Using reflection to dynamically create ViewModel to implement a single example under MVVM

In the case of MVVM, you would expect ViewModel to have only one instance of the entire application. The traditional practice is to use singleton mode to implement:

public class Viewmodeltest
{
Private Viewmodeltest ()
{

}

private static Viewmodeltest Viewmodelinstace;

public static Viewmodeltest Getviewmodeltestinstace ()
{
if (Viewmodelinstace = = null)
{
Viewmodelinstace = new Viewmodeltest ();
}
return viewmodelinstace;
}
}

It's a traditional singleton pattern, but we're going to have a lot of viewmodel at the time of development. If every viewmodel is going to implement a single-instance mode, the workload is a huge project. So here is the use of reflection to provide a simple and common way to implement the code as follows:

A: First Onstartup event in App.xaml.cs declares a global dictionary collection for storing our ViewModel

protected override void Onstartup (StartupEventArgs e)
{
Base. Onstartup (e);

Creating a ViewModel Global map
application.current.properties["Viewmodelmap"] = new dictionary<string, object> ();
}

Second: Using reflection to dynamically create ViewModel

  Public classViewmodelfactory { Public Static ObjectGetviewmodel (Type vm_type) {Dictionary<string,Object> dic = application.current.properties["Viewmodelmap"] asdictionary<string,Object>; if(DIC. ContainsKey (Vm_type. FullName)) {returnDic[vm_type.            FullName]; }            Else            {ObjectNEW_VM =Activator.CreateInstance (Vm_type); Dic. ADD (Vm_type.                FullName, NEW_VM); returnNEW_VM; }        }

Three: Call the Getviewmodel method directly when assigning DataContext to a view

 Public class viewmodeltest    {        private  viewmodeltest ()         {                 }    }

 Public Partial class viewmodeltestwindow:window{   　public  Window ()     {        this. InitializeComponent ();         this. DataContext = Viewmodelfactory.getviewmodel (typeof(viewmodeltest));      }}

Using reflection to dynamically create ViewModel to implement a single example under MVVM