[绍棠] 通过捏合手势缩放图片

{

    UIImage* srcImage;

    CGFloat currentScale;

}

- (void)setupUI {

    self.coverImage = [[UIImageView alloc] initWithFrame:CGRectZero];

    [self.view addSubview:self.coverImage];

    [self.coverImage mas_makeConstraints:^(MASConstraintMaker *make) {

        make.left.right.equalTo(self.coverImage.superview);

        make.top.equalTo(self.navView.mas_bottom).offset(0);

        make.height.equalTo(@((ScreenWidth*9/16)));

    }];

    self.coverImage.contentMode = UIViewContentModeCenter;

    self.coverImage.backgroundColor = [UIColor grayColor];

    self.coverImage.layer.masksToBounds = YES;

    [self.coverImage setUserInteractionEnabled:YES];

    [self.coverImage setMultipleTouchEnabled:YES];

    // 捏合手势

    UIPinchGestureRecognizer *pinchGestureRecognizer = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchView:)];

    [self.coverImage addGestureRecognizer:pinchGestureRecognizer];

}

#pragma mark - 手势处理

// 处理缩放手势

- (void) pinchView:(UIPinchGestureRecognizer *)pinchGestureRecognizer

{

    CGFloat scale = pinchGestureRecognizer.scale;

    // 如果捏合手势刚刚开始

    if (pinchGestureRecognizer.state == UIGestureRecognizerStateBegan)

    {       // 计算当前缩放比

        currentScale = self.coverImage.image.size.width / srcImage.size.width;

    }

    // 根据手势处理器的缩放比例计算图片缩放后的目标大小

    CGSize targetSize = CGSizeMake(srcImage.size.width * scale * currentScale,

                                   srcImage.size.height * scale * currentScale);

    // 对图片进行缩放

    self.coverImage.image = [srcImage scaleToSize:targetSize];

}

注:scaleToSize:是对图片进行缩放的方法, 是UIImage类的扩展

内部实现

- (UIImage *)scaleToSize:(CGSize)size {

    UIGraphicsBeginImageContext(size);

    [self drawInRect:CGRectMake(0,0, size.width, size.height)];

    UIImage * scaledImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return scaledImage;

}