Android如何检测按下键盘上的“删除”按钮以删除单个字符？

Question

I'm working on a remote control app and need to detect when a user pressed the <x delete button on an empty text field to send this character over and delete something from a remote machine.

How can I detect that the user pressed <x Delete button on Android keyboard?

I tried to ad on key listener, but that did not seem to work.

final EditText edittext = (EditText) findViewById(R.id.editText);
edittext.setOnKeyListener(new View.OnKeyListener() {
    public boolean onKey(View v, int keyCode, KeyEvent event) {
        // If the event is a key-down event on the "enter" button
        Log.i("KEYCODE", "" + keyCode);
        if ((event.getAction() == KeyEvent.ACTION_DOWN) &&
                (keyCode == KeyEvent.KEYCODE_ENTER)) {
            // Perform action on key press
            return false;
        } else if (edittext.length() == 0) {
            if(keyCode == KeyEvent.KEYCODE_DEL) {
                //perform erase when the text field is empty
            }
        }
        return false;
    }
});

Answer 1

I know I am late, but hope this will help someone else. There is no direct way to do this using a listener, but if you look into the documentation of onTextChanged Listener you will find this:

This method is called to notify you that, within s , the count characters beginning at start have just replaced old text that had length before .

So in case of a backspace you will have this condition:

Within s (the editable view), 0 characters beginning at start (depends where the cursor is) have replaced old text that had length before (it's value will be generally 1, unless user first selected some text and then hit backspace)

So if count == 0 you can assume that delete key was pressed.

Answer 2

You can't use a View.OnKeyListener for software keyboards.

View.OnKeyListener:

Interface definition for a callback to be invoked when a hardware key event is dispatched to this view. This is only useful for hardware keyboards; a software input method has no obligation to trigger this listener .

Source: http://developer.android.com/reference/android/view/View.OnKeyListener.html

Answer 3

Use the method DispatchKeyEvent :

@Override public boolean dispatchKeyEvent(@NonNull KeyEvent event) { 
    if (event.getAction() == KeyEvent.ACTION_DOWN
        && event.getKeyCode() == KeyEvent.KEYCODE_DEL) {
        // ... 
    }
    return super.dispatchKeyEvent(event);
}

(stolen from here)