- (void)viewDidLoad {

    [super viewDidLoad];

    self.view.backgroundColor = [UIColor whiteColor];

    UITextField *test = [[UITextField alloc]initWithFrame:CGRectMake(, , , )];

    test.placeholder = @"输入帐号";

    test.secureTextEntry = YES;

    self.test = test;

    [self.view addSubview:test];

}

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event

{

    if (self.test.secureTextEntry) {

        NSString *str =self.test.text;

        self.test.text =@"";

        self.test.secureTextEntry = NO;

        self.test.text = str;

    }else{

        NSString *str =self.test.text;

        self.test.text =@"";

        self.test.secureTextEntry = YES;

        self.test.text = str;

    }

}