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Combobox showing error "Binding expression path error"

I have two combobox which are currently binded to the user model. The first combobox supposed to show the current userRole value before clicking on the combobox. The other combobox supposed to show the userStatus either 1 or 0. Now the second combobox is not displaying any value. However the first combobox is displaying the value once its clicked only.
Here is the xaml code:
<StackPanel Orientation="Horizontal">
<TextBlock FontSize="12" Text="User Role: " VerticalAlignment="Center" />
<ComboBox x:Name="cbUserRole" FlowDirection="LeftToRight" FontSize="16" Foreground="MidnightBlue" HorizontalAlignment="Stretch" VerticalAlignment="Center" Loaded="cbUserRole_Loaded" SelectedItem="{Binding UserRole, Mode=TwoWay" />
</StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock FontSize="12" Text="User Status: " VerticalAlignment="Center" />
<ComboBox x:Name="cbUserStatus" FlowDirection="LeftToRight" FontSize="16" Foreground="MidnightBlue" HorizontalAlignment="Stretch" VerticalAlignment="Center" SelectedIndex="{Binding UserStatus, Converter={StaticResource boolToIndexConverter}}" />
</StackPanel>
Here is my converter code:
public class BoolToIndexConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return ((bool)value == true) ? 0 : 1;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return ((int)value == 0) ? true : false;
}
}
The code above is refered from this link:
Here is my User model code:
private string userrole;
public string UserRole
{
get { return userrole; }
set
{
userrole = value;
OnPropertyChanged("UserRole");
}
}
private bool userstatus;
public bool UserStatus
{
get { return userstatus; }
set
{
userstatus = value;
OnPropertyChanged("UserStatus");
}
}
How can i fix this problems? I did search and tried from different blogs but its not working for me.

The problem is that your combobox's DataContext is User, but you need to set ItemsSource from DataGrid's datacontext. In order to do that you need to use the following syntax:
<ComboBox
ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor,AncestorType={x:Type DataGrid}}, Path=DataContext.Users}"
x:Name="cbUserRole" FlowDirection="LeftToRight" FontSize="16" Foreground="MidnightBlue" HorizontalAlignment="Stretch" VerticalAlignment="Center"
SelectedItem="{Binding UserRole,Mode=TwoWay}"></ComboBox>
And Remove Loaded handler.
You can also use <DataGrid DataContext="{StaticResource uvm}" instead of codebehind code:
var userList = new UserViewModel().Users;
userDataGrid.ItemsSource = userList;
You don't have ItemsSource for your Status Combobox. I think you should add collection of statuses to UserViewModel and bind it like in the example above.

Data binding a button visibility in WPF isn't working

Alot of code incoming, Some of this might be useless because i was trying alot of things to get this working.
I am trying to make the button Export Installer invisible unless the selected installer has a value of TRUE on IsDownloaded
so i'll start with my WPF
DataContext="{Binding Source={StaticResource TheViewModel}}"
Title="MainWindow" Height="458" Width="755">
<Window.Resources>
<ViewModel:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter" />
<ViewModel:InstallerColorConverter x:Key="InstallerColorConverter" />
</Window.Resources>
<ListBox Height="300" Grid.Column="0" Grid.Row="0" SelectionMode="Single" ItemsSource="{Binding SelectedProduct.Installers}" SelectedItem="{Binding SelectedInstaller}" >
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<Ellipse HorizontalAlignment="Right" Fill="{Binding InstallerRelativeToCurrent, Converter={StaticResource InstallerColorConverter}}" Margin="5,5,5,5 " Height="20" Width="20" Stroke="Black"></Ellipse>
<TextBlock Margin="5,0,5,0" Text="{Binding Name}" />
<TextBlock Text=" " />
<TextBlock Text="{Binding VersionNumber}" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<StackPanel Grid.Column="0" Grid.Row="1" Orientation="Horizontal" HorizontalAlignment="Stretch">
<Button Name="btnInstall" Margin="5,5,5,5" Height="50" Width="75" MouseDoubleClick="btnDownloadInstaller_MouseDoubleClick" >Download</Button>
<Button Name="btnExportInstaller" Visibility="{Binding Path=SelectedInstaller.IsDownloaded, RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type Button}}, Converter={StaticResource BoolToVisibilityConverter}}" Margin="5,5,5,5" Height="50" Width="90" MouseDoubleClick="btnExportInstaller_MouseDoubleClick" >Export Installer</Button>
</StackPanel>
The main things to point out in that is
<Button Name="btnExportInstaller" Visibility="{Binding Path=SelectedInstaller.IsDownloaded, RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type Button}}, Converter={StaticResource BoolToVisibilityConverter}}" Margin="5,5,5,5" Height="50" Width="90" MouseDoubleClick="btnExportInstaller_MouseDoubleClick" >Export Installer</Button>
and
<ViewModel:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter" />
now in my class BoolToVisibilityConver
public class BoolToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
var booool = (bool)value;
if (booool)
return Visibility.Collapsed;
else
return Visibility.Visible;
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
// Do the conversion from visibility to bool
return Visibility.Collapsed;
}
}
Then finally in the view model i have
private Visibility _IsVisible;
public Visibility IsVisible
{
get { return _IsVisible; }
set { _IsVisible = value; OnPropertyChanged(nameof(_SelectedInstaller.IsDownloaded)); }
}
private Products _SelectedProduct;
public Products SelectedProduct
{
get { return _SelectedProduct; }
set { _SelectedProduct = value; OnPropertyChanged(nameof(SelectedProduct)); }
private Installers _SelectedInstaller;
public Installers SelectedInstaller
{
get { return _SelectedInstaller; }
set { _SelectedInstaller = value; OnPropertyChanged(nameof(SelectedInstaller)); }
It doesn't work
I'm getting these 2 errors on the console and i don't understand them
System.Windows.Data Error: 1 : Cannot create default converter to perform 'one-way' conversions between types 'System.Boolean' and 'System.Windows.Visibility'. Consider using Converter property of Binding. BindingExpression:Path=SelectedProduct.IsInstalled; DataItem='ViewModel' (HashCode=26987408); target element is 'Grid' (Name=''); target property is 'Visibility' (type 'Visibility')
System.Windows.Data Error: 5 : Value produced by BindingExpression is not valid for target property.; Value='False' BindingExpression:Path=SelectedProduct.IsInstalled; DataItem='ViewModel' (HashCode=26987408); target element is 'Grid' (Name=''); target property is 'Visibility' (type 'Visibility')
If anyone can point out what i'm doing wrong here i would love you forever!

