如何使 PerformSelector:withObject:afterDelay 工作？

Question

代码如下：

-(void)setProjectID:(NSString *)newProject {
    [self willChangeValueForKey:@"projectID"];
    [projectID release];
    projectID = [newProject copy];
    [self didChangeValueForKey:@"projectID"];

    // Since we have an ID, now we need to load it
    NSInvocation *returnInvocation = [NSInvocation invocationWithMethodSignature:
                                      [Detail instanceMethodSignatureForSelector:@selector(configureView:)]];
    [returnInvocation setTarget:self];
    [returnInvocation performSelector:@selector(displayAlert) withObject:nil afterDelay:0.5];
    [returnInvocation setSelector:@selector(configureView:)];
    [returnInvocation retainArguments];

    fetch = [[WBWDocumentFetcher alloc] init];
    [fetch retrieveDocument:[NSURL wb_URLForTabType:PROJECT_DETAILS inProject:projectID] returnBy:returnInvocation];
}

-(void)displayAlert
{
    UIAlertView * alert = [[UIAlertView alloc]
                           initWithTitle:@"Connection Error" 
                           message:@"Error loading Data."
                           delegate:self cancelButtonTitle:@"OK" 
                           otherButtonTitles:nil];
    [alert show];
    [alert release];
}

应用程序崩溃并显示 NSInvalidArguementException。 -[NSInspiration displayAlert]：无法识别的选择器发送到实例 0x5842320 请帮忙！！！

Answer 1

我想代码应该像：

NSInvocation *returnInvocation = [NSInvocation invocationWithMethodSignature:
                                  [Detail instanceMethodSignatureForSelector:@selector(displayAlert)]];

[returnInvocation setTarget:self];
[returnInvocation setSelector:@selector(displayAlert)];
[returnInvocation invoke];

或简单地：

[self performSelector:@selector(displayAlert) withObject:nil afterDelay:0.5];

Answer 2

不要使用 withObject，只需使用 PerformSelector:afterDelay:

另外，您应该在 self 上调用此函数，而不是 returnInitation >

Answer 3

[self performSelector:@selector(displayAlert) withObject: message afterDelay:0.5];

试试这个..

Answer 4

- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay 在调用它的对象上执行。

因此，如果您在 returnInitation 上调用它，您将收到无法识别的选择器错误，因为 NSInitation 没有 displayAlert 方法。

使用

[self PerformSelector:@selector(displayAlert) withObject:nil afterDelay:0.5];

因为 self 有该方法。