在iOS中, 界面刷新在主线程中进行, 这导致NSURLSession远程下载图片使用UIImageView直接设置Image并不能及时刷新界面.
下面的代码演示了如何使用 performSelectorOnMainThread: withObject: waitUntilDone: 方法来及时刷新图片
1. 创建iOS空应用程序(Empty Application).
2. 加入一个控制器类. 在YYAppDelegate.m中修改
#import "MainViewController.h" @implementation YYAppDelegate - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; // Override point for customization after application launch. self.window.backgroundColor = [UIColor whiteColor]; self.window.rootViewController = [[MainViewController alloc] initWithNibName:nil bundle:nil]; [self.window makeKeyAndVisible]; return YES; }
3. 修改MainViewController.m文件
1 // 2 // MainViewController.m 3 // UIByCodeDemo0602_ImageView 4 // 5 // Created by yao_yu on 14-6-3. 6 // Copyright (c) 2014年 yao_yu. All rights reserved. 7 // 8 9 #import "MainViewController.h" 10 11 @interface MainViewController () 12 13 @property(nonatomic, strong)UILabel *header; 14 @property(nonatomic, strong)UIImageView *imageView; 15 @property(nonatomic, strong)UIImage *imagedata; 16 17 @end 18 19 @implementation MainViewController 20 21 - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil 22 { 23 self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; 24 if (self) { 25 // Custom initialization 26 } 27 return self; 28 } 29 30 - (void)viewDidLoad 31 { 32 [super viewDidLoad]; 33 self.imagedata = nil; 34 35 //创建标题标签 36 self.header = [[UILabel alloc] init]; 37 self.header.text = @"示意图"; 38 self.header.textAlignment = NSTextAlignmentCenter; 39 [self.view addSubview: self.header]; 40 [self.header setTranslatesAutoresizingMaskIntoConstraints: NO]; 41 42 //创建图片视图 43 self.imageView = [[UIImageView alloc] init]; 44 [self.imageView setBackgroundColor: [UIColor blueColor]]; 45 [self.imageView setImage: [UIImage imageWithContentsOfFile:@"/Users/yao_yu/Documents/aaa/3002302_.png"]]; 46 self.imageView.layer.cornerRadius = 10; 47 [self.view addSubview:self.imageView]; 48 [self.imageView setTranslatesAutoresizingMaskIntoConstraints: NO]; 49 50 //创建前一张按钮 51 UIButton *prevButton = [[UIButton alloc] init]; 52 prevButton.frame = CGRectMake(0, 20, 300, 20); 53 [prevButton setBackgroundColor:[UIColor redColor]]; 54 [prevButton setTitle:@"前一张" forState:UIControlStateNormal]; 55 [prevButton addTarget:self action:@selector(onShowPrevImage:) forControlEvents:UIControlEventTouchUpInside]; 56 [self.view addSubview: prevButton]; 57 [prevButton setTranslatesAutoresizingMaskIntoConstraints: NO]; 58 59 //创建后一张按钮 60 UIButton *nextButton = [[UIButton alloc] init]; 61 nextButton.frame = CGRectMake(0, 20, 300, 20); 62 [nextButton setBackgroundColor:[UIColor redColor]]; 63 [nextButton setTitle:@"后一张" forState:UIControlStateNormal]; 64 [nextButton addTarget:self action:@selector(onShowNextImage:) forControlEvents:UIControlEventTouchUpInside]; 65 [self.view addSubview: nextButton]; 66 [nextButton setTranslatesAutoresizingMaskIntoConstraints: NO]; 67 68 //约束 69 NSMutableArray *contraits = [NSMutableArray array]; 70 NSDictionary *metrics = [NSDictionary dictionaryWithObjectsAndKeys:@20, @"VDist", @5, @"Padding", nil]; 71 UILabel *header = self.header; 72 UIImageView *imageView = self.imageView; 73 NSDictionary *views = NSDictionaryOfVariableBindings(header, imageView, prevButton, nextButton); 74 75 [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-Padding-[header]-Padding-|" options:0 metrics:metrics views:views]]; 76 [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-Padding-[prevButton]-(>=0)-[nextButton(==prevButton)]-Padding-|" options:0 metrics:metrics views:views]]; 77 78 [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-Padding-[imageView]-Padding-|" options:0 metrics:metrics views:views]]; 79 [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-VDist-[header]-Padding-[imageView]-(>=VDist)-|" options:0 metrics:metrics views:views]]; 80 //垂直居中 81 [self.view addConstraint:[NSLayoutConstraint constraintWithItem:prevButton attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]]; 82 [self.view addConstraint:[NSLayoutConstraint constraintWithItem:nextButton attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]]; 83 84 [self.view addConstraints:contraits]; 85 86 } 87 88 - (void)didReceiveMemoryWarning 89 { 90 [super didReceiveMemoryWarning]; 91 } 92 93 -(void)onShowPrevImage:(id)sender 94 { 95 NSURL *URL = [NSURL URLWithString:@"http://img.gtimg.cn/images/hq_parts/hushen/stocks/300230.png"]; 96 NSURLRequest *request = [NSURLRequest requestWithURL:URL]; 97 NSURLSession *session = [NSURLSession sharedSession]; 98 NSURLSessionDataTask *task = [session dataTaskWithRequest:request 99 completionHandler: 100 ^(NSData *data, NSURLResponse *response, NSError *error) { 101 self.imageView.image = nil; 102 self.imagedata = [UIImage imageWithData:data]; 103 [self performSelectorOnMainThread:@selector(updateMyImage) withObject:nil waitUntilDone:NO]; 104 }]; 105 106 [task resume]; 107 108 } 109 110 -(void)onShowNextImage:(id)sender 111 { 112 NSURL *URL = [NSURL URLWithString:@"http://img.gtimg.cn/images/hq_parts/hushen/stocks/300023.png"]; 113 NSURLRequest *request = [NSURLRequest requestWithURL:URL]; 114 NSURLSession *session = [NSURLSession sharedSession]; 115 NSURLSessionDataTask *task = [session dataTaskWithRequest:request 116 completionHandler: 117 ^(NSData *data, NSURLResponse *response, NSError *error) { 118 self.imageView.image = nil; 119 self.imagedata = [UIImage imageWithData:data]; 120 [self performSelectorOnMainThread:@selector(updateMyImage) withObject:nil waitUntilDone:NO]; 121 }]; 122 123 [task resume]; 124 } 125 126 - (void)updateMyImage 127 { 128 if (!self.imageView.image) 129 self.imageView.image = self.imagedata; 130 return; 131 } 132 133 @end
4. 运行