SOLVED..this is the working code
<Window.Resources>
<ViewModel:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter" />
<Button Name="btnExportInstaller" Visibility="{Binding SelectedInstaller.IsDownloaded , Converter={StaticResource BoolToVisibilityConverter}}" Margin="5,5,5,5" Height="50" Width="90" MouseDoubleClick="btnExportInstaller_MouseDoubleClick">Export Installer</Button>
public class BoolToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, CultureInfo culture)
{
var booool = (bool)value;
if (booool == false)
return Visibility.Collapsed;
else
return Visibility.Visible;
}
public object ConvertBack(object value, Type targetType,
object parameter, CultureInfo culture)
{
if (value is Visibility && (Visibility)value == Visibility.Visible)
{
return true;
}
return false;
}
}
Inside viewmodel
private Installers _SelectedInstaller;
public Installers SelectedInstaller
{
get { return _SelectedInstaller; }
set { _SelectedInstaller = value; OnPropertyChanged(nameof(SelectedInstaller)); }
private Visibility _IsVisible;
public Visibility IsVisible
{
get { return _IsVisible; }
set { _IsVisible = value; OnPropertyChanged(nameof(SelectedInstaller.IsDownloaded)); }
}

Using a IConverter to deal with {NewItemPlaceholder} in WPF / XAML / MVVM

Here is my DataTemplate:
<UserControl.Resources>
<converter:PlaceholderConverter x:Key="_placeholderConverter"/>
<!-- Data(Display)Template for data objects of x:Type Customer-->
<DataTemplate DataType="{x:Type model:Customer}">
<!-- Customer Properties will be vertically stacked -->
<ContentControl >
<StackPanel>
<TextBlock Text="{Binding FirstName}"/>
<TextBlock Text="{Binding LastName}"/>
<TextBlock Text="{Binding Phone}"/>
</StackPanel>
</ContentControl>
</DataTemplate>
<UserControl.Resources>
And the two different 'container's:
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="25"/>
<RowDefinition Height="100"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Button Grid.Row="0"
Content="Delete"
HorizontalAlignment="Left"
VerticalAlignment="Top"
Width="75"
Command="{Binding DeleteCommand}"/>
<DataGrid Grid.Row="1"
ItemsSource="{Binding Customers}"
SelectedItem="{Binding SelectedCustomer}"
AutoGenerateColumns="True"/>
<ListBox
Grid.Row="2"
ItemsSource="{Binding Customers, Mode=OneWay}"/>
</Grid>
And the app:
How to remove the {NewItemPlaceholder}? [Done, solution below].
How to prevent the binding error that mention "{NewItemPlaceholder}" when clicking in one of the empty rows in the table above intending on adding a new row (I can still add rows).
The errors:
...Cannot convert '{NewItemPlaceholder}' from type 'NamedObject' to type 'CustomerExample.Model.Customer'...
...ConvertBack cannot convert value '{NewItemPlaceholder}' (type 'NamedObject'). BindingExpression:Path=SelectedCustomer; DataItem='CustomerViewModel'...
I can write an IConverter implementation, but how to tie it in to the XAML?
thanks in advance :-)
Here is the implementation of the IConverter:
public class PlaceholderConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value != null && value.ToString() == "{NewItemPlaceholder}")
return DependencyProperty.UnsetValue;
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
and to bind to individual items, the XAML goes something like:
<TextBlock Text="{Binding Name, Converter={StaticResource PlaceholderConverter}}"/>
But I think I need to add it 'globally' to the data collection elements, not to where individual properties are being bound.

