由于最近小蔡的手机音量键坏了，调节音量有点麻烦，突发奇想，想自己实现一个快捷键来调节音量。在忘上参考了一些代码，总结出一般本章，分享给大家。

首先 按钮要想实现悬浮在任何界面，那么必须是要写在服务里面的，使用定时器，2.5s不触摸后，背景变淡

下载地址

清单文件中加权限

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

public class FloatViewService extends Service {

    private static final String TAG = "FloatViewService";
    // 定义浮动窗口布局
    private LinearLayout mFloatLayout;
    private WindowManager.LayoutParams wmParams;
    // 创建浮动窗口设置布局参数的对象
    private WindowManager mWindowManager;

    private ImageButton mFloatView;
    private int screenHeight;
    private int screenWidth;
    private MyCountDownTimer myCountDownTimer;

    @Override
    public void onCreate() {
        super.onCreate();
        Log.i(TAG, "onCreate");
        screenHeight = ScreenParam.getInstance().height;//自己写的工具类用来获取屏幕宽高。
        screenWidth = ScreenParam.getInstance().width;
        createFloatView();
        myCountDownTimer = new MyCountDownTimer(2500, 1000); //设置计时2.5s
        myCountDownTimer.start();
    }

    @SuppressWarnings("static-access")
    @SuppressLint("InflateParams")
    private void createFloatView() {
        wmParams = new WindowManager.LayoutParams();
        // 通过getApplication获取的是WindowManagerImpl.CompatModeWrapper
        mWindowManager = (WindowManager) getApplication().getSystemService(
                getApplication().WINDOW_SERVICE);
        // 设置window type
        wmParams.type = LayoutParams.TYPE_PHONE;
        // 设置图片格式，效果为背景透明
        wmParams.format = PixelFormat.RGBA_8888;
        // 设置浮动窗口不可聚焦（实现操作除浮动窗口外的其他可见窗口的操作）
        wmParams.flags = LayoutParams.FLAG_NOT_FOCUSABLE;
        // 调整悬浮窗显示的停靠位置为右侧底部
        wmParams.gravity = Gravity.RIGHT | Gravity.BOTTOM;
        // 以屏幕左上角为原点，设置x、y初始值，相对于gravity
        wmParams.x = 0;
        wmParams.y = 150;
        // 设置悬浮窗口长宽数据
        wmParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
        wmParams.height = WindowManager.LayoutParams.WRAP_CONTENT;

        LayoutInflater inflater = LayoutInflater.from(getApplication());
        // 获取浮动窗口视图所在布局
        mFloatLayout = (LinearLayout) inflater.inflate(
                R.layout.alert_window_menu, null);
        // 添加mFloatLayout
        mWindowManager.addView(mFloatLayout, wmParams);
        // 浮动窗口按钮
        mFloatView = (ImageButton) mFloatLayout
                .findViewById(R.id.alert_window_imagebtn);

        mFloatLayout.measure(View.MeasureSpec.makeMeasureSpec(0,
                View.MeasureSpec.UNSPECIFIED), View.MeasureSpec
                .makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));

        // 设置监听浮动窗口的触摸移动
        mFloatView.setOnTouchListener(new OnTouchListener() {

            boolean isClick;
            private int leftDistance;
            private float rawX;
            private float rawY;

            @SuppressLint("ClickableViewAccessibility")
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    mFloatLayout.setAlpha(1.0f);
                    myCountDownTimer.cancel();取消计时
                    
                    rawX = event.getRawX();
                    rawY = event.getRawY();
                    break;
                case MotionEvent.ACTION_MOVE:
                    // getRawX是触摸位置相对于屏幕的坐标，getX是相对于按钮的坐标
                    int distanceX = (int) (event.getRawX()-rawX);
                    int distanceY = (int) (event.getRawY()-rawY);
                    leftDistance = (int) event.getRawX()
                            + mFloatView.getMeasuredWidth() / 2;
                    
                    wmParams.x = wmParams.x-distanceX;
                    wmParams.y = wmParams.y-distanceY;
                    // 刷新
                    mWindowManager.updateViewLayout(mFloatLayout, wmParams);
                    rawX = event.getRawX();
                    rawY = event.getRawY();
                    break;
                case MotionEvent.ACTION_UP:
                    
                    myCountDownTimer.start();重新开始计时
                    if(wmParams.x>leftDistance){
                        wmParams.x = screenWidth-mFloatView.getMeasuredWidth() / 2;
                    }else{
                        wmParams.x = 0;
                    }
                    mWindowManager.updateViewLayout(mFloatLayout, wmParams);
                    break;
                }
                return false;
            }
        });

        mFloatView.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                AudioManager audioManager = (AudioManager) getSystemService(Service.AUDIO_SERVICE);
                audioManager.setStreamVolume(AudioManager.STREAM_MUSIC,
                        audioManager.getStreamVolume(AudioManager.STREAM_MUSIC), AudioManager.FLAG_SHOW_UI);
//                Toast.makeText(FloatViewService.this, "hello!",
//                        Toast.LENGTH_SHORT).show();
            }
        });
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if (mFloatLayout != null) {
            // 移除悬浮窗口
            mWindowManager.removeView(mFloatLayout);
        }
    }

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
    
    public class MyCountDownTimer extends CountDownTimer {

        public MyCountDownTimer(long millisInFuture, long countDownInterval) {
            super(millisInFuture, countDownInterval);
        }

        @Override
        public void onTick(long millisUntilFinished) {
        }

        @Override
        public void onFinish() {
            mFloatLayout.setAlpha(0.4f);
        }
    }

}

然后再Activity里启动服务就好了

   protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ScreenParam.getInstance().init(this);
    }
    
    @Override
    protected void onStart() {
        // TODO Auto-generated method stub
         Intent intent = new Intent(MainActivity.this, FloatViewService.class);  
         //启动FloatViewService  
         startService(intent);  
        super.onStart();
    }

如果不想显示Activity界面的话，可以在配置这个属性就ok了

android:theme="@android:style/Theme.NoDisplay"

就是这么简单！