Why do you need to pass an object of type View to this method?

Question

<Button
    android:id="@+id/button1"
    style="?android:attr/buttonStyleSmall"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/textView1"
    android:layout_alignParentTop="true"
    android:text="@string/button1" 
    android:onClick="onClickButton"/>


public void onClickButton(View view){


    TextView textview = (TextView) findViewById(R.id.textView1);

    textview.setVisibility(View.VISIBLE);


}

That is the code that makes the text appear in the main activity interface when the button is pressed. What is the point of passing in an View object when you don't use it in the "onClickButton" method block? I am asking this because the app crashes if I leave out the parameter even when I am not using the view object in the code block.

Answer 1

You might have several buttons in your layout, and only one method in your activity's code. In such a situation, it becomes necessary to differentiate between different buttons.

That's where this can be used.

public void onClickButton(View view){
    if(view.getId() == R.id.buttonSave){
        // Do something
    } else if(view.getId() == R.id.buttonCancel){
        // Do something else
    }
}

Although, you can bind different methods to different views, by having a method for each view type.

Yet another use case could be:

After clicking on the button, you want to modify the button itself, say, hide it, or change the label, then you obviously need a reference to the button.

Answer 2

what is the point of passing in an object view of type View when you don't use it in the "onClickButton" method block?

First of all, the Button Docs tell you to. Secondly, it can get used in the function. Since Buttons aren't the only Views which are clickable, having the View parameter allows you to check that View type to see what has been pressed and to perform other operations with it.