Android侧边滑动关闭Activity的示例代码

class SlideBackView extends View {

    private Paint mBgPaint, mShadowPaint;
    private RectF mBgRectF, mShadowRectF;
    private float mRatio;
    private float mShadowSize;

    public SlideBackView(Context context) {
      super(context);
      mBgPaint = new Paint();
      mBgPaint.setAntiAlias(true);
      mBgPaint.setColor(0xff000000);
      mShadowPaint = new Paint();
      mShadowPaint.setAntiAlias(true);
      mShadowPaint.setStyle(Paint.Style.FILL);
      mShadowSize = dp2px(15);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
      mBgRectF = new RectF();
      mBgRectF.top = 0;
      mBgRectF.left = 0;
      mBgRectF.bottom = MeasureSpec.getSize(heightMeasureSpec);

      mShadowRectF = new RectF();
      mShadowRectF.top = 0;
      mShadowRectF.bottom = MeasureSpec.getSize(heightMeasureSpec);
    }

    @Override
    protected void onDraw(Canvas canvas) {
      super.onDraw(canvas);
      int width = getMeasuredWidth();
      float right = mRatio * width;
      mBgRectF.right = right;
      mBgPaint.setAlpha((int) (128 * (1 - mRatio)));
      canvas.drawRect(mBgRectF, mBgPaint);
      mShadowRectF.left = right - mShadowSize;
      mShadowRectF.right = right;
      mShadowPaint.setShader(new LinearGradient(mShadowRectF.left, 0, mShadowRectF.right, 0, 0x00000000, 0x26000000, Shader.TileMode.CLAMP));
      canvas.drawRect(mShadowRectF, mShadowPaint);
    }

    public void setDistance(float ratio) {
      mRatio = ratio;
      invalidate();
    }

    private float dp2px(float dpValue) {
      float density = getResources().getDisplayMetrics().density;
      return dpValue * density + 0.5F;
    }
  }

public class SlideBaseActivity extends AppCompatActivity implements ValueAnimator.AnimatorUpdateListener {

  private boolean isAnimate, isSlide, isHandle;
  private float moveNum;
  private float lastX, lastY;
  private int lastPointerCount;
  private float mAnimatedValue;
  private ValueAnimator mValueAnimator;
  private SlideBackView mSlideBackView;
  private float mTouchSlop;
  private List shieldViews = new ArrayList<>();

  @Override
  protected void onCreate(@Nullable Bundle savedInstanceState) {
    getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
    super.onCreate(savedInstanceState);
    initAnimator();
    initSlideBackView();
    mTouchSlop = ViewConfiguration.get(this).getScaledTouchSlop();
  }

  @Override
  public void onAnimationUpdate(ValueAnimator animation) {
    mAnimatedValue = (float) animation.getAnimatedValue();
    moveView(mAnimatedValue);
  }

  @Override
  public boolean dispatchTouchEvent(MotionEvent event) {
    if (!isAnimate) {
      float x = event.getRawX();
      float y = event.getRawY();
      if (event.getPointerCount() != lastPointerCount) {
        lastPointerCount = event.getPointerCount();
        lastX = x;
        lastY = y;
      }
      float offsetX, offsetY;
      switch (event.getAction()) {
        case MotionEvent.ACTION_MOVE:
          offsetX = x - lastX;
          offsetY = y - lastY;
          if (!isHandle) {
            float absX = Math.abs(offsetX);
            float absY = Math.abs(offsetY);
            if (absX > mTouchSlop) {
              if (absX * 0.5f > absY) {
                isSlide = true;
                checkSlide((int) x, (int) y);
              } else {
                isSlide = false;
              }
              isHandle = true;
            }
          } else if (isSlide) {
            moveNum += offsetX;
            if (moveNum <0) {
              moveNum = 0;
            }
            moveView(moveNum);
            lastX = event.getX();
          }
          break;
        case MotionEvent.ACTION_UP:
          if (isHandle) {
            isSlide = false;
            isHandle = false;
            isAnimate = true;
            int width = getWindow().getDecorView().getMeasuredWidth();
            if (moveNum