[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);
}

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