C#•8mo ago

[WPF]How to binding in the UserControl.xaml at the same time load UserControl.xaml UI?

I'm using the wpf-ui template to use the wpf mvm pattern. I focused on 4 files I want to use DashboardPage.xaml, DashboardPageViewModel.cs , User.xaml, UserViewModel.cs . I want to get the ui of the UserControl file User.xaml from the Page file DashboardPage.xaml. By the way, I implemented a code that allocates datacontext to the behind code to implement a button-like control function in User.xaml. Of course, I implemented the same code that allocates DataContext to the DashboardPage.xaml.cs behind code. The problem is that the code implemented by User.xaml.cs causes the "Object reference not set to an instance of an object." error. I wonder why the problem occurred. *picture 1 is error cature. **picture2 is that if annotate ViewModel assign part and DataContext assign part in the User.xaml.cs , then no happened error. but this is not what i want. I wanna implement control at the UserControl.xaml ( User.xaml) How to solve this problem. and Why did the error occur? below is code. https://github.com/Jlim01/UiDesktopApp1.git

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GitHub - Jlim01/UiDesktopApp1

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21 Replies

JJOP•8mo ago

If you can't enter github, then You can download this text file and see six code included View.xaml/Viewxaml.cs / ViewModel.cs

code.txt

leowest•8mo ago

its complaining your User.xaml.cs does not have an accessible constructor

    public partial class User : UserControl
    {
        public User()
        {
            InitializeComponent();
        }
    }

    public partial class User : UserControl
    {
        public User()
        {
            InitializeComponent();
        }
    }

<UserControl x:Class="UiDesktopApp1.Views.User.User"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:UiDesktopApp1.Views.User"
             xmlns:vm="clr-namespace:UiDesktopApp1.ViewModels.User"
             mc:Ignorable="d" 
             Background="White"
             d:DataContext="{d:DesignInstance local:User}"
             d:DesignHeight="120" d:DesignWidth="300">
    <UserControl.DataContext>
        <vm:UserViewModel/>
    </UserControl.DataContext>
    <Grid>
        <StackPanel>
            <Button Content="btn" Width="80" Height="50"                    
                    Command="{Binding onBtnCommand}"></Button>
            <TextBlock Text="{Binding Cnt, Mode=TwoWay}"/>
        </StackPanel>

    </Grid>
</UserControl>

<UserControl x:Class="UiDesktopApp1.Views.User.User"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:UiDesktopApp1.Views.User"
             xmlns:vm="clr-namespace:UiDesktopApp1.ViewModels.User"
             mc:Ignorable="d" 
             Background="White"
             d:DataContext="{d:DesignInstance local:User}"
             d:DesignHeight="120" d:DesignWidth="300">
    <UserControl.DataContext>
        <vm:UserViewModel/>
    </UserControl.DataContext>
    <Grid>
        <StackPanel>
            <Button Content="btn" Width="80" Height="50"                    
                    Command="{Binding onBtnCommand}"></Button>
            <TextBlock Text="{Binding Cnt, Mode=TwoWay}"/>
        </StackPanel>

    </Grid>
</UserControl>

JJOP•8mo ago

 public UserViewModel ViewModel { get; }
 public User(UserViewModel viewModel)
 {

   InitializeComponent();
   ViewModel = viewModel;
   DataContext = this;

 }

 public UserViewModel ViewModel { get; }
 public User(UserViewModel viewModel)
 {

   InitializeComponent();
   ViewModel = viewModel;
   DataContext = this;

 }

this code is wrong code?

leowest•8mo ago

yes because the way your useing the usercontrol it cannot be initialized so instead u sets the datacontext via xaml

JJOP•8mo ago

Actually Im following "WPF-UI" Template . so I thought UserControl also is the same code with Page code

leowest•8mo ago

if u wanted to use it like that u would need to use a ContentControl to load the control by its vm you're not using it in the same way the page code is being used in a presenter the usercontrol ur loading directly

JJOP•8mo ago

yea actually I don't know how to use that..

JJOP•8mo ago

presenter you are saying is this part?

leowest•8mo ago

JJOP•8mo ago

thanks your kind reply ! , but Im wandering how to know that ContentPresenter is related to Page files like DashboardView.xaml It's so difficult for me <ContentPresenter x:Name="RootContentDialog" Grid.Row="0" /> because I thought This code is not anything I just delete <ContentPresenter x:Name="RootContentDialog" Grid.Row="0" /> this code , and then executed program. the result is no problem...

leowest•8mo ago

my bad yeah that does nothing the navigationview the RootNativation resolves what page to load which is handled by your navigation service but for the usercontrol your directly inserting it to xaml <user:User Grid.Row="1"/> so it does not understand how initialize so u would either use a ContentControl and resolve it like u do for pages or u simple have the datacontext applied to xaml since it will just instantiate it for u when constructed it can use it

JJOP•8mo ago

is there any tutorial or sample code? resolving using ContentControl.

leowest•8mo ago

I dont know of any no sorry.

JJOP•8mo ago

nono, That's already enough answer. thanks!

MODiX•8mo ago

Use the /close command to mark a forum thread as answered

JJOP•8mo ago

I send to you message,

leowest•8mo ago

send it here, I dont take dms

JJOP•8mo ago

I want to send a coffee coupon to you. What should I do?

leowest•8mo ago

its ok we don't do this for compensation its also against the rules to offer compensation everyone is here to learn and to help.

JJOP•8mo ago

thank you, If I become an expert, I will be of help to others like you.

leowest•8mo ago

u dont need to be an expert to help 😉 I am definitively not one either

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[WPF]How to binding in the UserControl.xaml at the same time load UserControl.xaml UI?