与performSelector相关

Question

我是iPhone应用程序的新手。我希望在每2秒按下一个按钮时显示一条消息，表明我正在使用此代码。

这个代码只工作一次。这意味着只调用一次。你能帮我解决这个问题吗？

-(IBAction)fortunecookieAction:(id)sender
{
    [self performSelector:@selector(showfortune) withObject:nil afterDelay:2.0];
}

-(void)showfortune
{
    int number=arc4random()%5;
    switch (number) {
        case 0:
            fortunelabel.text=@"A holiday takes you back to the summer of '69";
            break;
        case 1:
            fortunelabel.text=@"A meal turns erotic muffin";
            break;
        case 2:
            fortunelabel.text=@"A massage brings";
            break;
        case 3:
            fortunelabel.text=@"A letter in the pa special delivery";
            break;
        case 4:
            fortunelabel.text=@"A spillage tuoo";
            break;

        default:
            break;  
    }   
}

Answer 1

如果希望每隔2秒调用一次函数，请使用NSTimer。

您将需要scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:来创建计划的计时器

Answer 2

您最好的选择可能是使用NSTimer。您可以很容易地将一个设置为每两秒调用一次操作方法：

在接口(MyViewController.h)中，声明一个NSTimer属性：

@interface MyViewController : UIViewController

@property (nonatomic, retain) NSTimer *myTimer;

@end

然后在你的实现中：

@synthesize myTimer;

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSTimer *newTimer = [NSTimer scheduledTimerWithTimeInterval:2.0f target:self selector:@selector(repeatingTimerFired:) userInfo:nil repeats:YES];
    self.myTimer = newTimer;
    [newTimer release];
}

- (void)viewDidUnload
{
    [super viewDidUnload];

    if ([myTimer isValid]) {
        [myTimer invalidate];
    }    
}

- (void)dealloc
{
    [myTimer release], myTimer = nil;

    [super dealloc];
}

- (void)repeatingTimerFired:(NSTimer *)sender
{
    int number=arc4random()%5;
    switch (number) {
        case 0:
            fortunelabel.text=@"A holiday takes you back to the summer of '69";
            break;
        case 1:
            fortunelabel.text=@"A meal turns erotic muffin";
            break;
        case 2:
            fortunelabel.text=@"A massage brings d";
            break;
        case 3:
            fortunelabel.text=@"A letter in the pa special delivery";
            break;
        case 4:
            fortunelabel.text=@"A spillage tuoo";
            break;

        default:
            break;
}

如果您希望此计时器在用户按下按钮后开始显示消息，只需将计时器创建移动到按钮操作方法中即可。