如何在 Objective-c 中的应用程序的资源文件夹中保存文件

我正在为 iPhone 开发一个 Objective-C 应用程序。我的问题是我的应用程序必须保存从网址获取的图像。我认为该文件夹是只读的。这是我保存图像的代码：

-(void)banner:(NSString *)path{
    NSData * imageData = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString: path]];
    UIImage *image = [UIImage imageWithData: imageData];
    NSString* resourcePath = [[NSBundle mainBundle] resourcePath];
    NSString* pathEnd =  [resourcePath stringByAppendingFormat:@"/banner.png"];
    NSData *data1 = [NSData dataWithData:UIImagePNGRepresentation(image)];
    NSError *writeError = nil;
    [data1 writeToFile:pathEnd options:NSDataWritingAtomic error:&writeError];
}

但是当我检索图像时，它不在该文件夹中。我能做些什么？

你不能，应用程序包是只读的。您应该将所有数据保存在文档或缓存目录中。

-(void)banner:(NSString *)path{
    NSData * imageData = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString: path]];
    UIImage *image = [UIImage imageWithData: imageData];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES); 
    NSString *filePath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"banner.png"];

    NSData *data1 = [NSData dataWithData:UIImagePNGRepresentation(image)];
    NSError *writeError = nil;

   [data1 writeToFile:filePath options:NSDataWritingAtomic error:&writeError];

   if (writeError) {
      NSLog(@"Error writing file: %@", writeError);
   }
}

是否有任何理由先将数据转换为图像，然后再转换回图像NSData又反对？

如果没有，你可以这样做：

-(void)banner:(NSString *)path{
   NSData * imageData = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString: path]];
   NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);         NSString *filePath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"banner.png"];       
   NSError *writeError = nil;
   [imageData writeToFile:filePath options:NSDataWritingAtomic error:&writeError];

   if (writeError) {
      NSLog(@"Error writing file: %@", writeError);
   }
}