WPF窗口未使用XAML中的绑定更新

Question

Can someone please explain what's going on here? I'm new to WPF and migrating my Forms project to WPF with binding. I'm using AvalonDock but I'm not binding directly to any of the AvalonDock controls. Here's a couple excerpts. I removed a lot for brevity's sake but let me know if you need to see something else.

EDIT: These two StackPanels are just tests... trying to figure this stuff out.
EDIT2 : I'm trying to do MVVM eventually; I just need to get a better handle on binding so I know how to structure it.
EDIT3 : See bottom of post.

Q: The first StackPanel does not update at all, never mind updating after changes. I've tried setting the DataContext in the StackPanel , Grid and TextBlock . What am I doing wrong?

Q: The second works fine when the parent grid is bound in code behind but only if bound where you see it, not in the MainWindow_Loaded() method. What's different here?

I've read several tutorials as well as plenty of similar questions here but nothing's helping me understand what the difference is here and what I'm missing.

<Window x:Class="TestUIWPF.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:ad="http://schemas.xceed.com/wpf/xaml/avalondock"
        Title="MainWindow" Height="768" Width="1024"
        Loaded="MainWindow_Loaded"
        xmlns:vm="clr-namespace:TestUIWPF.ViewModel"
        >
<!-- lots excluded for brevity. there are no Window.Resources -->
<ad:LayoutAnchorable Title="Test" >
    <Grid x:Name="gridTest">
        <StackPanel Orientation="Vertical">
            <StackPanel Orientation="Horizontal">
                <StackPanel.DataContext>
                    <vm:EntityViewModel />
                </StackPanel.DataContext>
                <TextBlock Text="Label" />
                <TextBlock DataContext="{Binding ActiveEntity}" Text="{Binding Path=Label}" />
            </StackPanel>

            <StackPanel Orientation="Horizontal" >
                <TextBlock Text="Label Again" />
                <TextBlock Text="{Binding Path=Label}" />
            </StackPanel>
        </StackPanel>
    </Grid>
</ad:LayoutAnchorable>

private void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
    this.DataContext = this;
    SelectedEntityViewModel = new ViewModel.EntityViewModel();
    ImportEntityXML_Click(null, null); //skips clicking the menus
}
private void ImportEntityXML_Click(object sender, RoutedEventArgs e)
{
    //omitted OpenFileDialog and XmlReader stuff
    xmlreader = new XmlReader(dlg.FileName);
    Entities.Add(xmlreader.ReadEntityFromXML());
    SimulatedEntitySelection(Entities.ElementAt(0)); //haven't built any of the UI stuff for this yet
}

private void SimulatedEntitySelection(Entity ent)
{
    SelectedEntityViewModel.ActiveEntity = ent;
    gridTest.DataContext = SelectedEntityViewModel.ActiveEntity;
}

private void button_Click(object sender, RoutedEventArgs e) 
{
    SelectedEntityViewModel.ActiveEntity.Label = "test";
}

Entity and EntityViewModel implement INotifyPropertyChanged and it works just fine with the second StackPanel . The button that calls button_Click() is just for testing the binding. EntityViewModel pretty much just wraps Entity through the ActiveEntity property and helps with reading the collections-of-collections within Entity .

EDIT3:

I've also tried a couple resources. Here's how I did the ObjectDataProvider:

<Window.Resources>
    <ObjectDataProvider x:Key="testVM" ObjectType="{x:Type vm:EntityViewModel}" />
    <vm:EntityViewModel x:Key="SelEntVM" />
</Window.Resources>
<!-- .... -->
<StackPanel.DataContext>
    <Binding Source="{StaticResource testVM}" />
</StackPanel.DataContext>
<TextBlock Text="Label" />
<TextBlock Text="{Binding Path=ActiveEntity.Label}" />

Answer 1

It does work. You might be probably updating a wrong viewmodel.

Once you define the viewmodel in DataContext , youd have to access it this way:

private void button_Click(object sender, RoutedEventArgs e) 
{
    var myModel = (ViewModel.EntityViewModel)(yourStackPanelName.DataContext);
    myModel.ActiveEntity.Label = "test";
}

Answer 2

Your first stack panel is not working, because the data context is inherited. Therefore, once you change the DataContext of the Grid to the ActiveEntity object, the binding on the text block in the first data context will set the datacontext for the TextBlock to the ActiveEntity on the current datacontext, which would already be the ActiveEntity (therefore ActiveEntity.ActiveEntity ) And than try to bind to the Label property on that. Eg ActiveEntity.ActiveEntity.Label

Before the click, you are setting the DataContext of that window to "this" which I am assuming is not the ViewModel, it is the code behind?

If you are using MVVM,

you should have something like this

private void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
    SelectedEntityViewModel = new ViewModel.EntityViewModel();
    this.DataContext = SelectedEntityViewModel;
    ImportEntityXML_Click(null, null); //skips clicking the menus
}

Or some other ViewModel which provides all the necessary data.

You nomrally would have a MainWindowView and MainWindowViewModel , at least that is the convention and usually you set the datacontext of the window in the constructor once(you can do it in the Loaded handler), in most cases you shouldn't need to manually change the DataContext of any framework elements in the code behind.

EDIT: Example Code:

MainWindow.xaml

<Window x:Class="SO27760357.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="300" Width="300">
    <Grid>
        <StackPanel Orientation="Vertical">
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="Label" />
                <TextBlock Text="{Binding ActiveEntity.Label}"/>
            </StackPanel>

            <StackPanel Orientation="Horizontal">
                <TextBlock Text="Label Again" />
                <TextBlock Text="{Binding ActiveEntity.Label}" />
            </StackPanel>
        </StackPanel>
    </Grid>
</Window>

MainWindow.xaml.cs

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = new MainWindowViewModel();
    }
}

MainWindowViewModel.cs (INotifyPropertChanged omitted for simplicity)

public class MainWindowViewModel
{
    public EntityViewModel ActiveEntity { get; set; }
}

EntityViewModel.cs (INotifyPropertChanged omitted for simplicity)

public class EntityViewModel
{
    public string Label { get; set; }
}

As you can see, I am setting the DataContext of the Window to the MainViewModel, therefore the DataContext(root of all bindings) is the MainViewModel, and each TextBlock needs to first access the ActiveEntity property first, before it can get to the Label proeprty.

THe other option is, that if everything inside the main stack panel you given us, will be bound to ActiveEntity, you can change the DataContext of that StackPanel, binding it to the ActiveEntity , and therefore all of its children datacontext will also be that object.

    <StackPanel Orientation="Vertical"
                **DataContext="{Binding ActiveEntity}"**>
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="Label" />
            <TextBlock **Text="{Binding Label}"**/>
        </StackPanel>

        <StackPanel Orientation="Horizontal">
            <TextBlock Text="Label Again" />
            <TextBlock **Text="{Binding Label}"** />
        </StackPanel>
    </StackPanel>

EDIT 2 - Advice

You should refrain from referencing objects by name as much as possible, and have as little logic in the code behind as possible, if any. For most simple screens there is no need to have anything in code behind other than the initial Binding of the DataContext (if you don't have a window service which creates + sets the DataContext of windows)