从的UITextField

Question

将对象添加到NSMutableArray里有了这个代码，我得到这个错误：

'* -[NSMutableArray insertObject:atIndex:]: attempt to insert nil object at 0'

categories=[[NSMutableArray alloc] init ]; 
UIAlertView* dialog = [[UIAlertView alloc] init]; 
    [dialog setDelegate:self]; 
    [dialog setTitle:@"Category name"]; 
    [dialog setMessage:@" "]; 
    [dialog addButtonWithTitle:@"Cancel"]; 
    [dialog addButtonWithTitle:@"OK"]; 

    nameField = [[UITextField alloc] initWithFrame:CGRectMake(20.0, 45.0, 245.0, 25.0)]; 
    [nameField setBackgroundColor:[UIColor whiteColor]]; 
    [dialog addSubview:nameField]; 

    [dialog show]; 
    [dialog release]; 

    [categories addObject:[nameField text]]; 

    [nameField release]; 
    [categoryTable reloadData]; 

当我在模拟器中运行这个，我得到一个崩溃前的警报视图甚至弹出。有任何想法吗？

Answer 1

如果您尝试添加零对象，则会在NSArray中引发异常。检查条件第一：

if ([nameField text]) [categories addObject:[nameField text]]; 

编辑：

从您的代码

此外，您还需要实现UIAlertViewDelegate协议，并尝试将对象添加到您的阵中还有。例如：

- (void) showDialog { 
    UIAlertView* dialog = [[UIAlertView alloc] init]; 
    [dialog setDelegate:self]; 
    [dialog setTitle:@"Category name"]; 
    [dialog setMessage:@" "]; 
    [dialog addButtonWithTitle:@"Cancel"]; 
    [dialog addButtonWithTitle:@"OK"]; 

    nameField = [[UITextField alloc] initWithFrame:CGRectMake(20.0, 45.0, 245.0, 25.0)]; 
    [nameField setBackgroundColor:[UIColor whiteColor]]; 
    [dialog addSubview:nameField]; 

    [dialog show]; 
    [dialog release]; 
} 


- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex { 

    if ([nameField text]) [categories addObject:[nameField text]]; 
    [categoryTable reloadData]; 

} 

假设nameField和categories是iVars，您将需要在不再需要时释放它们。您还应该检查委托方法中按下了哪个按钮。 HTH戴夫