确定按“退格”按钮

Question

如何在GWT中确定用户按下 Backspace 按钮？我试过这个，但它不起作用

  @Override
  public void onKeyPress(KeyPressEvent event) {
       char charCode= event.getCharCode();
       if(charCode == (char) KeyCodes.KEY_BACKSPACE){
           //do someThing 
       }
  }

Answer 1

keypress事件在大多数浏览器中实现为仅在生成角色时触发（这就是它的标准化方式：http://www.w3.org/TR/DOM-Level-3-Events/#event-type-keypress）。退格显然不会产生一个角色;您应该使用keydown或keyup来检测它。

Answer 2

您可以从一个完全不同的角度思考它，只需跟踪输入TextBox的字符串的长度或您想要从中获取文本的任何内容：

        // Global variable to save previous String data
        String stringEntered = "";

        // Our TextBox
        TextBox textBox = new TextBox();

        @Override
        public void onKeyPress(KeyPressEvent event) {

            if(stringEntered.length() > textBox.getValue().length()) {
                // At this point we know that a character has been deleted, 
                   so we can clear a list or reset something accordingly
                ...
            }

Answer 3

@Override
public void onKeyPress(KeyPressEvent event) {
   char charCode= event.getCharCode();
   if(charCode == (char) KeyEvent.VK_BACK_SPACE){
       //do someThing 
   }
}

Answer 4

    @Override
    public void onKeyPress(KeyUpEvent event) {
       char charCode= keyUpEvent.getNativeKeyCode();
       if(charCode == (char) KeyCodes.KEY_BACKSPACE){
           //do someThing 
    }