我可以使用 android:onClick 按钮属性调用方法名称“onClick”或“onclick”吗？

Question

Xml File:

 <RelativeLayout 
        xmlns:android="http:// schemas.android.com/apk/res/android"
        xmlns:app="http:// schemas.android.com/apk/res-auto"
        xmlns:tools="http:// schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.example.sample.MainActivity" > 
      
        <Button 
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/button_send"
            android:onClick="onClick"/> 
    </RelativeLayout>

Java File:

MainActivity.java:
public class MainActivity extends AppCompatActivity{
  
    @Override
    protected void onCreate(Bundle savedInstanceState) 
    { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.activity_main);
    } 

    public void onClick(View view) 
    { 
        switch (view.getId()) { 
        case R.id.button_send: 
            // Do something 
        } 
    } 
}

So can I call a method named "onClick" or "onclick" using android:onClick attribute?

And how exactly this method works?

Answer 1

Of course you can. In the XML file, android:onClick="onClick" denotes the function name 'onClick' which should run when the button is clicked. As you have defined the function in your java file, there should not be any issues.

Answer 2

Yes, you can. Create a method with any name and provide an object of View class as a formal parameter. Write the code inside this method which you want to be executed when the user clicks the button. In the design window, if you click on the desired button, you will find the onClick option in the right pane. Click on the drop down arrow beside it and you can see the list of methods that can be called when you press the button. Select the desired method. Alternatively, you can directly type the method name over there.

Answer 3

Yes.

When the user clicks a button, the Button object receives an on-click event.

To define the click event handler for a button, add the android:onClick attribute to the element in your XML layout. The value for this attribute must be the name of the method you want to call in response to a click event. The Activity hosting the layout must then implement the corresponding method.

    /** Called when the user touches the button */
    public void sendMessage(View view) {
        // Do something in response to button click
    }

The method you declare in the android:onClick attribute must have a signature exactly as shown above. Specifically, the method must:

1. Be public
2. Return void
3. Define a View as its only parameter (this will be the View that was clicked)

Source: https://developer.android.com/guide/topics/ui/controls/button