/** *  系統在第一次使用這個類的時候調用(1個類只會調用一次) */+ (void)initialize{    // 設置導航欄主題    UINavigationBar *navBar = [UINavigationBar appearance];    // 設置背景圖片    NSString *bgName = nil;    if (iOS7) { // 至少是iOS 7.0        bgName = @"NavBar64";    } else { // 非iOS7        bgName = @"NavBar";    }    [navBar setBackgroundImage:[UIImage imageNamed:bgName] forBarMetrics:UIBarMetricsDefault];        // 設置標題文字顏色    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];    attrs[NSForegroundColorAttributeName] = [UIColor whiteColor];    attrs[NSFontAttributeName] = [UIFont systemFontOfSize:16];    [navBar setTitleTextAttributes:attrs];        //設置BarButtonItem的主題    UIBarButtonItem *item=[UIBarButtonItem appearance];    //設置文字顏色    NSMutableDictionary *itemAttrs=[NSMutableDictionary dictionary];    itemAttrs[NSFontAttributeName]=[UIFont systemFontOfSize:14];    itemAttrs[NSForegroundColorAttributeName]=[UIColor whiteColor];    [item setTitleTextAttributes:itemAttrs forState:UIControlStateNormal];    if (!iOS7) {        //設置按鈕背景                [item setBackgroundImage:[UIImage imageNamed:@"NavButton"] forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];        [item setBackgroundImage:[UIImage imageNamed:@"NavButtonPRessed"] forState:UIControlStateHighlighted barMetrics:UIBarMetricsDefault];                //設置返回按鈕的背景        [item setBackButtonBackgroundImage:[UIImage imageNamed:@"NavButton"] forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];        [item setBackButtonBackgroundImage:[UIImage imageNamed:@"NavButtonPressed"] forState:UIControlStateHighlighted barMetrics:UIBarMetricsDefault];    }    else{        navBar.tintColor=[UIColor whiteColor];    }   }