ContentControl.Content设置程序始终会覆盖内容模板的内容

Question

I am fighting with this issue for at least a couple of hours already. I tried all possible solution I found on the net. My latest is below and you will see that I am trying to add a simple MenuBar to the main Window control and present the content beneath. My application is using MVVM and the view is assigned like this:
myMainWindow.Content = view; // this is what I cannot change

The soultion should be trivial but none works. I tried with ContentTemplate, ContentPresenter, Style setter, all the variations with binding but nothing works as expected that is whenever myMainWindow.Content menu bar disappears.

None of the samples available on the internet does not actaully show an application with MenuBar and content at the same time.

Is it so hard to add a menu bar in WPF application? I would be more than happy for any new suggestions.
Thanks in advance.

<window:BaseWindow x:Class="OneTwoThree.Manager.MainWindow"
                   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                   xmlns:window="clr-namespace:Xsell.Client.Common;assembly=Xsell.Client.Common"
                   Title="{Binding Title}"
                   Width="1020"
                   Height="750"
                   Closed="AppClosed"
                   Icon="app.ico"
                   Loaded="AppLoaded">
    <Window.Resources>
        <Style TargetType="{x:Type Window}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type Window}">
                        <Grid>
                            <DockPanel>
                                <Menu IsMainMenu="True" DockPanel.Dock="Top">
                                    <MenuItem Header="Admin">
                                        <MenuItem Header="Manage Labels"></MenuItem>
                                    </MenuItem>
                                </Menu>
                                <ContentPresenter DockPanel.Dock="Bottom"/>
                            </DockPanel>
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>
</window:BaseWindow>

Answer 1

Your application isn't really using MVVM. At best it might be sort of halfway using MVVM.

Meanwhile, all the XAML inside your <Window> tag in your main window XAML file is the window's Content . And you are explicitly replacing that with some random object, so of course it's not there any more.

You aren't giving much detail, but you need to assign your main viewmodel to the Window's DataContext and not assign anything to the window's Content .

You didn't say what view is in this line of code, so I have no idea what you were trying to do there:

myMainWindow.Content = view; // this is what I cannot change

Is view a viewmodel, or a view? Whatever it is, don't do that.

You could assign your main viewmodel to the Window's datacontext in XAML, too:

<Window ... >

<Window.DataContext>
    <local:MyViewModel />
</Window.DataContext>

<!-- ... -->

</Window>

Then bind your viewmodel to the Content property of a ContentPresenter . There's no need to apply the window's content via a template here so I eliminated that part. The only template you need in this snipppet is the DataTemplate which displays your viewmodel in the ContentPresenter .

The layout here is copied verbatim from MainWindow.xaml in a project I recently wrote. I replaced my main menu with yours and omitted my Window.Resources . That's the only change.

<Window ...>
    <DockPanel>
        <Menu IsMainMenu="True" DockPanel.Dock="Top">
            <MenuItem Header="Admin">
                <MenuItem Header="Manage Labels"></MenuItem>
            </MenuItem>
        </Menu>
        <Grid>
            <ContentPresenter 
                Content="{Binding}"
                />
        </Grid>
    </DockPanel>
</Window>

A simple {Binding} with no Source or Path etc. properties will bind to the DataContext . The ContentPresenter will inherit its DataContext from the Window that contains it.

Then, if you've got a data template defined with a DataType the same as your main viewmodel, that data template will be instantiated in that ContentPresenter .

"Bind" doesn't mean "assign in code-behind". It means to use the System.Windows.Data.Binding class. The easiest way to do that is in the XAML as I've shown above.