Objective c 什么'；这个简单的代码（目标c）有什么错？

我想下载一些网页，但这个示例代码似乎不起作用。 它打印“开始下载”，然后退出，为什么不执行委托方法？ 示例代码中有什么错误？ 谢谢

main.m
#进口
#导入“Test.h”
int main（int argc，const char*argv[]
{
@自动释放池{
Test*Test=[[Test alloc]init]；
[测试下载数据]；
}
[NSThread sleepForTimeInterval:21.0f]；
返回0；
}
测试h
#进口
@接口测试：NSObject
@属性（保留）NSMutableData*接收数据；
@财产（保留）NSURLConnection*连接；
-（void）下载数据；
@结束
Test.m
#导入“Test.h”
@实施测试
-（void）下载数据
{
NSURLRequest*theRequest=
[NSURLRequest requestWithURL:[NSURL URLWithString:@]http://www.sf.net/"]                                  
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60.0]；
_receivedData=[NSMutableData数据，容量：0]；
[NSURLConnection sendSynchronousRequest:请求
回复：无
错误：无]；
NSLog（@“开始下载”）；
如果（！\u连接）{
_接收数据=零；
//通知用户连接失败。
}
}
在这里输入代码
#布拉格标记-
#pragma标记NSURLConnectionDataDelegateenter代码在此处输入方法
-（void）连接：（NSURLConnection*）连接DidReceiverResponse：（NSURResponse*）响应
{
NSLog（@“1”）；
[_receivedDatasetLength:0]；
}
-（void）连接：（NSURLConnection*）连接didReceiveData:（NSData*）数据
{
NSLog（@“2”）；
[_receiveddataappenddata:data]；
}
-（无效）连接：（NSURLConnection*）连接
didFailWithError:（n错误*）错误
{
NSLog（@“3”）；
_连接=零；
_接收数据=零；
//通知用户
NSLog（@“连接失败！错误-%@%”），
[错误本地化描述]，
[[error userInfo]objectForKey:nsurErrorFailingUrlStringErrorKey]）；
}
-（无效）连接IDFinishLoading:（NSURLConnection*）连接
{
NSLog（@“4”）；
NSLog（@“成功！接收到%lu字节的数据”，（无符号长）[[u receivedData length]）；
_连接=零；
_接收数据=零；
}
-（void）ConnectionIDFinishDownloading:（NSURLConnection*）连接目的地URL:（NSURL*）目的地URL
{
NSLog（@“5”）；
}
@结束

同步或异步有两种方法：

在同步模式下，未调用任何委托，且右行为

在异步模式下，您需要使用–initWithRequest:delegate:

---

简而言之，同样的问题是：您的程序需要一个运行循环。您正在使用一个同步请求。不会调用您的委托方法。将请求的结果分配给nsdata对象

nsdata*data=[NSURLConnection sendSynchronousRequest….]或使用异步请求并设置委托！谢谢，我更改了[NSThread sleepForTimeInterval:21.0f]；至[[NSRunLoop main runloop]rununteldate:[NSDate dateWithTimeIntervalSinceNow:50.0]]；和[NSURLConnection sendSynchronousRequest:theRequest returningResponse:nil error:nil]；to _theConnection=[[NSURLConnection alloc]initWithRequest:theRequest委托：self]；再次运行它，它打印begindownload15只有两个方法被调用，数据仍然为null。
main.m

#import <Foundation/Foundation.h>
#import "Test.h"

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        Test * test = [[Test alloc]init];
        [test downloadData];

    }
    [NSThread sleepForTimeInterval:21.0f];

    return 0;
}

Test.h


#import <Foundation/Foundation.h>

@interface Test : NSObject <NSURLConnectionDelegate,NSURLConnectionDataDelegate,NSURLConnectionDownloadDelegate>
@property (retain) NSMutableData * receivedData;
@property (retain) NSURLConnection * theConnection;
- (void) downloadData;
@end

Test.m

#import "Test.h"

@implementation Test
- (void) downloadData
{
    NSURLRequest *theRequest=
      [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.sf.net/"]                                  
                       cachePolicy:NSURLRequestUseProtocolCachePolicy
                   timeoutInterval:60.0];

    _receivedData = [NSMutableData dataWithCapacity: 0];



    [NSURLConnection sendSynchronousRequest:theRequest
                          returningResponse:nil
                                      error:nil];
    NSLog(@"begin download");

    if (!_theConnection) {

        _receivedData = nil;

        // Inform the user that the connection failed.

    }
}

enter code here

#pragma mark -
#pragma mark NSURLConnectionDataDelegateenter code here methods

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response

{
    NSLog(@"1");
    [_receivedData setLength:0];

}

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

{
    NSLog(@"2");
    [_receivedData appendData:data];

}
- (void)connection:(NSURLConnection *)connection

  didFailWithError:(NSError *)error

{
    NSLog(@"3");
    _theConnection = nil;

    _receivedData = nil;



    // inform the user

    NSLog(@"Connection failed! Error - %@ %@",

          [error localizedDescription],

          [[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);

}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection

{


    NSLog(@"4");
    NSLog(@"Succeeded! Received %lu bytes of data",(unsigned long)[_receivedData length]);



    _theConnection = nil;

    _receivedData = nil;

}

-(void) connectionDidFinishDownloading:(NSURLConnection *)connection destinationURL:(NSURL *)destinationURL
{
    NSLog(@"5");
}
@end

_receivedData = [NSURLConnection sendSynchronousRequest:theRequest
                          returningResponse:nil
                                      error:nil];
    NSLog(@"begin download");

    if (!_theConnection) {

        _receivedData = nil;

        // Inform the user that the connection failed.

    }

[NSURLConnection alloc] initWithRequest:delegate:theRequest
                          delegate:self];

NSLog(@"begin download");