BZGFormField is a text field with a validity indicator. UI/UX inspired by @muffs

The left indicator changes color based on the validity of the field's text - just pass the field a text validation block:

[self.passwordField setTextValidationBlock:^BOOL(NSString *text) {
    return (text.length >= 8);
}];

When the text field returns, the indicator expands and becomes tappable.

When the indicator is tapped, an alert view is displayed - you can configure the alert view in the text validation block.

__weak RootViewController *weakSelf = self;
[self.passwordField setTextValidationBlock:^BOOL(NSString *text) {
    if (text.length < 8) {
        weakSelf.passwordField.alertView.title = @"Password is too short";
        return NO;
    } else {
        return YES;
    }
}];

If you're using cocoapods, add pod 'BZGFormField' to your Podfile. Otherwise, add BZGFormField/BZGFormField.h and BZGFormField/BZGFormField.m to your project.

Check out the sample Xcode project in Example