一、重写方法，处理对应的按键回调事件

当处理物理按钮事件的时候提供的回调方法有

• onKeyDown()
• onKeyUp()
• onKeyLongPress()

如下是例子：返回键被按下，提示退出程序

public class MainActivity extends Activity {
    private long exitTime = 0; //退出时间变量值
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            exit();
            return true;  //拦截返回键
        }
        return super.onKeyDown(keyCode, event);
    }
    
    public void exit() {
        if ((System.currentTimeMillis() - exitTime) > 2000) { //计算按键时间差是否大于两秒
            Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();
            exitTime = System.currentTimeMillis();
        } else {
            finish();
            System.exit(0); //销毁强制退出
        }
    }
}

二、键值

三、framework按键消息派发

按键消息派发(android 4.2(jb5))

frameworks/base/policy/src/com/android/internal/policy/impl/PhoneWindowManager.java
  dispatchUnhandledKey
        interceptFallback
            interceptKeyBeforeQueueing [interceptKeyTq]
            interceptKeyBeforeDispatching [interceptKeyTi]

四、增加一个按键

底层抓键值:adb shell getevent /dev/input/event0
adb shell getevent /dev/input/event1
0001 012c 00000001 : 十六进制，012c=300

先用adb shell getevent,可以看到选项，后面的是可以选的

增加一个按键([android 5.1，6.0])

alps/device/xxx/xxx/mtk-kpd.kl
 key 300   FM

alps/frameworks/native/include/android/keycodes.h
  AKEYCODE_FM  = 300,//added for fm

alps/frameworks/native/include/input/InputEventLabels.h
static const InputEventLabel KEYCODES[] = {
    // added for fm
    DEFINE_KEYCODE(FM), //= {"FM",AKEYCODE_FM}
}

//注：宏定义函数#define DEFINE_KEYCODE(key) { #key, AKEYCODE_##key } = {"key", AKEYCODE_key}
//#是把宏参数变为一个字符串，##是把两个宏参数连接在一起

alps/frameworks/base/core/java/android/view/KeyEvent.java
    /**
     * @hide
     */
    public static final int KEYCODE_FM            = 300;
    //added for fm
    private static final int LAST_KEYCODE = KEYCODE_FM;//modify for fm