C#•2mo ago

Wrong DataContext Inference?

First of all I am still a beginner, so I might not completely know what I am saying. So I am building an Avalonia MVVM app, it is an inventory management system. I have used Postgres for the database. The problem here is, in InventoryView, the commands to edit and delete rows can not be resolved. Rider tells me that the datacontext for the commands is InventoryView, which should be InventoryViewModel, if I am right? I am very new to Avalonia, and only familiar with Winforms, which a lot different.

15 Replies

ero•2mo ago

where do you set the datacontext?

voideyOP•2mo ago

In InventoryView, <UserControl xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:vm="using:IMS.ViewModels" x:DataType="vm:InventoryViewModel" x:Class="IMS.Views.InventoryView">

ero•2mo ago

mh, i'm not sure where you're setting datacontext here

MODiX•2mo ago

Klarth

x:DataType is to enforce type safety for compiled bindings.

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voideyOP•2mo ago

Oh, so that means, I need to define it in the code behind, right?

ero•2mo ago

you don't, luckily :)

<UserControl.DataContext>
  <vm:InventoryViewModel />
</UserControl.DataContext>

<UserControl.DataContext>
  <vm:InventoryViewModel />
</UserControl.DataContext>

voideyOP•2mo ago

thanks, let me try that.

voideyOP•2mo ago

still no luck, I am quite puzzled on why it is inferred rightly here but not in the datagrid?

ero•2mo ago

at this point i would direct the question to #gui. either close this post or link to here with a short summary of the issue (we don't like crossposting)

voideyOP•2mo ago

okay, will do thanks @ero

Insire•2mo ago

can you post your InventoryViewModel and InventoryItem ? the properties are enough

voideyOP•2mo ago

Hey thanks, I slept on the project for a while and fixed the issue using explicit casting to InventoryViewModel, like this:

<Button Content="Edit"
                                        Command="{Binding 
                                        ((vm:InventoryViewModel)DataContext).EditItemCommand, 
                                        RelativeSource={RelativeSource AncestorType=DataGrid}}"
                                        CommandParameter="{Binding}" />

<Button Content="Edit"
                                        Command="{Binding 
                                        ((vm:InventoryViewModel)DataContext).EditItemCommand, 
                                        RelativeSource={RelativeSource AncestorType=DataGrid}}"
                                        CommandParameter="{Binding}" />

voideyOP•2mo ago

Here it is

message.txt

Nasdack•2mo ago

the DataContext inside a DataTemplate isn't inferred from its parent control, which is InventoryView.axaml in your case. you can set a name for your view and use that name as ElementName in your binding parameters, or you can use some special syntax to explicity specify the data binding context, like here: https://github.com/AvaloniaUI/Avalonia/discussions/11339

GitHub

Binding to "parent" data context in ItemsRepeater · AvaloniaUI Aval...

I want to bind some elements of a data item template NOT to items data context but to the "parent" kind of data context. In below sample specifically to a command in the general data cont...

voideyOP•2mo ago

Oh thanks, that is exactly what I used here.

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Wrong DataContext Inference?