验证UITextField输入并显示错误

Question

验证UITextField中的用户输入并显示错误的最佳做法是什么？我尝试在textFieldShouldReturn和textFieldShouldEndEditing内执行检查，并在userever输入无效内容时弹出错误框。

但是，在测试期间，从textFieldShouldEndEditing弹出多次调用。我的简单测试是在TextFieldA中输入无效文本并直接导航到TextFieldB。我观察到3个错误弹出窗口，所有产生的textFieldShouldReturn

Answer 1

这可能是通过展示警报，编辑栏失去焦点，并由此发出另一个textFieldShouldReturn或textFieldShouldEndEditing。

尝试推迟警报，通过将代码，以显示警报到一个单独的方法，和从textFieldShouldEndEditing调用该方法使用[自performSelector：@selector（yourAlertMethod）withObject：无afterDelay：0]

其实，我发现前段时间我有类似的问题。诀窍是确保文本字段在显示警报的持续时间内不再有焦点。

这里是我的解决方案：

// declare this in your interface as part of your ivars: 
UITextField *currTextField; 

// here comes the code to check for bad input and show an alert: 

#pragma mark - 
#pragma mark UITextFieldDelegate 

- (BOOL)textFieldShouldReturn:(UITextField *)textField 
{ 
    if ([self acceptsEntry:textField.text]) { // this checks if the text is valid 
     // We're done here 
     return YES; 
    } else { 
     // Setting the delegate to nil will prevent the textField to listen for Return key events. 
     textField.delegate = nil; 

     // Removing the observer will prevent the user from typing into the textfield using an external keyboard 
     [textField resignFirstResponder]; 

     currTextField = textField; 

     UIAlertView *av = [[UIAlertView alloc] initWithTitle:NSLocalizedString(@"invalidEntry", @"") 
                message:NSLocalizedString(@"invalidEntryMessage", @"") 
                delegate:self 
              cancelButtonTitle:NSLocalizedString(@"OK", nil) otherButtonTitles:nil]; 
     [av show]; 
     [av release]; 
    } 
    return NO; 
} 

#pragma mark - 
#pragma mark UIAlertViewDelegate 

- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex 
{ 
    // gets called when the user dismisses the alert view 
    currTextField.text = @""; // erase bad entry 
    currTextField.delegate = self; // We want to listen for return events again 
    [currTextField becomeFirstResponder]; 
    currTextField = nil; 
}