Add a new Objective-C class called TextureManager derived from AssetsDictionary within the Assets group.

Add an instance method that will register a texture using its filename and return the correct value, which is the following:

-(SPTexture *) registerTexture:(NSString *)filename;

Switch to TextureManager.m and implement the method with the following content:

-(SPTexture *) registerTexture:(NSString *)filename
{
    if ([_dict objectForKey:filename] == nil) {
    return (SPTexture *) [self registerAsset:filename withContent:[SPTexture textureWithContentsOfFile:filename]];
  } else {
    return (SPTexture *) [self registerAsset:filename withContent:nil];
  }
}

Switch to the Game.m file, and replace the AssetsDictionary.h import with the TextureManager.h file in the import section.

In the init method, replace the AssetsDictionary test we did earlier in the chapter with the following lines:

TextureManager...