使用ASIHTTPRequest第三方类库,来实现上传下载

使用ASIHTTPRequest第三方类库,来实现上传下载,两个按钮"下载开始"和"暂停"分别绑定方法,使用alloc,init方式创建Request,在"暂停"方法中清除协议方法和取消,未关ARC,已经配置好各项内容,点击"下载开始"按钮可以执行,但一点"暂停"程序就崩,一直说指向了被释放的对象,不知是什么原因,难道不可以Arc和非ARC混用?
求教各位大神.

@interface YLMViewController ()
//{
//    ASIHTTPRequest *_request;
//}

@property (weak, nonatomic) IBOutlet UIProgressView *downloadProgressView;
@property (weak, nonatomic) IBOutlet UIProgressView *uploadProgressView;
@property (nonatomic,retain)ASIHTTPRequest *request;
@end

@implementation YLMViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}
- (NSString *)filePath{
    return [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Download.zip"];

}
- (NSString *)temFilePath{
    return [NSHomeDirectory() stringByAppendingPathComponent:@"tmp/tmp"];
}
- (IBAction)downloadClick:(UIButton *)sender {
    NSURL *url=[NSURL URLWithString:@"http://localhost:8080/MyXMLServer/netBeans.zip"];

   _request =[[ASIHTTPRequest alloc]initWithURL:url];

//     _request=request;
    _request.timeOutSeconds = 30;
    _request.downloadProgressDelegate=self;
    [_request setDownloadDestinationPath:[self filePath]];
    [_request setTemporaryFileDownloadPath:[self temFilePath]];
    [_request setAllowResumeForFileDownloads:YES];
    [_request start];

     NSLog(@"request--------%p",_request);
}
- (IBAction)downloadPause:(UIButton *)sender
{
    NSLog(@"request2--------%@",_request);
    NSLog(@"===========");
    [self.request clearDelegatesAndCancel];
}

ASIHTTPRequest类库使用简介
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