iPhone 使用唯一键加载和保存多个 UIImage？

Question

我知道有一些解决方案可以在 iPhone 上保存和加载图像。然而，没有一个对我很有用。

例如，下面的链接有一个很棒的代码块，它可以让您使用唯一的键加载和保存 UIImage，但我无法弄清楚如何在使用此代码加载图像时判断该键下的图像是否已存在或不是。

http://www.Friendlydeveloper.com/2010/02/using-nsfilemanager-to-save-an-image-to-or-loadremove-an-image-from-documents-directory-coding/

//saving an image
- (void)saveImage:(UIImage*)image:(NSString*)imageName {
     NSData *imageData = UIImagePNGRepresentation(image); //convert image into .png format.
     NSFileManager *fileManager = [NSFileManager defaultManager];//create instance of NSFileManager
     NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); //create an array and store result of our search for the documents directory in it
     NSString *documentsDirectory = [paths objectAtIndex:0]; //create NSString object, that holds our exact path to the documents directory
     NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.png", imageName]]; //add our image to the path
     [fileManager createFileAtPath:fullPath contents:imageData attributes:nil]; //finally save the path (image)
     NSLog(@"image saved");
}

//removing an image
- (void)removeImage:(NSString*)fileName {
     NSFileManager *fileManager = [NSFileManager defaultManager];
     NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
     NSString *documentsDirectory = [paths objectAtIndex:0];
     NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.png", fileName]];
     [fileManager removeItemAtPath: fullPath error:NULL];
     NSLog(@"image removed");
}

//loading an image
- (UIImage*)loadImage:(NSString*)imageName {
     NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
     NSString *documentsDirectory = [paths objectAtIndex:0];
     NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.png", imageName]];
     return [UIImage imageWithContentsOfFile:fullPath];
}

如果您能帮我解决这个问题，我将不胜感激。我需要保存多个图像，并根据给定的密钥是否已存在来加载它们。

Answer 1

如果你想获取具有唯一密钥的图像，请尝试使用 UUID。这将始终为您提供具有唯一密钥的图像。例如，这里是使用 UUID 的示例。

- (NSString *)pathForImageFileWithPrefix:(NSString *)Prefix
{
    CFUUIDRef   uuid;
    CFStringRef uuidStr;
    uuid = CFUUIDCreate(NULL);
    uuidStr = CFUUIDCreateString(NULL, uuid);
    NSData *imageData = UIImageJPEGRepresentation(chosenImage, 1.0);
    NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);   
    NSString* documentsDirectory = [paths objectAtIndex:0]; 
    result = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@_%@.png",Prefix, uuidStr]];
    [imageData writeToFile:result atomically:NO];
    CFRelease(uuidStr);
    CFRelease(uuid);
    return result;
}

Answer 2

如果我回答正确，您想知道具有给定图像名称的文件是否已经存在？然后你可以使用

bool fileExists = [NSFileManager defaultManager] fileExistsAtPath:filePath];