ios UIImageView異步加載網絡圖片2

 //1. NSData dataWithContentsOfURL
//    [self.icon setImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:tempUrl]]];
    
    //2. dispath形式添加到異步處理
//    [self imageDownLoadByUrlASYNC:tempUrl Complete:^(UIImage *image) {
//        [self.icon setImage:image];
//    }];
    //3. 當前我所選用的方式 邊下載邊加載的方式 用的CGImageRef imageWithCGImage
    _request = [[NSURLRequest alloc] initWithURL:tempUrl];
    _conn    = [[NSURLConnection alloc] initWithRequest:_request delegate:self];
    
    _incrementallyImgSource = CGImageSourceCreateIncremental(NULL);
    
    _recieveData = [[NSMutableData alloc] init];
    _isLoadFinished = false;
    
    self.icon.alpha = .5;
    self.lblTitle.alpha = .5;
    [self.lblTitle setText:appName];

第一種方式，是基本上不多有人用的 是最基礎的方式 這種方式有個問題 就是網絡很差的狀況下會卡主線程，致使程序假死

 

第二種方式，請款這段實現代碼

//
//-(void)imageDownLoadByUrlASYNC:(NSURL *)url Complete:(complete)finished
//{
//    //異步並列執行
//    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//        UIImage *image = nil;
//        NSError *error;
//        NSData *responseData = [NSData dataWithContentsOfURL:url options:NSDataReadingMappedIfSafe error:&error];
//        image = [UIImage imageWithData:responseData];
//        //跳回主隊列執行
//        dispatch_async(dispatch_get_main_queue(), ^{
//            //在主隊列中進行ui操做
//            finished(image);
//        });
//        
//    });
//}

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        NSError *error;

        UIImage *image = nil;

        SDWebImageManager *manager = [SDWebImageManager sharedManager];

        BOOL existBool = [manager diskImageExistsForURL:url];//判斷是否有緩存

        if (existBool) {

            image = [[manager imageCache] imageFromDiskCacheForKey:url.absoluteString];

        }else{

            NSData *responseData = [NSData dataWithContentsOfURL:url options:NSDataReadingMappedIfSafe error:&error];

            image = [UIImage imageWithData:responseData];

        }

        //跳回主隊列執行

        dispatch_async(dispatch_get_main_queue(), ^{

            //在主隊列中進行ui操做

            __block CGFloat itemW = mWidth;

            __block CGFloat itemH = 0;

            NSLog(@"%f",image.size.width);

            //根據image的比例來設置高度

            if (image.size.width) {

                itemH = image.size.height / image.size.width * itemW;

                if (itemH >= itemW) {

                    if (itemH >= mHeight-64) {

                        NSLog(@"%f",[UIScreen mainScreen].bounds.size.width);

                        UIScrollView *sv = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 64, itemW, mHeight-64)];

                        sv.contentSize = CGSizeMake(itemW, itemH);

                        sv.showsVerticalScrollIndicator = NO;

                        sv.userInteractionEnabled = YES;

                        [self.view addSubview:sv];

                        imageView.frame = CGRectMake(0, 0, itemW, itemH);

                        imageView.contentMode = UIViewContentModeScaleAspectFit;

                        [sv addSubview:imageView];

                    }else{

                        imageView.frame = CGRectMake(0, 64, itemW, itemH);

                        imageView.contentMode = UIViewContentModeScaleAspectFit;

                        [self.view addSubview:imageView];

                    }

                }else{

                    imageView.frame = CGRectMake(0, 64, itemW, itemH);

                    imageView.contentMode = UIViewContentModeScaleAspectFit;

                    [self.view addSubview:imageView];

                }

            }else{

                imageView.frame = CGRectMake(0, 64, mWidth, mHeight-64);

                imageView.contentMode = UIViewContentModeScaleAspectFit;

                [self.view addSubview:imageView];

            }

            [self.myView stopAnimating];

        });

    });

 

雖然狀況跟第一種實現同樣，可是將執行代碼添加到對應的異步執行中 而後再成功下載以後 獲取到image以後 放到主線程執行回調 設置image

 

 

第三種方式 須要如下代碼 這是我百度到的方式

 

#pragma mark -- NSURLConnectionDataDelegate

-(void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse*)response
{
    _expectedLeght=response.expectedContentLength;
    NSLog(@"expectedLength:%lld",_expectedLeght);
    
    NSString*mimeType=response.MIMEType;
    NSLog(@"MIMETYPE%@",mimeType);
    
    NSArray*arr=[mimeType componentsSeparatedByString:@"/"];
    if(arr.count<1||![[arr objectAtIndex:0] isEqual:@"image"])
    {
        NSLog(@"notaimageurl");
        [connection cancel];
        _conn=nil;
    }
}
-(void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error
{
    NSLog(@"Connection%@error,errorinfo:%@",connection,error);
}
-(void)connectionDidFinishLoading:(NSURLConnection*)connection
{
    NSLog(@"ConnectionLoadingFinished!!!");
    //ifdownloadimagedatanotcomplete,createfinalimage
    if(!_isLoadFinished){
        CGImageSourceUpdateData(_incrementallyImgSource,(CFDataRef)_recieveData,_isLoadFinished);
        CGImageRef imageRef=CGImageSourceCreateImageAtIndex(_incrementallyImgSource,0,NULL);
        UIImage * image=[UIImage imageWithCGImage:imageRef];
        [self.icon setImage:image];
        CGImageRelease(imageRef);
        }
}
-(void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data
{
    [_recieveData appendData:data];
    
    _isLoadFinished=false;if(_expectedLeght==_recieveData.length){
        _isLoadFinished=true;
        }
    
    CGImageSourceUpdateData(_incrementallyImgSource,(CFDataRef)_recieveData,_isLoadFinished);
    CGImageRef imageRef=CGImageSourceCreateImageAtIndex(_incrementallyImgSource,0,NULL);
    UIImage * image=[UIImage imageWithCGImage:imageRef];
    [self.icon setImage:image];
    CGImageRelease(imageRef);
}

這個方法通過我測試了 很是好用 可是不知道會不會有什麼bug 只是剛使用 而且用戶體驗也會相應增長