Android back key monitoring

Method 1: Callback method onBackPressed

String LOG_TAG="TAG";
  @Override
    public void onBackPressed() {
    
    
        // super.onBackPressed();//注释掉这行,back键不退出activity

        Log.i(LOG_TAG, "onBackPressed");
    }
这个方法可以阻止用户点击后退键来退出程序。
一般的像升级程序或者重要数据传输页面都是要阻止用户轻易退出的。
这个方法也是我们最简单、常用的一个方法。
方法2：回调方法onKeyDown

```javascript
@Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
    
    
        Log.i(LOG_TAG, "onKeyDown: keyCode -- " + keyCode);

        switch (keyCode) {
    
    
            case KeyEvent.KEYCODE_BACK:
                Log.i(LOG_TAG, "KeyEvent.KEYCODE_BACK");
//                break;
                return false;//拦截事件
            case KeyEvent.KEYCODE_MENU:
                Log.i(LOG_TAG, "KeyEvent.KEYCODE_MENU");
                break;
            case KeyEvent.KEYCODE_HOME:
                Log.i(LOG_TAG, "KeyEvent.KEYCODE_HOME");
                // 收不到
                break;
            case KeyEvent.KEYCODE_APP_SWITCH:
                Log.i(LOG_TAG, "KeyEvent.KEYCODE_APP_SWITCH");
                // 收不到
                break;
            default:
                break;
        }

        return super.onKeyDown(keyCode, event);

    }

This method listens for key events, but blocks the user's behavior, and this method cannot listen for Home button events.

Method 3: The callback method dispatchKeyEvent
can be used when your onBackPressed and onKeyDown fail, dispatchKeyEvent (when onBackPressed and onKeyDown fail, it should be because there is a webview control nested in the activity)

@Override
    public boolean dispatchKeyEvent(KeyEvent event) {
    
    
        Log.i(LOG_TAG, "dispatchKeyEvent: keyCode -- " + event.getKeyCode());
        if (event.getKeyCode()==4){
    
    //回退键的KeyCode是4.
            return false;//表示不分发
        }else{
    
    
            return super.dispatchKeyEvent(event);
        }

    }

This is an event distribution method. This method will be triggered whether the finger presses the screen, slides the screen, or leaves the screen.