XML onClickListener与程序设计方法的优缺点

Question

I would like to find which approach is better for binding onClickListener in Android.

There are several major ways to achieve this. We can use android:onClick attribute in XML , a programmatic approach:

   findViewById(R.id.button1).setOnClickListener(
       new View.OnClickListener() {
          @Override
          public void onClick(View v) {
             //Add some logic
          }
       }
   );

And various DataBinding libraries like ButterKnife . For the sake of simplicity let's leave the data binding libraries aside and focus on the XML attribute VS programmatic approach.

In my opinion, the XML attribute is superior for the following reasons:

1. With the programmatic approach we always have to specify an ID for our elements, but with XML attribute it can be omitted.
2. With the programmatic approach class we have to actively search for the element inside of the view ( findViewById portion), but with the XML attribute, Android does it for us.
3. The programmatic approach class requires at least five lines of code, as we can see, but with the XML attribute, three lines of code are sufficient.
4. With the programmatic approach we have to name our method onClick , but with the XML attribute, we can add any name we want, which will dramatically help with the readability of the code.
5. The XML onClick attribute has been added by Google in the API level 4 release, which means that it is a bit more modern. And the new syntax is almost always better.

Obviously, we cannot use the XML attribute with Fragments, but as far as the Activities go, it looks like a superior approach to me.

That said, in my experience, the programmatic approach seems to be preferred. Am I missing something?

Answer 1

I prefer much more the programmatic approach for two reasons:

Centralized management of the click events : in this case you must use the same method to manage all clicks, instead of a custom method that you can change. Example:

public class ActivityA extends Activity implements View.OnClickListener {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        findViewById(R.id.first).setOnClickListener(this);
        findViewById(R.id.second).setOnClickListener(this);
        findViewById(R.id.third).setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.first:
                // Manage click.
                break;

            case R.id.second:
                // Manage click.
                break;

            case R.id.third:
                // Manage click.
                break;
        }
    }
}

Performance : the programmatic approach is more performant than the XML one for two reasons. The first one is that every time that you declare the android:onClick attribute in XML, a new DeclaredOnClickListener will be instantiated. It's more performant to have a shared click listener if you have more than one View in the same tree. The second one is that DeclaredOnClickListener uses reflection internally to invoke your method.

Same pattern across different components : you can't use the XML approach in a Fragment so you must change the way you declare click listener from Activity to Fragment . Instead, if you use the programmatic approach, you apply the same pattern both in Activity and Fragment .

I'll share also my personal experience: in the past, at the first times, I used also the XML approach. Now, I never use it for a project, because, also if you write more code in the programmatic approach, I think it's more ordered.

Answer 2

Use DataBinding library so that you don't need to call findViewById(int) for each view repeatedly. A public final field will be generated for each View with an ID in the layout. The binding does a single pass on the View hierarchy, extracting the Views with IDs. This mechanism can be faster than calling findViewById(int) for several Views.

MainActivityBinding binding = MainActivityBinding.inflate(getLayoutInflater());

setup clickListener for necessary views as follows.

binding.button1.setOnClickListener(this);
binding.button2.setOnClickListener(this);

Handle all button click events with in the onClick(View) implementation so that you don't need to add individual anonymous listener for each button. Anonymous inner classes should be avoided where ever possible because anonymous classes will hold an implicit reference to the outer class.

 @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.button1:
               onClickButton1();
                break;

            case R.id.button2:
               onClickButton2();
                break;


        }
    }

So we can conclude that the programmatic approach with Data binding seems to be preferred.

Answer 3

Xml approach vs programmatic approach:

pros using xml approach

• on every element you can define a user defined method
• user defined method will have a fully qualified name
• declaring method with fully qualified name improves readability

pros using programmatic approach

• for every "onclick" event of each element you don't have to define a method
• in programmatic approach this can be achieved by declaring only one onclick method by overriding View.OnClickListener

conclusion : It totally depends on developer and requirements-

if there are too many on click methods in one activity than one can choose programmatic approach as it will be very tedious to follow xml approach and write too many on click methods for every element.

Also, if the no. of onclick is not very much in an activity than its a commonsense to use xml approach as there will not be too many methods to write and it will increase readability of code.

xml approach example :

main.xml :

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="92dp"

        android:onClick="clickFunc1"

        android:text="Click me" />
           <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="92dp"

        android:onClick="clickFunc2"

        android:text="Click me" />

</RelativeLayout

MainActivity.java :

public class MainActivity extends Activity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    public void clickFunc1(View view){
        Toast.makeText(MainActivity.this, "Button1 Clicked",    Toast.LENGTH_SHORT).show();
    }

    public void clickFunc2(View view){
        Toast.makeText(MainActivity.this, "Button2 Clicked",    Toast.LENGTH_SHORT).show();
    }


}

programmatic approach :

main.xml :

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="92dp"
        android:text="Click me" />
           <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="92dp"
        android:text="Click me" />
           <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="92dp"
        android:text="Click me" />

</RelativeLayout>

MainActivity.java :

public class MainActivity extends Activity implements View.OnClickListener {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        findViewById(R.id.button1).setOnClickListener(this);
        findViewById(R.id.button2).setOnClickListener(this);
        findViewById(R.id.button3).setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.button1:
               Toast.makeText(MainActivity.this, "Button1 Clicked", Toast.LENGTH_SHORT).show();
                break;

            case R.id.button2:
               Toast.makeText(MainActivity.this, "Button2 Clicked", Toast.LENGTH_SHORT).show();
                break;

            case R.id.button3:
              Toast.makeText(MainActivity.this, "Button3 Clicked",  Toast.LENGTH_SHORT).show();
                break;
        }
    }
}