ios - NSString concat在设备上不起作用

我有一个小挑战。我正在使用以下代码来连接一个NSString。在控制台上，输出正常，在设备上不起作用。我似乎无法弄清楚我所缺少的。

- (void)loadContent {
    getHTML = @"leap";
    NSLog(@"getHTML start: %@", getHTML);
    int showLeap = selectedLeap +1;
    NSString *leapString = [NSString stringWithFormat:@"%d", showLeap];

    if (showLeap<10) {
        getHTML = [getHTML stringByAppendingString:@"0"];
    }

    getHTML = [getHTML stringByAppendingString:leapString];
    getHTML = [getHTML stringByAppendingString:selectedMenu];
    NSLog(@"getHTML complete: %@", getHTML);

在模拟器上，输出为:

2015-06-03 12:11:57.619 iOS_TWW_EVOLUTION[917:582733] getHTML start: leap
2015-06-03 12:11:57.621 iOS_TWW_EVOLUTION[917:582733] getHTML complete: leap01_summary

在设备上，输出为:

2015-06-03 12:15:40.341 iOS_TWW_EVOLUTION[917:582733] getHTML start: leap
2015-06-03 12:15:40.346 iOS_TWW_EVOLUTION[917:582733] getHTML complete: getHTML complete:

最佳答案

我找到了解决方案。 [NSString stringByAppendingString ...]方法不断在设备上返回nil有点奇怪。这是我使用[NSString stringWithFormat ...]方法的解决方案；

int showLeap = selectedLeap +1;
NSString *first = @"leap";
NSString *second = @""; if (showLeap<10) { second=@"0";}
NSString *third = [NSString stringWithFormat:@"%d", showLeap];
NSString *fourth = selectedMenu;
NSString *getHTML = [NSString stringWithFormat: @"%@%@%@%@", first, second, third, fourth];
NSLog(@"getHTML complete: %@", getHTML);