密码输入框从密文切到明文，后面会出现空格

点击开关进行输入框明密文切换

becomeFirstResponder可使密文变明文时，显示的字符串后面没空格

if ([sender isKindOfClass:[TTFadeSwitch class]]) {//密码显示开关
        TTFadeSwitch *sw = sender;
        if (!sw.on) {
            self.passwordField.secureTextEntry = true;
            
        }else{
            self.passwordField.secureTextEntry = false;
            [self.passwordField becomeFirstResponder];
        }
    }