Detect delete button in soft keyboard

问题:

I have two EditText (each only only accepts one character) and I want to handle both fields like I had only one.

I'm using a TextWatcher to set the focus in the second one when the user writes a character in the first one, but I don't know how to do the opposite.

If the user press the delete button in the second EditText (being this EditText empty) I want to move the focus to the first EditText and delete the character there.

The problem is that TextWatcher doesn't work when the user tries to delete an empty field (because in fact nothing is changing). And onKeyDown event only works with hard keyboards so I don't have any idea of how to deal with this problem...

Thanks!

回答1:

Possible duplicate of Android EditText delete(backspace) key event

just checked the code from that question (which actually come from the provided question and answered by Labeeb P) with the test project with just two edits on layout and it seems to work just fine - I'm able to receive delete even if edit is empty.

    final EditText edit1 = (EditText) findViewById(R.id.editText1);

    edit1.setOnKeyListener(new View.OnKeyListener() {
        @Override
        public boolean onKey(View v, int keyCode, KeyEvent event) {
            // You can identify which key pressed buy checking keyCode value
            // with KeyEvent.KEYCODE_
            if (keyCode == KeyEvent.KEYCODE_DEL) {
                // this is for backspace
                Log.e("IME_TEST", "DEL KEY");
            }
            return false;
        }
    });

Seems android documentation of EditText should be made more clear or at least any guide for EditText - Soft Keyboard interaction provided, because there many typical ones whose should be worked out by nearly every developer.

UPDATE: Seems this way doesn't work on latest (at least after 4.1) Android versions. This answer seems to work on versions after 4.1.

回答2:

A simpler solution to this that I stumbled upon is using an InputFilter. InputFilter's filter() method appears to report all soft keyboard events - even those where the EditText's value isn't changing.

So to address your specific situation, construct an input filter and set accordingly:

private InputFilter filter = (charSequence, start, end, dest, dStart, dEnd) -> {

    if (end == 0 || dStart < dEnd) {
        // backspace was pressed! handle accordingly
    }

    return charSequence;
};

...

myEditText.setFilters(new InputFilter[] { filter });

Backspace events can be evaluated using end, dStart, and dEnd. dStart will always be less than dEnd if a character was deleted. If the EditText is empty, you can still evaluate backspace presses by checking if end == 0.

Note that bulk deletes will also be caught in this if statement, so you may want to do some extra checking withing filter(). Also note that if you're using your computer keyboard to type into EditTexts in emulators, you can get unexpected results. Best to click software buttons for testing.

回答3:

Use the Extension provided at, https://github.com/ciasaboark/Android-Shell/blob/master/src/com/example/com/programmingthetux/tutorial/ZanyEditText.java

import java.util.Random;

import android.content.Context;
import android.util.AttributeSet;
import android.view.KeyEvent;
import android.view.inputmethod.EditorInfo;
import android.view.inputmethod.InputConnection;
import android.view.inputmethod.InputConnectionWrapper;
import android.widget.EditText;
/**
 * Created by mkallingal on 4/25/2016.
 */
public class CustomEditText extends EditText {

    private Random r = new Random();

    public CustomEditText(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public CustomEditText(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public CustomEditText(Context context) {
        super(context);
    }

    public void setRandomBackgroundColor() {

    }

    @Override
    public InputConnection onCreateInputConnection(EditorInfo outAttrs) {
        return new ZanyInputConnection(super.onCreateInputConnection(outAttrs),
                true);
    }

    private class ZanyInputConnection extends InputConnectionWrapper {

        public ZanyInputConnection(InputConnection target, boolean mutable) {
            super(target, mutable);
        }

        @Override
        public boolean sendKeyEvent(KeyEvent event) {
            if (event.getAction() == KeyEvent.ACTION_DOWN
                    && event.getKeyCode() == KeyEvent.KEYCODE_DEL) {
                CustomEditText.this.setRandomBackgroundColor();
                // Un-comment if you wish to cancel the backspace:
                // return false;
            }
            return super.sendKeyEvent(event);
        }


        @Override
        public boolean deleteSurroundingText(int beforeLength, int afterLength) {
            // magic: in latest Android, deleteSurroundingText(1, 0) will be called for backspace
            if (beforeLength == 1 && afterLength == 0) {
                // backspace
                return sendKeyEvent(new KeyEvent(KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_DEL))
                        && sendKeyEvent(new KeyEvent(KeyEvent.ACTION_UP, KeyEvent.KEYCODE_DEL));
            }

            return super.deleteSurroundingText(beforeLength, afterLength);
        }

    }
}

Now you can use it in your Activity like so:

final CustomEditText _EditText = new CustomEditText(_Context);

     _EditText.setOnKeyListener(new View.OnKeyListener() {
                    @Override
                    public boolean onKey(View v, int keyCode, KeyEvent event) {
                        if (keyCode == KeyEvent.KEYCODE_DEL) {
                            String _text=_EditText.getText().toString();
                            if(StringUtils.isBlank(_text))
                                 //EditText is now empty
                            }
                        }
                        return false;
                    }
                });

回答4:

I achieved it by overriding EditText in order to get access to InputConnection object which contains deleteSurroundingText method. It helps to detect deletion (backspace) event. Please, take a look at a solution I provided there: Android - cannot capture backspace/delete press in soft. keyboard

This solution works properly for both hardKeyboard and softKeyboard.