iOS可以从磁盘写入或读取图像数据

我正在尝试使用以下方法加载图像

我首先检查磁盘上是否已经有图像，如果有，我将从磁盘上获取图像数据并加载它，否则我将从服务器获取图像并写入磁盘，以便第二次需要图像时，我不必访问服务器

if (!imageData && [self connected]) {
    // This needs to be done in on a background thread!
    imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:[serverURL stringByAppendingPathComponent: pathSuffix]]];

    if (imageData) {
        [[NSFileManager defaultManager] createDirectoryAtPath:[path stringByDeletingLastPathComponent] withIntermediateDirectories:YES attributes:nil error:nil];
        [imageData writeToFile:path atomically:YES];
    }

    NSLog(@"server");
}

问题是它似乎没有从磁盘写入或读取。每次我想第二次加载映像时，它仍然会从服务器和

NSLog（@“disk”）读取它们从不被调用

如果有人知道的话，我不知道我做错了什么

-(UIImage *)imageWith:(NSString *)imageName isPreview:(BOOL)preview
{
     //imageName is something like "56.jpg"

     NSString *mainOrPreview = @"Preview";
     if (!preview) {
         mainOrPreview = @"Main";
     }

     NSString *pathSuffix = [[@"Images" stringByAppendingPathComponent:mainOrPreview] stringByAppendingPathComponent:imageName];
     NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:pathSuffix];
     NSData *imageData = [NSData dataWithContentsOfFile:path];

     if (imageData) {
         NSLog(@"disk");
     }

     if (!imageData && [self connected]) {

          imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:[serverURL stringByAppendingPathComponent: pathSuffix]]];

         if (imageData) {

             [imageData writeToFile:path atomically:YES];
         }

         NSLog(@"server");
     }

      return [UIImage imageWithData:imageData];
}

问题是目录不存在于
文档之外。因此，写入文件的尝试失败。最好使用具有
NSError
参数的file方法，以便检查结果

您只需要更新实际从服务器写入映像的代码

if (!imageData && [self connected]) {
    // This needs to be done in on a background thread!
    imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:[serverURL stringByAppendingPathComponent: pathSuffix]]];

    if (imageData) {
        [[NSFileManager defaultManager] createDirectoryAtPath:[path stringByDeletingLastPathComponent] withIntermediateDirectories:YES attributes:nil error:nil];
        [imageData writeToFile:path atomically:YES];
    }

    NSLog(@"server");
}

天啊！你真是个天才！你刚刚救了我。非常感谢你。