MagnifierView.h#import 
    
     @interface MagnifierView : UIView {//    CGPoint touchPoint;}@property (nonatomic, strong) UIView *viewToMagnify;@property (nonatomic, assign) CGPoint touchPoint;- (void)drawRect:(CGRect)rect;@endMagnifierView.m#import "MagnifierView.h"@implementation MagnifierView- (void)setTouchPoint:(CGPoint)pt {    _touchPoint = pt;    self.center = CGPointMake(pt.x, pt.y-50);//跟随touchmove 不断得到中心点}- (void)drawRect:(CGRect)rect {    //绘制放大镜效果部分    CGContextRef context = UIGraphicsGetCurrentContext();//获取的是当前view的图形上下文    CGContextTranslateCTM(context,1*(self.frame.size.width*0.5),1*(self.frame.size.height*0.5 + 50));//重新设置坐标系原点    CGContextScaleCTM(context, 1.5, 1.5);//通过调用CGContextScaleCTM函数来指定x, y缩放因子 这里我们是扩大1.5倍    CGContextTranslateCTM(context,-1*(_touchPoint.x),-1*(_touchPoint.y));    [self.viewToMagnify.layer renderInContext:context];//直接在一个 Core Graphics 上下文中绘制放大后的图像，实现放大镜效果}@end///MagnifierView的使用#import "ViewController.h"#import "MagnifierView.h"@interface ViewController () {    MagnifierView *loop;}@property (nonatomic, strong) NSTimer *touchTimer;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.}- (void)touchesBegan:(NSSet
     
       *)touches withEvent:(UIEvent *)event {    //计时器，手指点中0.5秒后启动放大镜效果    self.touchTimer = [NSTimer scheduledTimerWithTimeInterval:0.5                                                       target:self                                                     selector:@selector(addLoop)                                                     userInfo:nil                                                      repeats:NO];    if(loop == nil){        loop = [[MagnifierView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];        loop.viewToMagnify = self.view;        loop.layer.borderColor = [UIColor grayColor].CGColor;        loop.layer.borderWidth = 2;        loop.layer.cornerRadius = 50;        loop.layer.masksToBounds = YES;    }    UITouch *touch = [touches anyObject];    loop.touchPoint = [touch locationInView:self.view];    [loop setNeedsDisplay];    [self.view addSubview:loop];}- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {    //将手指移动信息传出给 handleAction    [self handleAction:touches];}- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {    //手指抬起，将loop（放大镜）去掉    [self.touchTimer invalidate];    self.touchTimer = nil;    [loop removeFromSuperview];    loop = nil;}- (void)addLoop {    [loop bringSubviewToFront:self.view];//让放大镜显示在最上层}- (void)handleAction:(id)timerObj {    NSSet *touches = timerObj;    UITouch *touch = [touches anyObject];    loop.touchPoint = [touch locationInView:self.view];//将本身的touch信息传递给放大镜，设置放大镜的中心点    [loop setNeedsDisplay];//    loop drawRect:<#(CGRect)#>}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end