iphone下实现图片的缩放和居中显示

这是实现图片缩放和居中显示的Demo:ScaleMoveImageDemo

程序参考自：http://blog.sina.com.cn/s/blog_9c3c519b0100za22.html

要实现图片的缩放和居中，我们需要用到UIScrollView来控制图片的缩放和居中显示(通过设置maximumZoomScale和minimumZoomScale两个属性来规定图片的最大最小比例，接着在scrollViewDidZoom函数中设置图片的居中显示)。

以下是一些重要的做法：

1、新建一个Empty Application工程testMoveScaleImage，记得打上Use Automatic Reference Counting 这个钩。

2、新建一个UIViewController，命名为MoveScaleImage。

在MoveScaleImage.h文件中，加入以下代码

@interface MoveScaleImage : UIViewController<UIScrollViewDelegate>
{
    UIScrollView *myScrollView;
    UIImageView* myImageView;
}

@property(retain,nonatomic)UIScrollView* myScrollView;
@property(retain,nonatomic)UIImageView* myImageView;

@end

在MoveScaleImage.h中，在开头部分加入

@synthesize myScrollView;
@synthesize myImageView;

loadView函数：

-(void)loadView{
    [super loadView];
    self.view.backgroundColor = [UIColor lightGrayColor];
    
    //    UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    UIButton *btn = [[UIButton alloc]initWithFrame:CGRectMake(110, 200, 100, 50)];
    //    [btn setFrame:CGRectMake(110, 200, 100, 40)];
    [btn setBackgroundColor:[UIColor whiteColor]];
    [btn setTitle:@"点击查看图片" forState:UIControlStateNormal];
    [btn.titleLabel setFont:[UIFont systemFontOfSize:13]];
    [btn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [btn addTarget:self action:@selector(clickEvent:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];
}

-(void)clickEvent:(id)sender{
    NSLog(@"***********clickeventad");
    myScrollView = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
    if(self.myScrollView==nil)
    {
        UIScrollView *scrollView=[[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        self.myScrollView=scrollView;
    }
    self.myScrollView.backgroundColor=[UIColor blueColor];
    self.myScrollView.delegate=self;
    self.myScrollView.multipleTouchEnabled=YES; //是否支持多点触控
    self.myScrollView.minimumZoomScale=1.0;  //表示与原图片最小的比例
    self.myScrollView.maximumZoomScale=10.0; //表示与原图片最大的比例
    [self.view addSubview:self.myScrollView];
    
    UIImage *_image = [UIImage imageNamed:@"QQ.png"];
    CGFloat imageView_X = (_image.size.width > self.view.frame.size.width) ? self.view.frame.size.width : _image.size.width;
    CGFloat imageView_Y=(_image.size.height > self.view.frame.size.height) ? self.view.frame.size.height : _image.size.height;
    CGFloat origin;
    //保持图片的比例
    if(_image.size.width > self.view.frame.size.width){
        origin = self.view.frame.size.width/_image.size.width;
        imageView_Y = _image.size.height*origin;
    }
    
    myImageView = [[UIImageView alloc]initWithFrame:CGRectMake((self.view.frame.size.width-imageView_X)/2, (self.view.frame.size.height-imageView_Y)/2, imageView_X, imageView_Y)];
    
    if(self.myImageView==nil)
    {
        UIImageView *imageView=[[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        self.myImageView=imageView;
    }
    
    
    UIImage *originImage=[[UIImage alloc]initWithCGImage:_image.CGImage];
    [myImageView setImage:originImage];
    //    [myImageView setFrame:CGRectMake(0, 0, _image.size.width, _image.size.height)];
    
    [self.myScrollView addSubview:self.myImageView];
    
    //返回按钮
    UIButton *closeBtn = [[UIButton alloc]initWithFrame:CGRectMake(10, 10, 50, 50)];
    [closeBtn setBackgroundColor:[UIColor redColor]];
    [closeBtn setTitle:@"返回" forState:UIControlStateNormal];
    [closeBtn setAlpha:0.5];
    [closeBtn addTarget:self action:@selector(closeEvent:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:closeBtn];
    
}


//按下该按钮将隐藏myImageView和myScrollView
-(void)closeEvent:(id)sender{
    [self.myImageView setHidden:YES];
    [self.myScrollView setHidden:YES];
}

//实现图片在缩放过程中居中
- (void)scrollViewDidZoom:(UIScrollView *)scrollView
{
    CGFloat offsetX = (scrollView.bounds.size.width > scrollView.contentSize.width)?(scrollView.bounds.size.width - scrollView.contentSize.width)/2 : 0.0;
    CGFloat offsetY = (scrollView.bounds.size.height > scrollView.contentSize.height)?(scrollView.bounds.size.height - scrollView.contentSize.height)/2 : 0.0;
    self.myImageView.center = CGPointMake(scrollView.contentSize.width/2 + offsetX,scrollView.contentSize.height/2 + offsetY);
}


//返回缩放的是哪个ImageView
-(UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView{
    NSLog(@"**************viewForZoomingInScrollView");
    return self.myImageView;
}

以上就是MoveScaleImage的实现部分。

最后记得在AppDelegate.m头部加入:

#import "MoveScaleImage.h"

self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    MoveScaleImage* moveScaleImage=[[MoveScaleImage alloc] init];
    self.window.rootViewController=moveScaleImage; //记得加这行代码，否则会出错
    [self.window addSubview:moveScaleImage.view];
    
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;