iOS:只调用一次方法

Question

嗨,我想知道如何在应用程序生命中只调用一次方法...我的应用程序应该从服务器下载一些文件,我只需要做一次; 我的意思是每次安装只需要一次

这是我的方法

//Download some images from server and save it into directory 

- (void) downloadCovers {

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    [self saveFile:@"mag1" ofType:@"png" fromURL:@"http://myweb.com/mag1.png" inDirectory:documentsDirectory];

}

并且此方法将图像设置为UIButton BG:

  - (void)buttonsBGImage {

       UIImage * bgMag1 = [self loadImage:@"mag1" ofType:@"png" inDirectory:[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]];

        [mag1 setBackgroundImage:bgMag1 forState:UIControlStateNormal];
         NSLog(@"BG IS SET");

    }

Answer 1

为什么不测试文件是否存在于本地存储中!

//Download some images from server and save it into directory 

- (void) downloadCovers {

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *pathToImg = [NSString stringWithFormat:@"%@/mag1.png",documentsDirectory];
    BOOL isExist = [[NSFileManager defaultManager]fileExistsAtPath:pathToImg];
    if (!isExist) {
        [self saveFile:@"mag1" ofType:@"png" fromURL:@"http://myweb.com/mag1.png" inDirectory:documentsDirectory];
    }

}