iphone - 从 UITextField 添加一个对象到 NSMutableArray

Question

使用此代码，我收到此错误:

'* -[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它时，在弹出警报 View 之前我就崩溃了。有什么想法吗？

Answer 1

如果你尝试添加一个 nil 对象，NSArray 中将会引发异常。首先检查情况:

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

编辑:

此外，从您的代码中，您需要实现 UIAlertViewDelegate 协议(protocol)并尝试将对象添加到那里的数组中。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 iVar，当不再需要它们时，您需要释放它们。您还应该检查委托(delegate)方法中按下了哪个按钮。 HTH 戴夫