Android随手记：Android系统onKeyDown监控/拦截/监听/屏蔽返回键、菜单键和Home键

在Android系统中用来显示界面的组件（Component）为Activity，也就是说只有重写Activity的onKeyDown方法来监控/拦截/屏蔽系统的返回键（back）、菜单键（Menu）及Home键。

1、拦截/屏蔽返回键、菜单键实现代码

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if(keyCode == KeyEvent.KEYCODE_BACK) { //监控/拦截/屏蔽返回键
        processExit();
return true;
} else if(keyCode == KeyEvent.KEYCODE_MENU) {
//监控/拦截菜单键
} else if(keyCode == KeyEvent.KEYCODE_HOME) {
//由于Home键为系统键，此处不能捕获，需要重写onAttachedToWindow()
}
return super.onKeyDown(keyCode, event);
}
2、拦截/屏蔽系统Home键
public void onAttachedToWindow() {
this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);
super.onAttachedToWindow();
}
为什么必须重写onAttachedToWindow()，看看下面的代码就知道了
/frameworks/policies/base/phone/com/android/internal/policy/impl/PhoneWindowManager.java 1000行附近
if (code == KeyEvent.KEYCODE_HOME) {
// If a system window has focus, then it doesn't make sense  
// right now to interact with applications.  
    WindowManager.LayoutParams attrs = win != null ? win.getAttrs() : null;
if (attrs != null) {
final int type = attrs.type;
if (type == WindowManager.LayoutParams.TYPE_KEYGUARD
|| type == WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG) {
// the "app" is keyguard, so give it the key  
return false;
}
final int typeCount = WINDOW_TYPES_WHERE_HOME_DOESNT_WORK.length;
for (int i=0; i<typeCount; i++) {
if (type == WINDOW_TYPES_WHERE_HOME_DOESNT_WORK[i) {
// don't do anything, but also don't pass it to the app  
return true;
}
}
}
}
当然，重写View的onKeyDown也可以实现，但View如果没有获得焦点，那就不能监控/拦截返回键、菜单键和Home键