The article says how to use one/more ViewMiodels in a View. Also, multiple Views using same ViewModel. Read this post to create a ViewModel.
There are several ways of using ViewModel in a XAML file based on the different scenarios.
Case 1: Initialize a ViewModel without any constructor parameters.
Read this post. This article also expects the reader to be familiar with Expression Blend.
Case 2: Initialize a ViewModel with constructor parameters.
xmlns:local="clr-namespace:****your namespace***"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
<ObjectDataProvider ObjectType="{x:Type local:ViewModel}" x:Key="theViewModel"> <ObjectDataProvider.ConstructorParameters>
<sys:String>Uday</sys:String>
<sys:Int32>25</sys:Int32>
</ObjectDataProvider.ConstructorParameters>
</ObjectDataProvider>
Notice the System namespace declaration. We can use any data type from System namespace as a constructor parameter. If you have custom data types you can pass them too as a constructor parameter; by declaring namespace in XAML file.
Case 3: In the above two cases, the object can be accessed on the C# side (as a Resource). However, if you update the object in C# side, the ViewModel values are NOT reflected on the XAML side. Now what??! We can declare a ViewModel object on the C# side and declare it as DataContext for the XAML side. Here is how to do it.
public partial class MainWindow : Window
{
private ViewModel theViewModel = new ViewModel();
public MainWindow()
{
InitializeComponent();
this.DataContext = theViewModel;
}
private void TextBox_TextChanged(object sender, System.Windows.Controls.TextChangedEventArgs e)
{
theViewModel.FirstName = "I am still typing";
}
}
In this way, any updates from XAML side would be seen on C# side too. But, if you use Expression Blend, the ViewModel is not seen in the designer, so you have to write the binding code manually. I wouldn’t suggest this way, but sometime its not up to your choice!
