ios - iOS 中的持久图像存储

Question

我使用此方法来存储图像，据我了解，此方法会持久存储数据。问题是当我重新启动模拟器时，所有图像都消失了/无法加载。无论如何，这是代码:

- (NSString *)saveImage:(NSMutableString*)account{
        NSString *dir=[NSString stringWithFormat:@"http://example.com"];
        NSURL *url=[NSURL URLWithString:dir];
        NSData *imageData = UIImagePNGRepresentation([UIImage imageWithData:[NSData dataWithContentsOfURL:url]]);
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentDirectory = [paths objectAtIndex:0];
        NSString *imageName = [NSString stringWithFormat:@"%@%@", account,@"Banner.png"];
        NSString *imagePath = [documentDirectory stringByAppendingFormat:imageName];
        NSLog((@"pre writing to file"));
        NSError *writeError = nil;
        if(![imageData writeToFile:imagePath options:NSDataWritingAtomic error:&writeError]){
            NSLog(@"%@: Error saving image: %@",[self class], [writeError localizedDescription]);
        }
        else{
            NSLog(@"the cachedImagePath is %@", imagePath);
            return imagePath;
        }
        return NULL;
    }

这是用于加载图像的方法:

[UIImage imageWithContentsOfFile:bannerPath]

bannerPath是保存在NSUserDefaults中的保存方法返回的imagePath。

我做错了什么吗？我该如何解决？谢谢。

编辑:我用下面的方法检查文件是否存在:

[[NSFileManager defaultManager] fileExistsAtPath:bannerPath];

我返回 false。

Answer 1

NSString *imagePath = [documentDirectory stringByAppendingFormat:imageName]; 

我认为应该是

NSString *imagePath =    [documentDirectory stringByAppendingPathComponent:imageName];