[java] Android: how to handle button click

Having a solid experience in non-Java and non-Android area, I'm learning Android.

I have a lot of confusion with different areas, one of them is how to handle button clicks. There are at least 4 way of doing that (!!!), they are briefly listed here

for consistency purpose I will list them:

1. Have a member of the View.OnClickListener class in the activity and assign it to an instance that will handle onClick logic in the onCreate activity method.

2. Create 'onClickListener' in the 'onCreate' activity method and assign it to the button using setOnClickListener

3. Implement 'onClickListener' in activity itself and assign 'this' as a listener for the button. For the case if activity has few buttons, button id should be analyzed to execute 'onClick' handler for the proper button

4. Have public method on the activity that implements 'onClick' logic and assign it to the button in the activity xml declaration

Question #1:

Are those all methods, is there any other option? (I don't need any other, just curious)

For me, the most intuitive way would be the latest one: it requires the least amount of code to be typed and is the most readable (at least for me).

Though, I don't see this approach used widely. What are cons for using it?

Question #2:

What are pros/cons for each of these methods? Please share either your experience or a good link.

Any feedback is welcome!

P.S. I've tried to Google and find something for this topic, but the only things I've found are description "how" to do that, not why is it good or bad.

Step 1:Create an XML File:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:id="@+id/btnClickEvent"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click Me" />
</LinearLayout>

Step 2:Create MainActivity:

package com.scancode.acutesoft.telephonymanagerapp;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity implements View.OnClickListener {

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

        btnClickEvent = (Button) findViewById(R.id.btnClickEvent);
        btnClickEvent.setOnClickListener(MainActivity.this);

    }

    @Override
    public void onClick(View v) {
        //Your Logic
    }
}

HappyCoding!

My sample, Tested in Android studio 2.1

Define button in xml layout

<Button
    android:id="@+id/btn1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

Java pulsation detect

Button clickButton = (Button) findViewById(R.id.btn1);
if (clickButton != null) {
    clickButton.setOnClickListener( new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            /***Do what you want with the click here***/
        }
    });
}

Question#1 - These are the only way to handle view clicks.

Question#2 -
Option#1/Option#4 - There's not much difference between option#1 and option#4. The only difference I see is in one case activity is implementing the OnClickListener, whereas, in the other case, there'd be an anonymous implementation.

Option#2 - In this method an anonymous class will be generated. This method is a bit cumborsome, as, you'd need to do it multiple times, if you have multiple buttons. For Anonymous classes, you have to be careful for handling memory leaks.

Option#3 - Though, this is a easy way. Usually, Programmers try not to use any method until they write it, and hence this method is not widely used. You'd see mostly people use Option#4. Because it is cleaner in term of code.

To make things easier asp Question 2 stated, you can make use of lambda method like this to save variable memory and to avoid navigating up and down in your view class

//method 1
findViewById(R.id.buttonSend).setOnClickListener(v -> {
          // handle click
});

but if you wish to apply click event to your button at once in a method.

you can make use of Question 3 by @D. Tran answer. But do not forget to implement your view class with View.OnClickListener.

In other to use Question #3 properly

Option 1 and 2 involves using inner class that will make the code kind of clutter. Option 2 is sort of messy because there will be one listener for every button. If you have small number of button, this is okay. For option 4 I think this will be harder to debug as you will have to go back and fourth the xml and java code. I personally use option 3 when I have to handle multiple button clicks.

Most used way is, anonymous declaration

    Button send = (Button) findViewById(R.id.buttonSend);
    send.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // handle click
        }
    });

Also you can create View.OnClickListener object and set it to button later, but you still need to override onClick method for example

View.OnClickListener listener = new View.OnClickListener(){
     @Override
        public void onClick(View v) {
            // handle click
        }
}   
Button send = (Button) findViewById(R.id.buttonSend);
send.setOnClickListener(listener);

When your activity implements OnClickListener interface you must override onClick(View v) method on activity level. Then you can assing this activity as listener to button, because it already implements interface and overrides the onClick() method

public class MyActivity extends Activity implements View.OnClickListener{


    @Override
    public void onClick(View v) {
        // handle click
    }


    @Override
    public void onCreate(Bundle b) {
        Button send = (Button) findViewById(R.id.buttonSend);
        send.setOnClickListener(this);
    }

}

(imho) 4-th approach used when multiple buttons have same handler, and you can declare one method in activity class and assign this method to multiple buttons in xml layout, also you can create one method for one button, but in this case I prefer to declare handlers inside activity class.

There are also options available in the form of various libraries that can make this process very familiar to people that have used other MVVM frameworks.

https://developer.android.com/topic/libraries/data-binding/

Shows an example of an official library, that allows you to bind buttons like this:

<Button
    android:text="Start second activity"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="@{() -> presenter.showList()}"
/>

#1 I use the last one frequently when having buttons on the layout which are not generated (but static obviously).

If you use it in practice and in a business application, pay extra attention here, because when you use source obfuscater like ProGuard, you'll need to mark these methods in your activity as to not be obfuscated.

For archiving some kind of compile-time-security with this approach, have a look at Android Lint (example).

#2 Pros and cons for all methods are almost the same and the lesson should be:

Use what ever is most appropriate or feels most intuitive to you.

If you have to assign the same OnClickListener to multiple button instances, save it in the class-scope (#1). If you need a simple listener for a Button, make an anonymous implementation:

button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        // Take action.
    }
});

I tend to not implement the OnClickListener in the activity, this gets a little confusing from time to time (especially when you implement multiple other event-handlers and nobody knows what this is all doing).

I prefer option 4, but it makes intuitive sense to me because I do far too much work in Grails, Groovy, and JavaFX. "Magic" connections between the view and the controller are common in all. It is important to name the method well:

In the view,add the onClick method to the button or other widget:

    android:clickable="true"
    android:onClick="onButtonClickCancel"

Then in the class, handle the method:

public void onButtonClickCancel(View view) {
    Toast.makeText(this, "Cancel pressed", Toast.LENGTH_LONG).show();
}

Again, name the method clearly, something you should do anyway, and the maintenance becomes second-nature.

One big advantage is that you can write unit tests now for the method. Option 1 can do this, but 2 and 3 are more difficult.