//布局中就一個(gè)Button
public class MainActivity extends Activity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View view) {
   //目的就是啟動(dòng)Service來打開懸浮窗體
    startService(new Intent(MainActivity.this, FloatService.class));
    finish();
   }
  });

 }
}

/**
 * description：通過Service來開啟FloatView
 * 作者：ldm
 * 時(shí)間：20162016/8/17 14:03
 * 郵箱：1786911211@qq.com
 */
public class FloatService extends Service {
 @Override
 public void onCreate() {
  super.onCreate();
  CustomViewManager.getInstance(this).showFloatViewOnWindow();
 }

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

/**
 * description：
 * 作者：ldm
 * 時(shí)間：20162016/8/17 11:57
 * 郵箱：1786911211@qq.com
 */
public class CustomViewManager {
 //上下文
 private Context mContext;
 //本類實(shí)例
 private static CustomViewManager instance;
 //自定義的FloatView
 private FloatView mFloatView;
 //窗口管理類
 private WindowManager mWindowManager;

 private CustomViewManager(Context context) {
  this.mContext = context;
  mFloatView = new FloatView(mContext);
  mWindowManager = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
 }

 /**
  * @param
  * @description 通過單例模式獲取實(shí)例對(duì)象
  * @author ldm
  * @time 2016/8/17 11:59
  */
 public static CustomViewManager getInstance(Context mContext) {
  if (null == instance) {
   synchronized (CustomViewManager.class) {
    if (null == instance) {
     instance = new CustomViewManager(mContext);
    }
   }
  }
  return instance;
 }

 /**
  * @param
  * @description 在手機(jī)屏幕上顯示自定義的FloatView
  * @author ldm
  * @time 2016/8/17 13:47
  */
 public void showFloatViewOnWindow() {
  WindowManager.LayoutParams parmas = new WindowManager.LayoutParams();
  parmas.width = mFloatView.getFloatWidth();
  parmas.height = mFloatView.getFloatHeight();
  //窗口圖案放置位置
  parmas.gravity = Gravity.LEFT | Gravity.CENTER;
  // 如果忽略gravity屬性，那么它表示窗口的絕對(duì)X位置。
  parmas.x = 0;
  //如果忽略gravity屬性，那么它表示窗口的絕對(duì)Y位置。
  parmas.y = 0;
  ////電話窗口。它用于電話交互（特別是呼入）。它置于所有應(yīng)用程序之上，狀態(tài)欄之下。
  parmas.type = WindowManager.LayoutParams.TYPE_SYSTEM_ALERT;
  //FLAG_NOT_FOCUSABLE讓window不能獲得焦點(diǎn)，這樣用戶快就不能向該window發(fā)送按鍵事件及按鈕事件
  //FLAG_NOT_TOUCH_MODAL即使在該window在可獲得焦點(diǎn)情況下，仍然把該window之外的任何event發(fā)送到該window之后的其他window.
  parmas.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
  // 期望的位圖格式。默認(rèn)為不透明。參考android.graphics.PixelFormat。
  parmas.format = PixelFormat.RGBA_8888;
  mWindowManager.addView(mFloatView, parmas);
 }
}

/**
 * description：
 * 作者：ldm
 * 時(shí)間：20162016/8/17 11:17
 * 郵箱：1786911211@qq.com
 */
public class FloatView extends View {
 //懸浮球?qū)挾?
 private int floatWidth = 150;
 //懸浮球高度
 private int floatHeight = 150;
 //懸浮球畫筆
 private Paint mPaint;
 //繪制文字畫筆
 private Paint mTextPaint;
 private String text = "50%";

 public FloatView(Context context) {
  super(context);
  initPaint();
 }


 public int getFloatWidth() {
  return floatWidth;
 }


 public int getFloatHeight() {
  return floatHeight;
 }

 public FloatView(Context context, AttributeSet attrs) {
  super(context, attrs);
  initPaint();
 }

 public FloatView(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  initPaint();
 }

 /**
  * @param
  * @description 初始化畫筆
  * @author ldm
  * @time 2016/8/17 11:37
  */
 private void initPaint() {
  //設(shè)置懸浮球畫筆
  mPaint = new Paint();
  mPaint.setColor(Color.GREEN);
  mPaint.setAntiAlias(true);
  mPaint.setDither(true);
  //設(shè)置文字畫筆
  mTextPaint = new Paint();
  mTextPaint.setTextSize(25);
  mPaint.setAntiAlias(true);
  mTextPaint.setColor(Color.WHITE);
  mTextPaint.setFakeBoldText(true);
 }

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  //設(shè)置大小
  setMeasuredDimension(floatWidth, floatHeight);
 }

 /**
  * @param
  * @description 繪制圖案
  * @author ldm
  * @time 2016/8/17 11:44
  */
 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  //繪制懸浮球
  canvas.drawCircle(floatWidth / 2, floatHeight / 2, floatWidth / 2, mPaint);
  //繪制文字
  Paint.FontMetrics metrics = mTextPaint.getFontMetrics();
  //文字大小計(jì)算可以參考：http://mikewang.blog.51cto.com/3826268/871765/
  float textWidth = mTextPaint.measureText(text);
  float x = floatWidth / 2 - textWidth / 2;
  float dy = -(metrics.descent + metrics.ascent) / 2;
  float y = floatHeight / 2 + dy;
  canvas.drawText(text, x, y, mTextPaint);
 }
}

 <!--添加權(quán)限-->
 <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

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