UITextField的文本框部分文本以*的方式来显示

 #import "AppDelegate.h"

 @interface AppDelegate ()<UITextFieldDelegate>// 添加代理协议

 @end

 @implementation AppDelegate

 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
     self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
     // Override point for customization after application launch.
     self.window.backgroundColor = [UIColor whiteColor];

     UITextField *tf = [[UITextField alloc] initWithFrame:CGRectMake(, , , )];
     //确认代理
     tf.delegate = self;
     tf.keyboardType = UIKeyboardAppearanceDefault;

     tf.backgroundColor = [UIColor greenColor];
     [self.window addSubview:tf];

     [self.window makeKeyAndVisible];
     return YES;
 }

 - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
 {
     int length = [textField.text length];
     // 2代表*号的起始位置,9代表*号的结束位置
     if (length >  && length < ) {
         NSMutableString *text = [textField.text mutableCopy];
         [text replaceCharactersInRange:NSMakeRange(length -  , ) withString:@"*"];
         textField.text = text;
     }
     return YES;
 }

 @end

实现的效果如下图：