NSConnection和RunLoop的关系

#import "ViewController.h"
@interface ViewController () <NSURLConnectionDataDelegate>
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    NSURLConnection *conn = [NSURLConnection connectionWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://120.25.226.186:32812/resources/images/minion_01.png"]] delegate:self];
    // 决定代理方法在哪个队列中执行（在子线程中执行）
        [conn setDelegateQueue:[[NSOperationQueue alloc] init]];
}

#pragma mark - <NSURLConnectionDataDelegate>
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    NSLog(@"didReceiveResponse----%@", [NSThread currentThread]);
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{

    NSLog(@"didReceiveData----%@", [NSThread currentThread]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"connectionDidFinishLoading----%@", [NSThread currentThread]);
}

@end

上面这段程序是在主线程中创建NSURLConnection ，给服务器发送请求，程序可以成功的接受到服务器返回的数据
但是一但将请求放在子线程中发送，就不能接受到服务器返回的数据了。情况如下面代码所示：

- (void)viewDidLoad {
    [super viewDidLoad];
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSURLConnection *conn = [NSURLConnection connectionWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://120.25.226.186:32812/resources/images/minion_01.png"]] delegate:self];
        // 决定代理方法在哪个队列中执行（在子线程中执行）
        [conn setDelegateQueue:[[NSOperationQueue alloc] init]];
    });
}

这是为什么呢，原因如下：

• 因为NSURLConnection跟RunLoop有关系
• NSURLConnection发出请求，等待接收服务器一点一点返回的数据，需要有一个运行循环等待服务器给NSURLConnection数据，也就是说NSURLConnection是在RunLoop中接收服务器返回的数据
• NSURLConnection内部会关联当前线程对应的RunLoop，不断的给当前线程的RunLoop传递消息，RunLoop接收到Source进行处理
• NSURLConnection在子线程发送请求时，子线程的RunLoop默认是不启动的，所以接受不到服务器返回的数据。在主线程中，主线程的RunLoop是默认启动的，所以可以接受服务器返回的数据
• 要想NSURLConnection在子线程发送请求，可以接收到服务器返回的数据，要开启子线程的RunLoop，具体方法如下，有两种方法实现：
  
  • 方法一：

#import "ViewController.h"
@interface ViewController () <NSURLConnectionDataDelegate>
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSURLConnection *conn = [NSURLConnection connectionWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://120.25.226.186:32812/resources/images/minion_01.png"]] delegate:self];
        // 决定代理方法在哪个队列中执行
        [conn setDelegateQueue:[[NSOperationQueue alloc] init]];

        // 启动子线程的runLoop
        [[NSRunLoop currentRunLoop] run];
    });
}

#pragma mark - <NSURLConnectionDataDelegate>
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    NSLog(@"didReceiveResponse----%@", [NSThread currentThread]);
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{

    NSLog(@"didReceiveData----%@", [NSThread currentThread]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"connectionDidFinishLoading----%@", [NSThread currentThread]);
}
@end

• 方法二：

#import "ViewController.h"
@interface ViewController () <NSURLConnectionDataDelegate>
/** runLoop */
@property (nonatomic, assign) CFRunLoopRef runLoop;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSURLConnection *conn = [NSURLConnection connectionWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://120.25.226.186:32812/resources/images/minion_01.png"]] delegate:self];
        // 决定代理方法在哪个队列中执行
        [conn setDelegateQueue:[[NSOperationQueue alloc] init]];

        // 启动子线程的runLoop
        self.runLoop = CFRunLoopGetCurrent();

        // 启动runLoop
        CFRunLoopRun();
    });
}

#pragma mark - <NSURLConnectionDataDelegate>
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    NSLog(@"didReceiveResponse----%@", [NSThread currentThread]);
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{

    NSLog(@"didReceiveData----%@", [NSThread currentThread]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"connectionDidFinishLoading----%@", [NSThread currentThread]);

    // 一般来说RunLoop会自己停止，然是如果RunLoop没有自动停止，我们可以手动停止
    // CFRunLoopStop(self.runLoop);
}
@end