[Android实例] 拖动滑块进行图片拼合验证方式的实现

该篇文章从eoeAndroid搬迁过来的，原文地址：[Android实例] 拖动滑块进行图片拼合验证方式的实现

现在网站上有各种各样的验证码验证方式，比如计算大小，输入图片内容等，今天在一家网站上看到这样的一种效果，感觉眼前一亮，验证方式是给出一张缺失一点的图片，然后在旁边有缺失部分的滑块，需要将该滑块拖动到图片缺失的地方补全才能验证成功，看到这种方式，我就想如何在android上去实现这种滑动验证的效果。 
我的思路是，自定义控件，重写onDraw方法

1.根据原图和控件的大小裁剪出对应比例的背景图片，然后在控件中绘制出该背景图片

// 根据原图进行裁剪出适合当前屏幕的背景图
        if (bgBitmap == null) {
            if (bitmap == null) {
                return;
            }
            bgBitmap = Bitmap.createBitmap(getWidth(), getHeight(), Config.ARGB_8888);
            Canvas bgCanvas = new Canvas(bgBitmap);
            Rect bgRect;
            if (bitmap.getWidth() / getWidth() < bitmap.getHeight() / getHeight()) {
                bgRect = new Rect(0, 0, bitmap.getWidth(), bitmap.getWidth() * bitmap.getHeight() / getWidth());
            } else {
                bgRect = new Rect(0, 0, bitmap.getWidth() * bitmap.getHeight() / getHeight(), bitmap.getHeight());
            }
            bgCanvas.drawBitmap(bitmap, bgRect, new Rect(0, 0, getWidth(), getHeight()), paint);
            bitmap.recycle();
            bitmap = null;
        }
        // 绘制背景图
        canvas.drawBitmap(bgBitmap, null, new Rect(0, 0, getWidth(), getHeight()), paint);

2.计算背景图片缺失部分的左上角的位置，以及缺失部分图片所在初始位置的起点，绘制缺失部分的位置并裁剪缺失部分的图片

// 计算验证的点和拖动起点
                if (verifyPoint == null) {
                        int width = getWidth();
                        int height = getHeight();
                        int randomY = (int) (Math.random() * height);
                        int verifyX = width * 3 / 4 - 10;
                        int verifyY = randomY + height / 4 + 10 > height ? height * 3 / 4 - 10 : randomY;
                        verifyPoint = new Point(verifyX, verifyY);
                        startPoint = new Point(10, verifyY);
                }
                paint.setColor(Color.GRAY);
                paint.setStyle(Paint.Style.FILL);
                paint.setAntiAlias(true);
                // 绘制验证的位置
                Rect verifyRect = new Rect(verifyPoint.x, verifyPoint.y, verifyPoint.x + getWidth() / 4,
                                verifyPoint.y + getHeight() / 4);
                canvas.drawRect(verifyRect, paint);
                // 裁剪拖动的图片
                if (verifyBitmap == null) {
                        verifyBitmap = Bitmap.createBitmap(getWidth() / 4, getHeight() / 4, Config.ARGB_8888);
                        Canvas verifyCanvas = new Canvas(verifyBitmap);
                        verifyCanvas.drawBitmap(bgBitmap, verifyRect,
                                        new Rect(0, 0, verifyBitmap.getWidth(), verifyBitmap.getHeight()), paint);
                }

3.绘制裁剪的缺失部分图片

// 拖动图片的绘制
                if (isMoving) {// 拖动中
                        canvas.drawRect(new Rect(movePoint.x - 2, movePoint.y - 2, movePoint.x + getWidth() / 4 + 2,
                                        movePoint.y + getHeight() / 4 + 2), paint);
                        canvas.drawBitmap(verifyBitmap, null,
                                        new Rect(movePoint.x, movePoint.y, movePoint.x + getWidth() / 4, movePoint.y + getHeight() / 4),
                                        paint);
                } else {
                        canvas.drawRect(new Rect(startPoint.x - 2, startPoint.y - 2, startPoint.x + getWidth() / 4 + 2,
                                        startPoint.y + getHeight() / 4 + 2), paint);
                        canvas.drawBitmap(verifyBitmap, null,
                                        new Rect(startPoint.x, startPoint.y, startPoint.x + getWidth() / 4, startPoint.y + getHeight() / 4),
                                        paint);
                }

4.重写onTouchEvent方法

@Override
        public boolean onTouchEvent(MotionEvent event) {
                // TODO Auto-generated method stub
                switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                        if (event.getX() > startPoint.x && event.getX() < startPoint.x + getWidth() / 4
                                        && event.getY() > startPoint.y && event.getY() < startPoint.y + getHeight() / 4) {
                                movePoint = new Point(startPoint);
                                moveX = (int) event.getX();
                                isMoving = true;
                                invalidate();
                                return true;
                        }
                        break;
                case MotionEvent.ACTION_MOVE:
                        if (isMoving) {
                                if (movePoint.x + getWidth() / 4 < getWidth() && movePoint.x > 0) {
                                        invalidate();
                                }
                                movePoint = new Point((int) (movePoint.x + event.getX() - moveX), movePoint.y);
                                moveX = (int) event.getX();
                                return true;
                        }
                        break;
                case MotionEvent.ACTION_UP:
                        if (isMoving) {
                                if (onVerifyListener != null) {
                                        if (Math.abs(movePoint.x - verifyPoint.x) < 10) {
                                                onVerifyListener.success();
                                        } else {
                                                onVerifyListener.fail();
                                        }
                                }
                                isMoving = false;
                                movePoint = null;
                                moveX = 0;
                                invalidate();
                                return true;
                        }
                        break;
                default:
                        break;
                }
                return super.onTouchEvent(event);
        }

下载地址：项目代码