UIImage 在下载时损坏

Posted 2023-02-23

【中文标题】UIImage 在下载时损坏

【英文标题】：UIImage gets corrupted while Downloading

【发布时间】：2013-09-12 10:27:42

【问题描述】：

我开发了 ios 应用程序，我在其中从服务器下载图像并将其保存在我的 Document 目录中。

但我面临的问题是，有时我的图像在下载时会损坏，即使服务器响应成功。

这是我的代码 sn-p，

urlFile 是服务器上 UIImage 的路径，例如：www.abcd.com/images/pqr.jpg

我用来在我的 DocDirectory 中保存图像名称的文件名。

- (void)downloadFile:(NSString *)urlFile withName:(NSString *)fileName 

    NSString *trimmedString = [urlFile stringByTrimmingCharactersInSet:
                               [NSCharacterSet whitespaceAndNewlineCharacterSet]];

    NSLog(@"trimmedString=%@",trimmedString);
    if ([trimmedString length]>0)
    
        HTTPEaterResponse *response = [HTTPEater get:[NSString stringWithFormat:@"%@",trimmedString]];

    if ([response isSuccessful])
          
           NSLog(@"isSuccessful");
            [self saveImage:[[UIImage alloc] initWithData:[response body]] withName:fileName];
         else 
            NSLog(@"Url response failed %@", [response description]);
        
    




    - (void)saveImage:(UIImage *)image withName:(NSString *)name
    
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];

        NSData *data = UIImagePNGRepresentation(image);
        NSLog(@"image =%@",image);

        NSFileManager *fileManager = [NSFileManager defaultManager];
        NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:name];
        [fileManager createFileAtPath:fullPath contents:data attributes:nil];

    

当我看到我的日志时，它显示：

trimmedString= www.abcd.com/images/pqr.jpg 成功了 图像=null

提前致谢。

【参考方案1】：

我使用以下代码，它适用于我。

NSData *thumbImageData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:ImageURL]];
[thumbImageData writeToFile:cachedThumbnailFileName atomically:YES];
UIImage * image =  [UIImage imageWithContentsOfFile:cachedThumbnailFileName];
imageView.image = image;

希望对您有所帮助。 :)

【参考方案2】：

要将图像保存到目录使用：

NSString  *pngPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Test.jpg"];
[UIImagePNGRepresentation(selectedImage) writeToFile:pngPath atomically:YES];
NSError *error;
NSFileManager *fileMgr = [NSFileManager defaultManager];  
NSString *documentsDirectory = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];

【讨论】：

selectedImage 是什么？

【参考方案3】：

您是否记录了回复[response body]？

只需尝试将该响应转换为NSData，然后另存为图像。 使用Base64Encoding 类，您可以将响应转换为base64Data

NSData *imageData = [NSString base64DataFromString:[response body]];
[self saveImage:[[UIImage alloc] initWithData:imageData] withName:fileName];

【讨论】：

显示错误：不知道选择器base64DataFromString:的类方法

使用这个答案***.com/a/800976/1160493 其中包含base64DataFromString 方法。

【参考方案4】：

我建议你使用 SDWebimage 类SDWebimage 下载.. 我认为它对你很有帮助，即使我一直更喜欢 SDWebimage 库。 这是一些事情。

An UIImageView category adding web image and cache management to the Cocoa Touch framework
An asynchronous image downloader
An asynchronous memory + disk image caching with automatic cache expiration handling
Animated GIF support
WebP format support
A background image decompression
A guarantee that the same URL won't be downloaded several times
A guarantee that bogus URLs won't be retried again and again
A guarantee that main thread will never be blocked
Performances!
Use GCD and ARC

【参考方案5】：

你可以使用“NSURLRequest”和“NSURLConnection” 例如，如果你得到图像 URL，那么，

    NSURL* aURL = [NSURL URLWithString:trimmedString];//get the url of string
    NSURLRequest *aReq = [NSURLRequest requestWithURL:aURL];
    NSURLConnection *aConnection = [NSURLConnection connectionWithRequest:aReq delegate:self]; //get a connection to url , since it confirms to delegate u need to implement delegate methods 
    if(aConnection == nil) //if it is nil then cancel and close the request
     
       aConnection = nil;  
      [aConnection cancel];
    


   // after this implement this delegate methods
  - (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)received_data
  
      if(image_data == nil)    //if data is not initialised initialise it
      
          image_data = [[NSMutableData alloc]init];
      

      [self.image_data appendData:received_data];//append the received data

  
  //this method is called after successful download of the image
  - (void)connectionDidFinishLoading:(NSURLConnection *)connection;
 
    // UIImage* sampleImage = [UIImage imageWithData:self.image_data];
    // self.image = sampleImage; //convert the data to image 
    //since u hav complete downloaded date in "self.image_data"

    NSString *imagePath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:@"/myImage.png"];//set the name of the image and path may it saving in application directory check it out  
    [self.image_data writeToFile:imagePath atomically:YES]; //saving the data with name
 

希望对你有帮助:)

【讨论】：

如何为下载的图片命名？？

也可以看到这个答案***.com/questions/6238139/…