这时候可以添加如下代码：

[alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
// 可以在这里对textfield进行定制，例如改变背景色
textField.backgroundColor = [UIColor orangeColor];
}];

 

完整的密码输入：

- (void)showSecureTextEntryAlert {
NSString *title = NSLocalizedString(@"A Short Title Is Best", nil);
NSString *message = NSLocalizedString(@"A message should be a short, complete sentence.", nil);
NSString *cancelButtonTitle = NSLocalizedString(@"Cancel", nil);
NSString *otherButtonTitle = NSLocalizedString(@"OK", nil);

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];
[alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleTextFieldTextDidChangeNotification:) name:UITextFieldTextDidChangeNotification object:textField];
textField.secureTextEntry = YES;
}];
UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:cancelButtonTitle style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
NSLog(@"The \"Secure Text Entry\" alert's cancel action occured.");
[[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:alertController.textFields.firstObject];
}];

UIAlertAction *otherAction = [UIAlertAction actionWithTitle:otherButtonTitle style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
NSLog(@"The \"Secure Text Entry\" alert's other action occured.");
[[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:alertController.textFields.firstObject];
}];

// The text field initially has no text in the text field, so we'll disable it.
otherAction.enabled = NO;
// Hold onto the secure text alert action to toggle the enabled/disabled state when the text changed.
self.secureTextAlertAction = otherAction;

[alertController addAction:cancelAction];
[alertController addAction:otherAction];

[self presentViewController:alertController animated:YES completion:nil];
}

注意四点：

1.添加通知，监听textfield内容的改变：

// Add the text field for the secure text entry.
[alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
// Listen for changes to the text field's text so that we can toggle the current
// action's enabled property based on whether the user has entered a sufficiently
// secure entry.
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleTextFieldTextDidChangeNotification:) name:UITextFieldTextDidChangeNotification object:textField];

textField.secureTextEntry = YES;
}];
2.初始化时候，禁用“ok”按钮：

otherAction.enabled = NO;

self.secureTextAlertAction = otherAction;//定义一个全局变量来存储

 

3.当输入超过5个字符时候，使self.secureTextAlertAction ＝ YES：

- (void)handleTextFieldTextDidChangeNotification:(NSNotification *)notification {
UITextField *textField = notification.object;
// Enforce a minimum length of >= 5 characters for secure text alerts.
self.secureTextAlertAction.enabled = textField.text.length >= 5;
}
4.在“OK”action中去掉通知：

UIAlertAction *otherAction = [UIAlertAction actionWithTitle:otherButtonTitle style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
NSLog(@"The \"Secure Text Entry\" alert's other action occured.");

// Stop listening for text changed notifications.
[[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:alertController.textFields.firstObject];
}];