1.截取制定范围（非长图）

- (UIImage *)screenShotWithSize(CGSize *)size {
    UIImage* image = nil;
    /*
     *UIGraphicsBeginImageContextWithOptions有三个参数
     *size    bitmap上下文的大小，就是生成图片的size
     *opaque  是否不透明，当指定为YES的时候图片的质量会比较好
     *scale   缩放比例，指定为0.0表示使用手机主屏幕的缩放比例
     */
    UIGraphicsBeginImageContextWithOptions(size, YES, 0.0);
    //此处我截取的是TableView的header.
    [self.tableHeaderView.layer renderInContext: UIGraphicsGetCurrentContext()];
    image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
    if (image != nil) {
        return image;
    }else {
        return nil;
    }
}

2.截取长图，如TableView，CollectionView

- (UIImage *)screenShot {
    UIImage* image = nil;
    UIGraphicsBeginImageContextWithOptions(self.collectionView.contentSize, YES, 0.0);

    //保存collectionView当前的偏移量
    CGPoint savedContentOffset = self.collectionView.contentOffset;
    CGRect saveFrame = self.collectionView.frame;

    //将collectionView的偏移量设置为(0,0)
    self.collectionView.contentOffset = CGPointZero;
    self.collectionView.frame = CGRectMake(0, 0, self.collectionView.contentSize.width, self.collectionView.contentSize.height);

    //在当前上下文中渲染出collectionView
    [self.collectionView.layer renderInContext: UIGraphicsGetCurrentContext()];
    //截取当前上下文生成Image
    image = UIGraphicsGetImageFromCurrentImageContext();

    //恢复collectionView的偏移量
    self.collectionView.contentOffset = savedContentOffset;
    self.collectionView.frame = saveFrame;

    UIGraphicsEndImageContext();

    if (image != nil) {
        return image;
    }else {
        return nil;
    }
}

3.图片拼接

将两张图片拼接在一起，第二张图片拼接在第一张图的下面。

/*masterImage  主图片，生成的图片的宽度为masterImage的宽度
 *slaveImage   从图片，拼接在masterImage的下面
 *／
- (UIImage *)addSlaveImage:(UIImage *)slaveImage toMasterImage:(UIImage *)masterImage {
    CGSize size;
    size.width = masterImage.size.width;
    size.height = masterImage.size.height + slaveImage.size.height;
    
    UIGraphicsBeginImageContextWithOptions(size, YES, 0.0);
    
    //Draw masterImage
    [masterImage drawInRect:CGRectMake(0, 0, masterImage.size.width, masterImage.size.height)];
    
    //Draw slaveImage
    [slaveImage drawInRect:CGRectMake(0, masterImage.size.height, masterImage.size.width, slaveImage.size.height)];
    
    UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    return resultImage;
}