上一篇文章Framework學習（十一）WindowManager體系我們分析了WindowManager的用法及原始碼，這篇文章我們使用WindowManager實現一個簡單的懸浮窗效果。

類似與下面這種效果：

專案目錄

專案目錄結構很簡單，一個MainActivity，一個WindowService。MainActivity只有兩個按鈕，用於啟動和關閉WindowService。新增實現懸浮窗的邏輯全部放在WindowService中。

還有兩個xml檔案，一個是MainActivity佈局，只有兩個Button，一個是懸浮窗佈局，只有一個TextView，TextView添加了一個圓形背景。

懸浮窗背景用shape實現，放在drawable資料夾下。

專案程式碼

直接上程式碼吧：

MainActivity

public class MainActivity extends AppCompatActivity {
    private Button startService;
    private Button stopService;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        startService = (Button) findViewById(R.id.start);
        stopService = (Button) findViewById(R.id.stop);

        startService.setOnClickListener(new
 
 View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent it = new Intent(MainActivity.this, WindowService.class);
                startService(it);
            }
        });

        stopService.setOnClickListener(new View.OnClickListener() {
            @Override
 

            public void onClick(View view) {
                Intent it = new Intent(MainActivity.this, WindowService.class);
                stopService(it);
            }
        });
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.hx.wms.MainActivity">

    <Button
        android:id="@+id/start"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="start service" />

    <Button
        android:id="@+id/stop"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="stop service"
        android:layout_below="@+id/start"/>
</RelativeLayout>

WindowService

public class WindowService extends Service {

    private final String TAG = this.getClass().getSimpleName();

    private WindowManager.LayoutParams wmParams;
    private WindowManager mWindowManager;
    private View mWindowView;
    private TextView mPercentTv;

    private int mStartX;
    private int mStartY;
    private int mEndX;
    private int mEndY;

    @Override
    public void onCreate() {
        super.onCreate();
        Log.i(TAG, "onCreate");
        initWindowParams();
        initView();
        addWindowView2Window();
        initClick();
    }

    private void initWindowParams() {
        mWindowManager = (WindowManager) getApplication().getSystemService(getApplication().WINDOW_SERVICE);
        wmParams = new WindowManager.LayoutParams();
        //type
        wmParams.type = WindowManager.LayoutParams.TYPE_PHONE;
        wmParams.format = PixelFormat.TRANSLUCENT;
        //flags
        wmParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
        wmParams.gravity = Gravity.LEFT | Gravity.TOP;
        wmParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
        wmParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
    }

    private void initView() {
        mWindowView = LayoutInflater.from(getApplication()).inflate(R.layout.layout_window, null);
        mPercentTv = (TextView) mWindowView.findViewById(R.id.percentTv);
    }

    private void addWindowView2Window() {
        mWindowManager.addView(mWindowView, wmParams);
    }
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.i(TAG, "onStartCommand");
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if (mWindowView != null) {
            //移除懸浮視窗
            Log.i(TAG, "removeView");
            mWindowManager.removeView(mWindowView);
        }
        Log.i(TAG, "onDestroy");
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

...

}

在設定各種屬性之後，直接向WindowManager中新增mWindowView（也就是我們自己的佈局layout_window.xml）。

下面我們實現懸浮窗點選和跟著手指拖動的效果，根據拖動距離，判斷是點選還是滑動。由於onTouchEvent()的優先順序比onClick高，拖動時在需要的攔截的地方，return true就行了。具體如下：

   private void initClick() {
        mPercentTv.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        mStartX = (int) event.getRawX();
                        mStartY = (int) event.getRawY();
                        break;
                    case MotionEvent.ACTION_MOVE:
                        mEndX = (int) event.getRawX();
                        mEndY = (int) event.getRawY();
                        if (needIntercept()) {
                            //getRawX是觸控位置相對於螢幕的座標，getX是相對於按鈕的座標
                            wmParams.x = (int) event.getRawX() - mWindowView.getMeasuredWidth() / 2;
                            wmParams.y = (int) event.getRawY() - mWindowView.getMeasuredHeight() / 2;
                            mWindowManager.updateViewLayout(mWindowView, wmParams);
                            return true;
                        }
                        break;
                    case MotionEvent.ACTION_UP:
                        if (needIntercept()) {
                            return true;
                        }
                        break;
                    default:
                        break;
                }
                return false;
            }
        });

        mPercentTv.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (isAppAtBackground(WindowService.this)) {
                    Intent intent = new Intent(WindowService.this, MainActivity.class);
                    intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                    startActivity(intent);
                }
            }
        });
    }

/**
     * 是否攔截
     * @return true:攔截;false:不攔截.
     */
    private boolean needIntercept() {
        if (Math.abs(mStartX - mEndX) > 30 || Math.abs(mStartY - mEndY) > 30) {
            return true;
        }
        return false;
    }


 /**
     *判斷當前應用程式處於前臺還是後臺
     */
    private boolean isAppAtBackground(final Context context) {
        ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
        List<ActivityManager.RunningTaskInfo> tasks = am.getRunningTasks(1);
        if (!tasks.isEmpty()) {
            ComponentName topActivity = tasks.get(0).topActivity;
            if (!topActivity.getPackageName().equals(context.getPackageName())) {
                return true;
            }
        }
        return false;
    }

最後需要在AndroidManifest.xml中註冊Service和新增相應的限權。

<service android:name=".WindowService"/>

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

效果