startActivity(new Intent(getApplicationContext(),AddressActivity.class));
                    break;
            }
        }
}

Answer 12

It really depends on what you want to achieve. If you have eg a complex functionality with threading, dependencies, etc., I personally like to decouple it completely from the Activity into a separate class XyzAction , that does the heavy stuff, knows about certain Invoker s and returns them results, if needed. My Invoker s are basically objects, that implement OnClick / OnTouch /etc. Listener s and bind themselves to needed actions. Eg there could be a LoginInvoker implementing OnClickListener for a Button and an ImageView and also a generic ActionListener that gets invoked when a MenuItem is clicked. The Invoker has update methods for showing progress to the user and the result of the bound action. The action posts updates to its Invoker s and can be garbage collected, if all of them die, because it has no connection to the UI.

For less complex actions, I couple them directly to the Android component (ie Activity / Feagment / View ) and also call them Actions , with the big difference of them implementing the UI callbacks directly.

In both cases I declare the actions as members, so I can see on a quick glance what specific actions the Android component supports.

If there's something trivial like "show a Toast if button is pressed", I use anonymous inner classes for the UI callbacks, because you normally don't care that much about them with regards to maintainability.

Answer 13

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
Button north,south,east,west;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    init();
    north.setOnClickListener(this);
    south.setOnClickListener(this);
    east.setOnClickListener(this);
    west.setOnClickListener(this);
}

private void init(){
    north = findViewById(R.id.north);
    south = findViewById(R.id.south);
    east = findViewById(R.id.east);
    west = findViewById(R.id.west);
}

@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.north:
            Toast.makeText(MainActivity.this,"NORTH",Toast.LENGTH_SHORT).show();
            break;
        case R.id.south:
            Toast.makeText(MainActivity.this,"SOUTH",Toast.LENGTH_SHORT).show();
            break;
        case R.id.east:
            Toast.makeText(MainActivity.this,"EAST",Toast.LENGTH_SHORT).show();
            break;
        case R.id.west:
            Toast.makeText(MainActivity.this,"WEST",Toast.LENGTH_SHORT).show();
            break;
    }
  }
}

Answer 14

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private Chronometer chronometer;
    private Button startButton;
    private Button stopButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        chronometer = findViewById(R.id.chronometer);
        startButton =findViewById(R.id.startBtn);
        stopButton = findViewById(R.id.stopBtn);

        startButton.setOnClickListener(this);
        stopButton.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.startBtn:
                chronometer.start();
                break;
            case R.id.stopBtn:`
                chronometer.stop();
                break;

        }
    }

}