支持左右渐变

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public class EdgeGradientLayout extends FrameLayout {

  private Paint mPaint;
  //左侧渐变
  private boolean leftGradient;
  //右侧渐变
  private boolean rightGradient;

  private int mWidth;
  private int mHeight;

  private int mDrawSize = 100;

  //渐变颜色
  private int[] mGradientColors = { 0xffffffff, 0x00000000 };
  //渐变位置
  private float[] mGradientPosition = new float[] { 0, 1 };

  public EdgeGradientLayout (Context context) {
    this(context, null);
  }

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

  private void initShader() {
    if (mPaint == null) {
      mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
      mPaint.setStyle(Paint.Style.FILL);
      mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
      mPaint.setShader(new LinearGradient(0, 0, 0, mDrawSize, mGradientColors, mGradientPosition,
          Shader.TileMode.CLAMP));
    }
  }

  @Override
  protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    initShader();
    mWidth = getWidth();
    mHeight = getHeight();
  }

  @Override protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
    int layerSave = canvas.saveLayer(0, 0, getWidth(), getHeight(), null, Canvas.ALL_SAVE_FLAG);
    boolean drawChild = super.drawChild(canvas, child, drawingTime);

    float offset = (mHeight - mWidth) / 2f;
    if (leftGradient) {
      int saveCount = canvas.save();
      canvas.rotate(270, mWidth / 2f, mHeight / 2f);
      canvas.translate(0, offset);
      canvas.drawRect(0 - offset, 0, mWidth + offset, mDrawSize, mPaint);
      canvas.restoreToCount(saveCount);
    }

    if (rightGradient) {
      int saveCount = canvas.save();
      canvas.rotate(90, mWidth / 2f, mHeight / 2f);
      canvas.translate(0, offset);
      canvas.drawRect(0 - offset, 0, mWidth + offset, mDrawSize, mPaint);
      canvas.restoreToCount(saveCount);
    }

    canvas.restoreToCount(layerSave);
    return drawChild;
  }

  public void setLeftGradient(boolean leftGradient) {
    this.leftGradient = leftGradient;
  }

  public void setRightGradient(boolean rightGradient) {
    this.rightGradient = rightGradient;
  }

  public void setDrawSize(int mDrawSize) {
    this.mDrawSize = mDrawSize;
  }
}