securetextentry 切换后有空格问题解决

搜索发现这个问题，网上的解决方法不明确，对于小白怎么办

直接上代码：

- (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;

    }
}