自定义刮刮卡

效果图

效果图

知识点（自定义TextView）,重新方法

• onTouchEvent
• onDraw

1.自定义变量

   private Bitmap mDownBitmap, mUpBitmap;//图片
    private Paint mPaint; //画笔
    private Canvas mCanvas; //画布
    private Path mPath; //用于绘制复杂的图形轮廓，比如折线，圆弧以及各种复杂图案

2.初始化方法init()：

private void init() {
        mPaint = new Paint();
        mPaint.setAlpha(0);//画笔透明度为0
        //使用DST_IN模式将路径绘制到前面覆盖的图层上
        mPaint.setXfermode(
                new PorterDuffXfermode(PorterDuff.Mode.DST_IN));

        mPaint.setStyle(Paint.Style.STROKE);
        //笔触和连接处更加圆滑
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeWidth(50);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPath = new Path();
        mDownBitmap = BitmapFactory.decodeResource(getResources(),
                R.drawable.ic_launcher);
        mUpBitmap = Bitmap.createBitmap(mDownBitmap.getWidth(),
                mDownBitmap.getHeight(), Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mUpBitmap);
        mCanvas.drawColor(Color.GRAY);
    }

其中PorterDuffXfermode有16种混合模式的效果

效果图

3.重新onTouchEvent方法：

public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mPath.reset();//清除path设置的所有属性
                mPath.moveTo(event.getX(), event.getY());//将起始轮廓点移至x，y坐标点，默认情况为0,0点
                break;
            case MotionEvent.ACTION_MOVE:
                mPath.lineTo(event.getX(), event.getY()); //用于从当前轮廓点绘制一条线段到x，y点
                break;
        }
        mCanvas.drawPath(mPath, mPaint); //重新绘制Path
        invalidate(); //刷新
        return true;
    }

4.重新onDraw方法：

 protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //绘制图片
        canvas.drawBitmap(mDownBitmap, 0, 0, null);
        canvas.drawBitmap(mUpBitmap, 0, 0, null);
    }

完整版代码：

public class GuaGuaCard extends View {
    private Bitmap mDownBitmap, mUpBitmap;//图片
    private Paint mPaint; //画笔
    private Canvas mCanvas; //画布
    private Path mPath; //用于绘制复杂的图形轮廓，比如折线，圆弧以及各种复杂图案

    public GuaGuaCard(Context context) {
        super(context);
        init();
    }

    public GuaGuaCard(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public GuaGuaCard(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }


    private void init() {
        mPaint = new Paint();
        mPaint.setAlpha(0);//画笔透明度为0
        //使用DST_IN模式将路径绘制到前面覆盖的图层上
        mPaint.setXfermode(
                new PorterDuffXfermode(PorterDuff.Mode.DST_IN));

        mPaint.setStyle(Paint.Style.STROKE);
        //笔触和连接处更加圆滑
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeWidth(50);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPath = new Path();
        mDownBitmap = BitmapFactory.decodeResource(getResources(),
                R.drawable.ic_launcher);
        mUpBitmap = Bitmap.createBitmap(mDownBitmap.getWidth(),
                mDownBitmap.getHeight(), Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mUpBitmap);
        mCanvas.drawColor(Color.GRAY);
    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mPath.reset();//清除path设置的所有属性
                mPath.moveTo(event.getX(), event.getY());//将起始轮廓点移至x，y坐标点，默认情况为0,0点
                break;
            case MotionEvent.ACTION_MOVE:
                mPath.lineTo(event.getX(), event.getY()); //用于从当前轮廓点绘制一条线段到x，y点
                break;
        }
        mCanvas.drawPath(mPath, mPaint); //重新绘制Path
        invalidate(); //刷新
        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //绘制图片
        canvas.drawBitmap(mDownBitmap, 0, 0, null);
        canvas.drawBitmap(mUpBitmap, 0, 0, null);
    }
}

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