ios 利用UIScrollView实现图片缩放

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前言：我们希望做出的效果是，实现图片的分页滑动，且每张图片都可以双击或用手指捏合来缩放大小。上一篇讲解UIGestureRecognizer的中，我们介绍的UIPinchGestureRecognizer也可以实现用手指捏合来缩放大小这个功能，这里介绍另外一种方法，直接使用UIScrollView自带的功能实现同样的效果。

实现的大体思路：要实现图片的分页滑动，那么肯定是一个大的ScrollView，而每一张图片都可以放大缩小，那么每张图片imageView必定也在一个scrollView上。

在讲解图片缩放的具体实现之前，我们先来区分几个概念：contentSize、contentOffset 、frame

举个例子：一个ScrollView的frame是（0,0,320,480），contentSize是（960,480）

contentSize 代表scrollview中的全部内容区域，

frame代表scrollview在屏幕中显示的区域，

contentOffset 是scrollview当前显示区域顶点相对于frame顶点的偏移量，如当前显示的是第二幅图，那么它的contentOffset.x就是320；

1、取得屏幕宽高

#define MRScreenWidth CGRectGetWidth([UIScreen mainScreen].applicationFrame)

[[UIScreenmainScreen]bounds].size.width 区别？

2、直接上代码吧

#import "MyZoomViewController.h"
#define MRScreenWidth CGRectGetWidth([UIScreen mainScreen].applicationFrame)
#define MRScreenHeight CGRectGetHeight([UIScreen mainScreen].applicationFrame)@interface MyZoomViewController ()@end@implementation MyZoomViewController
@synthesize srcollView = _srcollView;
@synthesize imageView = _imageView;- (void)viewDidLoad
{
[super viewDidLoad];
_srcollView = [[UIScrollView alloc]init];
_srcollView.delegate = self; _srcollView.userInteractionEnabled = YES;
_srcollView.showsHorizontalScrollIndicator = YES;//是否显示侧边的滚动栏
_srcollView.showsVerticalScrollIndicator = NO;
_srcollView.scrollsToTop = NO;
_srcollView.scrollEnabled = YES;
_srcollView.frame = CGRectMake(0, 0, MRScreenWidth, MRScreenHeight); UIImage *img = [UIImage imageNamed:@"image1.png"];
_imageView = [[UIImageView alloc]initWithImage:img];
//设置这个_imageView能被缩放的最大尺寸，这句话很重要，一定不能少,如果没有这句话，图片不能缩放
_imageView.frame = CGRectMake(0, 0, MRScreenWidth * 2.5, MRScreenHeight * 2.5); [self.view addSubview:_srcollView];
[_srcollView addSubview:_imageView];
[_imageView release];
[_srcollView release]; // Add gesture,double tap zoom imageView.
UITapGestureRecognizer *doubleTapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self
action:@selector(handleDoubleTap:)];
[doubleTapGesture setNumberOfTapsRequired:2];
[_srcollView addGestureRecognizer:doubleTapGesture];
[doubleTapGesture release];// float minimumScale = _srcollView.frame.size.width / _imageView.frame.size.width;//最小缩放倍数
// [_srcollView setMinimumZoomScale:minimumScale];
// [_srcollView setZoomScale:0.5f]; [_srcollView setMinimumZoomScale:0.25f];
[_srcollView setMaximumZoomScale:3.0f];
[_srcollView setZoomScale:0.5f animated:NO];}- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
}
#pragma mark - Zoom methods- (void)handleDoubleTap:(UIGestureRecognizer *)gesture
{
NSLog(@"handleDoubleTap");
float newScale = _srcollView.zoomScale * 1.5;//zoomScale这个值决定了contents当前扩展的比例
CGRect zoomRect = [self zoomRectForScale:newScale withCenter:[gesture locationInView:gesture.view]];
[_srcollView zoomToRect:zoomRect animated:YES];
}- (CGRect)zoomRectForScale:(float)scale withCenter:(CGPoint)center
{
CGRect zoomRect;
zoomRect.size.height = _srcollView.frame.size.height / scale;
NSLog(@"zoomRect.size.height is %f",zoomRect.size.height);
NSLog(@"self.frame.size.height is %f",_srcollView.frame.size.height);
zoomRect.size.width = _srcollView.frame.size.width / scale;
zoomRect.origin.x = center.x - (zoomRect.size.width / 2.0);
zoomRect.origin.y = center.y - (zoomRect.size.height / 2.0);
return zoomRect;
}#pragma mark - UIScrollViewDelegate- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
return _imageView;
}
//当滑动结束时
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale
{
//把当前的缩放比例设进ZoomScale，以便下次缩放时实在现有的比例的基础上
NSLog(@"scale is %f",scale);
[_srcollView setZoomScale:scale animated:NO];
}#pragma mark - View cycle
- (void)dealloc
{
[super dealloc];
}@end