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;
}

//
//  MainViewController.m
//  UIByCodeDemo0602_ImageView
//
//  Created by yao_yu on 14-6-3.
//  Copyright (c) 2014年 yao_yu. All rights reserved.
//

#import "MainViewController.h"

@interface MainViewController ()

@property(nonatomic, strong)UILabel *header;
@property(nonatomic, strong)UIImageView *imageView;
@property(nonatomic, strong)UIImage *imagedata;

@end

@implementation MainViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.imagedata = nil;
    
    //创建标题标签
    self.header = [[UILabel alloc] init];
    self.header.text = @"示意图";
    self.header.textAlignment = NSTextAlignmentCenter;
    [self.view addSubview: self.header];
    [self.header setTranslatesAutoresizingMaskIntoConstraints: NO];
    
    //创建图片视图
    self.imageView = [[UIImageView alloc] init];
    [self.imageView setBackgroundColor: [UIColor blueColor]];
    [self.imageView setImage: [UIImage imageWithContentsOfFile:@"/Users/yao_yu/Documents/aaa/3002302_.png"]];
    self.imageView.layer.cornerRadius = 10;
    [self.view addSubview:self.imageView];
    [self.imageView setTranslatesAutoresizingMaskIntoConstraints: NO];
    
    //创建前一张按钮
    UIButton *prevButton = [[UIButton alloc] init];
    prevButton.frame = CGRectMake(0, 20, 300, 20);
    [prevButton setBackgroundColor:[UIColor redColor]];
    [prevButton setTitle:@"前一张" forState:UIControlStateNormal];
    [prevButton addTarget:self action:@selector(onShowPrevImage:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview: prevButton];
    [prevButton setTranslatesAutoresizingMaskIntoConstraints: NO];
    
    //创建后一张按钮
    UIButton *nextButton = [[UIButton alloc] init];
    nextButton.frame = CGRectMake(0, 20, 300, 20);
    [nextButton setBackgroundColor:[UIColor redColor]];
    [nextButton setTitle:@"后一张" forState:UIControlStateNormal];
    [nextButton addTarget:self action:@selector(onShowNextImage:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview: nextButton];
    [nextButton setTranslatesAutoresizingMaskIntoConstraints: NO];
    
    //约束
    NSMutableArray *contraits = [NSMutableArray array];
    NSDictionary *metrics = [NSDictionary dictionaryWithObjectsAndKeys:@20, @"VDist", @5, @"Padding", nil];
    UILabel *header = self.header;
    UIImageView *imageView = self.imageView;
    NSDictionary *views = NSDictionaryOfVariableBindings(header, imageView, prevButton, nextButton);
    
    [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-Padding-[header]-Padding-|" options:0 metrics:metrics views:views]];
    [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-Padding-[prevButton]-(>=0)-[nextButton(==prevButton)]-Padding-|" options:0 metrics:metrics views:views]];
    
    [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-Padding-[imageView]-Padding-|" options:0 metrics:metrics views:views]];
    [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-VDist-[header]-Padding-[imageView]-(>=VDist)-|" options:0 metrics:metrics views:views]];
    //垂直居中
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:prevButton attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:nextButton attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];
    
    [self.view addConstraints:contraits];
    
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}

-(void)onShowPrevImage:(id)sender
{
    NSURL *URL = [NSURL URLWithString:@"http://img.gtimg.cn/images/hq_parts/hushen/stocks/300230.png"];
    NSURLRequest *request = [NSURLRequest requestWithURL:URL];
    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDataTask *task = [session dataTaskWithRequest:request
                                            completionHandler:
                                  ^(NSData *data, NSURLResponse *response, NSError *error) {
                                      self.imageView.image = nil;
                                      self.imagedata = [UIImage imageWithData:data];
                                      [self performSelectorOnMainThread:@selector(updateMyImage) withObject:nil  waitUntilDone:NO];
                                  }];
    
    [task resume];
    
}

-(void)onShowNextImage:(id)sender
{
    NSURL *URL = [NSURL URLWithString:@"http://img.gtimg.cn/images/hq_parts/hushen/stocks/300023.png"];
    NSURLRequest *request = [NSURLRequest requestWithURL:URL];
    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDataTask *task = [session dataTaskWithRequest:request
                                            completionHandler:
                                  ^(NSData *data, NSURLResponse *response, NSError *error) {
                                      self.imageView.image = nil;
                                      self.imagedata = [UIImage imageWithData:data];
                                      [self performSelectorOnMainThread:@selector(updateMyImage) withObject:nil  waitUntilDone:NO];
                                  }];
    
    [task resume];
}

- (void)updateMyImage
{
    if (!self.imageView.image)
        self.imageView.image = self.imagedata;
    return;
}

@end

iOS: 学习笔记, 使用performSelectorOnMainThread及时刷新UIImageView,布布扣,bubuko.com

iOS: 学习笔记, 使用performSelectorOnMainThread及时刷新UIImageView