Question

code snippet:

xaml

<TextBlock Grid.Row="0"  Text="{Binding Path=NodeType}"></TextBlock>
<Button Name="bt" Grid.Row="1" Click="bt_Click">click</Button>

c#

public FamilyMemberInfo MemberInfo;
public MainWindow()
{
    InitializeComponent();

    MemberInfo = new FamilyMemberInfo();
    MemberInfo.NodeType = "aa";
    this.DataContext = MemberInfo;
}
private void bt_Click(object sender, RoutedEventArgs e)
{
    //MemberInfo.NodeType = "bb";
    FamilyMemberInfo mi2 = new FamilyMemberInfo();
    mi2.NodeType = "bb";
    MemberInfo = mi2; 
}

If I change the NodeType to ‘bb’, the textblock is changed too, but if I create a bland new object and set the property NodeType to ‘bb’, then assign it to MemberInfo, the textblock is not updated. could anyone explain that for me? thanks in advance.

And say that the class ‘FamilyMemberInfo’ has 20 properties, all are binding with elements(textblock, combobox, etc) on the UI, and I get an instance of FamilyMemberInfo from some other place, I want to simply assign it to the MemberInfo as code above to make the UI update accordingly, how to make it work?

Thanks.

Answer 1

You have to set DataContext to the new instance you created.

private void bt_Click(object sender, RoutedEventArgs e) 
{ 
    //MemberInfo.NodeType = "bb"; 
    FamilyMemberInfo mi2 = new FamilyMemberInfo(); 
    mi2.NodeType = "bb"; 
    MemberInfo = mi2; 
    this.DataContext = MemberInfo; // you have to add this line to the code
} 

The reason is when you set this.DataContext = MemberInfo; inside the constructor, it points to the object you created in the constructor, let’s name it object A.

Now you set MemberInfo = mi2, mi2 is a difference object and you set MemberInfo to point to mi while object A that you created (inside the constructor) is still there and this.DataContext is still point to that object.

So, you have to set DataContext to point to the new object as in above code.