Question

我正在使用c＃xaml开发Windows手机应用程序我正在使用MVVM架构。

我有两个View Model类

BaseViewModel:ViewModelBaseX
{
  public override void OnNavigatedTo(NavigationMode mode, Uri uri, IDictionary<string, string> queryString)
  {
     // a condition is checking here & if the condition is true ,  
        i don't want to run the remaining codes in the AboutViewModel .

     TOTO: have to stop the execution here & prevent execution
           of remaining codes in the derived classes.
  }
}

AboutViewModel:BaseViewModel
{
  public override void OnNavigatedTo(NavigationMode mode, Uri uri, IDictionary<string, string> queryString)
  {
      base.OnNavigatedTo(mode, uri, queryString);                

      // here some code to be execute 

  }
}

我知道在baseviewmodel＆amp;中设置属性标志的方法。在派生的视图模型中检查它但它会使代码重复和必须在所有派生类中检查它。

还有其他方法可以从基类中找到它吗？请帮忙！

Answer 1

一种选择是将所有实际的OnNavigatedTo代码放在由基类OnNavigateTo调用的单独方法中。在基类上创建它作为受保护的方法（可能不做任何事情）并在派生类上重写它。然后基类只在它想要的时候调用它。

BaseViewModel:ViewModelBaseX
{
  public override void OnNavigatedTo(NavigationMode mode, Uri uri, IDictionary<string, string> queryString)
  {
     // a condition is checking here & if the condition is true ,  
        i don't want to run the remaining codes in the AboutViewModel .
    if (someCondition)
    {
        NavigateToFunctionality();
    }
    else
    {
      // do nothing
     }
  }

  protected void NavigateToFunctionality()
  {
  }

}

AboutViewModel:BaseViewModel
{
  public override void OnNavigatedTo(NavigationMode mode, Uri uri, IDictionary<string, string> queryString)
  {
      base.OnNavigatedTo(mode, uri, queryString);                

  }

  protected override void NavigateToFunctionality()
  {
    // your code goes here
  }
}

Answer 2

最简单的方法是：

1 /在BaseViewModel中引入一个新的虚拟方法（称为＆＃34; HandleNavigatedTo＆＃34;）

2 /有BaseViewModel调用＆＃34; HandleNavigatedTo＆＃34;根据您的标准

3 /让BaseViewModel后代覆盖＆＃34; HandleNavigatedTo＆＃34;并用那种方法做他们的东西

4 /让BaseViewModel后代 NOT 覆盖＆＃34; OnNavigatedTo＆＃34;

public class BaseViewModel : ViewModelBaseX
{


       protected virtual void HandleNavigatedTo(NavigationMode mode, Uri uri, IDictionary<string, string> queryString)
        {
        }

        public override void OnNavigatedTo(NavigationMode mode, Uri uri, IDictionary<string, string> queryString)
        {
            if (condition)
            {
                HandleNavigatedTo(mode, uri, queryString);
             }
        }
    }

    public class AboutViewModel:BaseViewModel
    {
          public override void HandleNavigatedTo(NavigationMode mode, Uri uri, IDictionary<string, string> queryString)
          {
              // here some code to be execute 
          }
     }

如何在Windows Phone中从它的基类实现中断执行覆盖方法？

2 个答案: