ios - 在 tableView 的文档目录中存储和检索图像？

Question

我正在尝试将来自 web 服务的图像存储在文档目录中。对于存储的图像，我想从 TableView 中的文档目录加载它。 可以从 url 访问图像，例如:- http://Address/App/User/Image/Puegeot_E7

从 web 服务中获取是成功的，但是从文档目录中我一直得到空图像。似乎无法找到这里的问题。

- (void)saveImage:(UIImage*)image withName:(NSString *)imageName
{
    if (image != nil)
    {
        NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];
        NSString* path = [documentsDirectory stringByAppendingPathComponent:imageName];

        NSLog(@"Saving path %@",path); // Saving path /Users/computername/Library/Developer/CoreSimulator/Devices/7277F3D3-298C-451A-8607-8070A08650C7/data/Containers/Data/Application/D3AF4DD9-A4CD-42C8-A8EB-0F15C271EE61/Documents/CabImage/Puegeot_E7

        NSData* data = UIImagePNGRepresentation(image);
        [data writeToFile:path atomically:YES];
    }
}

- (UIImage *)getImageFromURL:(NSString *)fileURL
{
   NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                     NSUserDomainMask, YES);
   NSString *documentsDirectory = [paths objectAtIndex:0];
   NSString *path = [documentsDirectory stringByAppendingPathComponent:fileURL];
   NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:path]];
   NSLog(@"data %@",data); //This returns (null)
   UIImage *result = [UIImage imageWithData:data];
   return result;
}

在 tableView 中，这就是我尝试从文档目录加载的方式。

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
   //default initialisation stuff
   NSDictionary *obj = [responseArray objectAtIndex:indexPath.row];
   cell.imgVW.image = [UIImage imageNamed:@"default-car.png"];
   NSString *imgPath = obj[@"cabimage"];
   NSLog(@"imgPath : %@",imgPath); // imgPath : Image/Puegeot_E7 
   UIImage *imgFromDisk = [self getImageFromURL:imgPath];
   NSLog(@"imgFromDisk - %@",imgFromDisk); -> (null)
   if (imgFromDisk) 
   {
       cell.imgVW.image = imgFromDisk;
   }
   else
   {
       //download
       NSURL *imageURL = [NSURL URLWithString:[NSString stringWithFormat:@"%@User/%@",BASE_URL,imgPath]];

       self.task = [self.session downloadTaskWithURL:imageURL 
                   completionHandler:^(NSURL *location,NSURLResponse *response,NSError *error)
       {
            NSData *img_data = [NSData dataWithContentsOfURL:imageURL];
            if (img_data) 
            {
                 UIImage *img = [UIImage imageWithData:img_data];
                 dispatch_async(dispatch_get_main_queue(), ^{
                    ListCell *cell = (id)[tableView cellForRowAtIndexPath:indexPath];
                    cell.imgVW.image = img;                                 
                    [self saveImage:img withName:imgPath];

                });
            }
       }];
       [self.task resume];
   }
}

Answer 1

从您在日志中看到的内容来看，问题似乎很明显:

NSLog(@"imgPath : %@",imgPath); // imgPath : Image/Puegeot_E7

该路径不在文档目录中。

为了对此进行更严格的控制，让 save 方法返回保存图像的路径:

- (NSString *)saveImage:(UIImage*)image withName:(NSString *)imageName{
    // op code, then:
    return path;
}

测试您是否可以读回图像。 (此代码用于测试，不适用于应用程序)。

UIImage *testImage = [UIImage imageNamed:@"some_test_image"];
NSString *path = [self saveImage:testImage withName:@"test_name"];
UIImage *didItWork = [self getImageFromURL:path];
NSLog(@"did it work? %@", didItWork);

回到真正的应用程序...在模型中写入图像返回的路径之后:

UIImage *downloadedImage = // however you get this
NSString * downloadedImageName = // however you get this
NSDictionary *obj = [responseArray objectAtIndex:indexPath.row];
obj[@"cabbage"] = [self saveImage: downloadedImage withName:downloadedImageName];

现在我们知道您的 cellForRowAtIndexPath 方法将看到保存的路径，并且我们从测试中知道从该路径创建图像将起作用。