private Activity activity;
  private Scroller scroller;
  //上次ACTION_MOVE时的X坐标
  private int last_X;
  //屏幕宽度
  private int width;
  //可滑动的最小X坐标，小于该坐标的滑动不处理
  private int min_X;
  // 页面边缘的阴影图
  private Drawable left_shodow;
  //页面边缘阴影的宽度默认值
  private static final int SHADOW_WIDTH = 16;
  // 页面边缘阴影的宽度
  private int shadow_width;
  // Activity finish标识符
  private boolean isFinish;

 private void initView(Activity activity) {
    this.activity = activity;
    scroller = new Scroller(activity);
    left_shodow = getResources().getDrawable(R.drawable.left_shadow);
    int density = (int) activity.getResources().getDisplayMetrics().density;
    shadow_width = SHADOW_WIDTH * density;
    // 这里你一定要设置成透明背景,不然会影响你看到底层布局
    setBackgroundColor(Color.argb(0, 0, 0, 0));
  }

  public void bindActivity(Activity activity) {
    ViewGroup decorView = (ViewGroup) activity.getWindow().getDecorView();
    View child = decorView.getChildAt(0);
    decorView.removeView(child);
    addView(child);
    decorView.addView(this);

public abstract class SWBackActivity extends Activity {

  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    SWBackLayout layout = new SWBackLayout(this);
    layout.bindActivity(this);
  }

  protected abstract void afterInject();

  protected abstract void afterInitView();

}

  public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:
        last_X = (int) event.getX();
        width = getWidth();
        min_X = width / 10;
        break;
      case MotionEvent.ACTION_MOVE:
        int rightMovedX = last_X - (int) event.getX();
        if (getScrollX() + rightMovedX >= 0) {// 左侧即将滑出屏幕
          scrollTo(0, 0);
        } else if ((int) event.getX() > min_X) {// 手指处于屏幕边缘时不处理滑动
          scrollBy(rightMovedX, 0);
        }
        last_X = (int) event.getX();
        break;
      case MotionEvent.ACTION_UP:
        if (-getScrollX() < width / 3) {
          scrollBack();
          isFinish = false;
        } else {
          scrollClose();
          isFinish = true;
        }
        break;
    }
    return true;
  }

  private void scrollBack() {
    int startX = getScrollX();
    int dx = -getScrollX();
    scroller.startScroll(startX, 0, dx, 0, 300);
    invalidate();
  }

  private void scrollClose() {
    int startX = getScrollX();
    int dx = -getScrollX() - width;
    scroller.startScroll(startX, 0, dx, 0, 300);
    invalidate();
  }

  public void computeScroll() {
    if (scroller.computeScrollOffset()) {
      scrollTo(scroller.getCurrX(), 0);
      postInvalidate();
    } else if (isFinish) {
      activity.finish();
    }
    super.computeScroll();
  }

  protected void dispatchDraw(Canvas canvas) {
    super.dispatchDraw(canvas);
    drawShadow(canvas);
  }

  private void drawShadow(Canvas canvas) {
    // 保存画布当前的状态
    canvas.save();
    // 设置drawable的大小范围
    left_shodow.setBounds(0, 0, shadow_width, getHeight());
    // 让画布平移一定距离
    canvas.translate(-shadow_width, 0);
    // 绘制Drawable
    left_shodow.draw(canvas);
    // 恢复画布的状态
    canvas.restore();
  }