分享一种mvvm弹出子窗体的方式

其实逻辑很简单，在前端的cs中注册子窗体，在viewmodel中resolve并show出来。这需要通过一个子窗体注册类来进行操作。这种弹出子窗体的方式，我们用到了mef框架。将导出的子窗体注册类分别导入到WindowBase和ViewModelBase，且他们是同一个实例。
我们定义一个子窗体操作类。
<pre>
[Export]
public class UIShowManager
{

     private readonly Hashtable _registeredWindowsEx = new Hashtable();
       public void Register(string key, Type t)
    {
        _registeredWindowsEx.Add(key, t);
    }
    public void Register<T>(string key)
    {
        _registeredWindowsEx.Add(key, typeof(T));
    }
    public void Show(string key, object vm)
    {
        Window win = CreateWindow(key, vm );
        if (win != null)
        {
            win.Show();
        }
    }

    public void ShowDialog(string key, object vm)
    {
        Window win = CreateWindow(key, vm);
        if (win != null)
        {
            win.ShowDialog();
        }
    }

    private Window CreateWindow(string key, object vm)
    {
        if (!_registeredWindowsEx.ContainsKey(key))
            throw new Exception("不存在这个key");

        object obj = _registeredWindowsEx[key];

        Type windowType;
        if (obj is Type)
        {
            windowType = obj as Type;
        }
        else if (obj is Window)
        {
            windowType = typeof(object);
        }
        else
        {
            throw new Exception("这个key对应的元素不是窗体！");
        }

       var window=(Window) Activator.CreateInstance(windowType);

       if (vm != null)
       {
           window.DataContext = vm as ViewModelBase;
       }

       return window;
    }
}

</pre>
我们将这个类导出。

因为用到了Mef，我们增加一个MefHelper。
<pre>
public class MefHelper
{

   private static MefHelper _singleton=new MefHelper ();
   private CompositionContainer container;
   public MefHelper()
   {
       //AggregateCatalog用来合并多个catalog
       var catalog = new AggregateCatalog();

       AssemblyCatalog assemblyCatalog = new AssemblyCatalog(Assembly.GetEntryAssembly());
       DirectoryCatalog directoryCatalog = new DirectoryCatalog(AppDomain.CurrentDomain.BaseDirectory);
       catalog.Catalogs.Add(assemblyCatalog);
       catalog.Catalogs.Add(directoryCatalog);
       container = new CompositionContainer(catalog);
   }

   public static MefHelper Instance
   {
       get { return _singleton; }
   }
 

   public   void Compose(object obj)
   {
       container.ComposeParts(obj);
   }

   public void ComposeOnce(object obj)
   {
       container.SatisfyImportsOnce(obj);
   }
}

</pre>

然后我们建个WindowBase，没有WindowBase，也可以直接写在View中。并导入UIShowManager。
<pre>
public class WindowBase: Window
{

  [Import]
  public UIShowManager _UIShowManager = null;

}

</pre>

我们在建一个ViewBase，并导入UIShowManager
<pre>
public partial class ViewModelBase : INotifyPropertyChanged
{
[Import]
private UIShowManager _UIShowManager = null;
public ViewModelBase()
{

    }

    public void Show(string key,object vm)
    {
        if (_UIShowManager == null)
            MefHelper.Instance.Compose(this);

        _UIShowManager.Show(key,vm);
    }

    public void ShowDialog(string key, object vm)
    {
        if (_UIShowManager == null)
            MefHelper.Instance.Compose(this);

        _UIShowManager.ShowDialog(key, vm);
    }

    #region 【实现接口】
    public event PropertyChangedEventHandler PropertyChanged;
    public void RaisePropertyChanged(string name)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(name));
        }
    }


    #endregion
}

</pre>
ViewModelBase中有两个方法，Show和ShowDialog，用来显示子窗体。

好了，基本的框架已经搭好了，下面我们进行测试。
我们按照MVVM的方式，添加一些窗体和VM，如下图所示。

image.png

<pre>
public partial class MainWindow :WindowBase
{
public MainWindow()
{
InitializeComponent();

        if (_UIShowManager == null)
            MefHelper.Instance.Compose(this);

        this.DataContext = new VM();

        _UIShowManager.Register("aaa",typeof(ChildWindow));
    }
}

</pre>
MainWindow继承WindowBase。在此界面里注册需要显示的子窗体。注册方法是_UIShowManager.Register("aaa",typeof(ChildWindow));

<pre>
public class VM : ViewModelBase
{
public VM()
{
ShowChildCommand = new DelegateCommand(ExecuteShowChild);
}

    public DelegateCommand ShowChildCommand { get; set; }


    private string _ChildCaption = "这是子窗体";

    public string ChildCaption
    {
        get { return _ChildCaption; }
        set { _ChildCaption = value; RaisePropertyChanged("ChildCaption"); }
    }


    private void ExecuteShowChild()
    {
       ShowDialog("aaa",this);
    }
}

</pre>
vm继承ViewModelBase，弹出子窗体，调用父类的ShowDialog方法。
这样我们在主窗体中点击按钮，就可以弹窗了。

image.png