一、简单说明
线程间通信:在1个进程中,线程往往不是孤立存在的,多个线程之间需要经常进行通信
线程间通信的体现
1个线程传递数据给另1个线程
在1个线程中执行完特定任务后,转到另1个线程继续执行任务
线程间通信常用方法
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait;
- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait;
线程间通信示例 – 图片下载
代码1:
#import "ViewController.h"
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
}
// 手指触摸屏幕时开始下载图片
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
// 后台线程中调用downloadImage 方法下载图片
[self performSelectorInBackground:@selector(downloadImage) withObject:nil];
}
// 下载图片
- (void)downloadImage
{
// 根据URL下载图片
// 将字符串转换成URL
NSURL *url = [NSURL URLWithString:@"https://img-blog.csdn.net/20151124230511915?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"];
// 根据URL下载图片数据
NSData *data = [NSData dataWithContentsOfURL:url]; // 这一句代码会比较耗时
// 将二进制数据转换成图片
UIImage *image = [UIImage imageWithData:data];
// 回到主线程中设置图片更新UI
[self performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:NO];
}
// 设置显示图片
- (void)setImage:(UIImage *)image
{
self.imageView.image = image;
}
@end
代码2:
#import "ViewController.h"
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
}
// 手指触摸屏幕时开始下载图片
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
// 后台线程中调用downloadImage 方法下载图片
[self performSelectorInBackground:@selector(downloadImage) withObject:nil];
}
// 下载图片
- (void)downloadImage
{
// 根据URL下载图片
// 将字符串转换成URL
NSURL *url = [NSURL URLWithString:@"https://img-blog.csdn.net/20151124230511915?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast"];
// 根据URL下载图片数据
NSData *data = [NSData dataWithContentsOfURL:url]; // 这一句代码会比较耗时
// 将二进制数据转换成图片
UIImage *image = [UIImage imageWithData:data];
// 回到主线程中设置图片更新UI
// 第一种方式
// [self performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:NO];
// 第二种方式
// [self.imageView performSelector:@selector(setImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:NO];
// 第三种方式
[self.imageView performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:NO];
}
// 设置显示图片
//- (void)setImage:(UIImage *)image
//{
// self.imageView.image = image;
//}
@end
注意:在iOS9 beta中,苹果将原http协议改成了https协议,使用 TLS1.2 SSL加密请求数据,所以不能直接使用http协议访问网络资源,需要在info.plist 加入key
<key>NSAppTransportSecurity</key>
<dict>
<key>NSAllowsArbitraryLoads</key>
<true/>
</dict>