WPF Binding dynamic control in code behind to ViewModel - wpf

Question

I'm building a custom UserControl in WPF, which has a ViewModel associated. I also want do dynamically make controls in the code behind. But now I'm having problems binding the generated controls with the ViewModel properties. My code is:
<UserControl x:Class="SVT.Teste.UserControl1"
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"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300"
DataContext="UserControl1ViewModel">
<Grid Name="GridContainer">
</Grid>
</UserControl>
and code behind:
public UserControl1()
{
InitializeComponent();
System.Windows.Controls.Button newBtn = new Button();
newBtn.SetBinding(Button.ContentProperty, new Binding("Test"));
GridContainer.Children.Add(newBtn);
}
public class UserControl1ViewModel
{
private string test = "ola";
public string Test
{
get { return test; }
}
}
When I run this I get:
"System.Windows.Data Error: 40 : BindingExpression path error: 'Test'
property not found on 'object' ''String' (HashCode=-946585093)'.
BindingExpression:Path=Test; DataItem='String' (HashCode=-946585093);
target element is 'Button' (Name=''); target property is 'Content'
(type 'Object')"
Can you help me?

Answer 1

You are setting DataContext property of UserControl1 to a string instead of your view model instance.
You need to do something like this:
<UserControl xmlns:local="clr-namespace:NAMESPACE_WHERE_VIEWMODEL_IS_DEFINED">
<UserControl.DataContext>
<local:UserControl1ViewModel />
</UserControl.DataContext>
<!-- unrelated code omitted -->
</UserControl>

Answer 2

You are setting you DataContext to the type, not an instance that has the properties.
In your method that creates the user control do :
public UserControl1()
{
InitializeComponent();
System.Windows.Controls.Button newBtn = new Button();
newBtn.SetBinding(Button.ContentProperty, new Binding("Test"));
GridContainer.Children.Add(newBtn);
**DataContext = new UserControl1ViewModel();**
}
You still have more work to do. The way you have it no notifications or update will happen. Implement the INotifyPropertyChanged interface (on UserControlViewModel). And remove setting DataContext in the XAML to the type.

Answer 3

try with this binding
Binding MyBinding = new Binding();
MyBinding.Path = new PropertyPath("Test");
newBtn.DataContext = new UserControl1ViewModel(); //or MyBinding.Source = new //UserControl1ViewModel();
newBtn.SetBinding(Button.ContentProperty, MyBinding);

Answer 4

max is right, but i have another question. why do you want create your usercontrol dynamic when you have a viemwodel you wanna bind to? makes no sense to me. let me explain:
if you have a viewmodel - you know in mind how this viewmodel should be rendered and what the bindings are. so you could create a usercontrol/view for this viewmodel
MyUserControl1View.xaml
<UserControl>
<Grid>
<Button Content="{Binding Test}"/>
<!-- more controls and binding if the viewmodel expose more-->
</Grid>
</UserControl>
so what you have now is a representation of your viewmodel. they are not connnected but your viewmodel should look like this and the binding are set. till now no datacontext is set at all.
all you have to do now is to go the viewmodel first approach and the use of datatemplates.
let us assume the following in your mainwindow
<Window>
<Window.Resources>
<DataTemplate Datatype="{x:Type local:Usercontrol1viewmodel}">
<view:MyUserControl1View/>
</DataTemplate>
</Window.Resources>
now wpf knows how to render Usercontrol1viewmodel.
one step more in your mainwindow viewmodel you handle your Usercontrol1viewmodel.
public Usercontrol1viewmodel MyWhatEver {get;set;}
if you bind this property to a contentpresenter, you will see the wpf magic;)
<ContentPresenter Content="{Binding MyWhatEver}"/>
now you see the MyUserControl1View in the contentpresenter, no dynamic view code needed. just go with your viewmodels.
ps: feel free to edit my bad english.