效果如下：

呱呱卡開(kāi)獎(jiǎng)前

呱呱卡開(kāi)獎(jiǎng)后

實(shí)現(xiàn)思路

網(wǎng)上有使用Xfermode來(lái)實(shí)現(xiàn)刮刮卡，這里提供另一種思路簡(jiǎn)潔的實(shí)現(xiàn)

一張呱呱卡有三層，最底層我用一個(gè)TextView控件顯示中獎(jiǎng)內(nèi)容，中間層是刮完之后的顯示圖樣，最上面一層是刮刮卡的封面。手指刮除封面的過(guò)程就是把刮刮卡最上面一層裁剪的過(guò)程。

涉及的知識(shí)點(diǎn)

1. canvas.clipPath(),Path類，Region.Op類
2. onDraw方法和onTouchEvent方法的配合

核心代碼如下：

public class LotteryView extends View {

public static final int STROKE_WIDTH = 15;

private float mEventX;
private float mEventY;

/**
 * 呱呱卡封面 畫筆
 */
private Paint mOverlayPaint;
private RectF mRectBorder;
/**
 * 呱呱卡邊緣 畫筆
 */
private Paint mStrokePaint;
private RectF mRectFill;

private Path mClipPath;


public LotteryView(Context context) {
    this(context,null,0);
}

public LotteryView(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
}

public LotteryView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init();
}


private void init() {
    Bitmap lotteryOverlay = BitmapFactory.decodeResource(getResources(), R.drawable.icon_lottery_overlay);
    mOverlayPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mOverlayPaint.setShader(new BitmapShader(lotteryOverlay, Shader.TileMode.REPEAT, Shader.TileMode.REPEAT));

    mStrokePaint = new Paint();
    mStrokePaint.setAntiAlias(true);
    mStrokePaint.setStyle(Paint.Style.STROKE);
    mStrokePaint.setColor(Color.BLACK);
    mStrokePaint.setStrokeWidth(STROKE_WIDTH);

    mClipPath = new Path();
}

@Override
protected void onDraw(Canvas canvas) {
    if (mRectBorder == null) {
        mRectBorder = new RectF(0, 0, getWidth(), getHeight());
    }
    if (mRectFill == null) {
        mRectFill = new RectF(0, 0, getWidth(), getHeight());
    }

    canvas.drawRoundRect(mRectBorder, 10, 10, mStrokePaint);

    if (mEventX != 0 || mEventY != 0) {
        mClipPath.addCircle(mEventX, mEventY, 50, Path.Direction.CW);
        canvas.clipPath(mClipPath, Region.Op.DIFFERENCE);
    }
    canvas.drawRect(mRectFill, mOverlayPaint);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    int action = event.getAction();
    switch (action) {
        case MotionEvent.ACTION_MOVE:
            mEventX = event.getX();
            mEventY = event.getY();
            invalidate();
            break;
    }
    return true;
}

}

布局里的使用

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="120dp"
    >

    <TextView
        android:id="@+id/tv_lottery_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_centerInParent="true"
        android:gravity="center"
        android:textColor="@android:color/white"
        android:textSize="20sp"
        android:background="@android:color/darker_gray"
        android:text="恭喜您，榮獲2016年年度最佳程序員"
        />
    <com.sugary.roundimageview.LotteryView
        android:layout_width="match_parent"
        android:layout_height="120dp"
        />
</RelativeLayout>

小結(jié)

1. 刮刮卡的中獎(jiǎng)內(nèi)容是放在TextView控件，作為最底層顯示。
2. 如果項(xiàng)目里需要有刮卡完成后回調(diào)，可以計(jì)算刮除的面積與刮刮卡總面積的比例，超過(guò)一定值，即認(rèn)為呱卡完成。
3. 后續(xù)的優(yōu)化方向可以是，把底層的TextView放到LotteryView自定義控件里