You don't need a Binding Converter. Instead, bind the ListBox to a CollectionViewSource that wraps the Custumers collection. The CollectionViewSource skips the NewItemPlaceholder element from the source collection.
<UserControl.Resources>
...
<CollectionViewSource x:Key="CustomersCVS" Source="{Binding Customers}"/>
</UserControl.Resources>
...
<ListBox ItemsSource="{Binding Source={StaticResource CustomersCVS}}"/>
You also don't need a Converter for the SelectedItem Binding. Just set the Binding's TargetNullValue property:
<DataGrid SelectedItem="{Binding SelectedCustomer,
TargetNullValue={x:Static CollectionView.NewItemPlaceholder}}" .../>

Even though the accepted answer is correct for the OP's question I needed a more general approach to prevent the error and still allow users to add rows. As I used this ValueConverter for many different object types I used reflection to determine the target type's constructor and just returned a new object of that type.
public class IgnoreNewItemPlaceHolderConverter : IValueConverter
{
private const string NewItemPlaceholderName = "{NewItemPlaceholder}";
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == DependencyProperty.UnsetValue)
return DependencyProperty.UnsetValue;
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value != null && value.ToString() == NewItemPlaceholderName)
{
var ctors = targetType.GetConstructors();
// invoke the first public constructor with no parameters.
return ctors[0].Invoke(new object[] { });
}
return value;
}
}

Using ObjectDataProvider inside HierarchicalDataTemplate

I want to add items of my class treeviewitem to a TreeView.
And I want to bind the ItemSource of this TreeViewItem to a method of itself !
I am trying to use the ObjectDataProvider for this.. See my XAML:
<Grid Background="#FFE5E5E5">
<Grid.Resources>
<HierarchicalDataTemplate DataType="{x:Type myNs:treeviewitem}">
<HierarchicalDataTemplate.Resources>
<ObjectDataProvider x:Key="getItems"
MethodName="GetItems"
ObjectInstance="{Binding RelativeSource={RelativeSource Self}}" />
</HierarchicalDataTemplate.Resources>
<HierarchicalDataTemplate.ItemsSource>
<Binding Source="{StaticResource getItems}" />
</HierarchicalDataTemplate.ItemsSource>
<StackPanel Orientation="Horizontal">
<TextBlock Margin="5,0,0,0"
Text="{Binding Name}" />
</StackPanel>
</HierarchicalDataTemplate>
</Grid.Resources>
<TreeView x:Name="guiTreeview"
HorizontalAlignment="Left"
Width="200" />
</Grid>
But binding to an ObjectInstance isnt possible!
How is it possible to get the current object instance "into" the ObjectDataProvider?
What would be the right way of doint this?
And NO, its not possible to use a Property ..

I have done it now with a ValueConverter.
XAML:
<Grid Background="#FFE5E5E5">
<Grid.Resources>
<HierarchicalDataTemplate DataType="{x:Type myNs:MyItem}" ItemsSource="{Binding RelativeSource={RelativeSource Self}, Converter={myNs:GetItemsConverter}}" >
<StackPanel Orientation="Horizontal">
<TextBlock Margin="5,0,0,0" Text="{Binding Name}" />
</StackPanel>
</HierarchicalDataTemplate>
</Grid.Resources>
<TreeView x:Name="guiTreeview" HorizontalAlignment="Left" Width="200" />
</Grid>
Converter:
public abstract class BaseConverter : MarkupExtension
{
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
}
public class GetItemsConverter : BaseConverter, IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var tvi = value as TreeViewItem;
if (tvi == null) return null;
var myitem = tvi.DataContext as MyItem;
if (myitem == null) return null;
return myitem.GetItems();
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return null;
}
}

WPF binding from parent to child element

Here is my XAML
<ListView x:Name="missingVariablesListView" ScrollViewer.CanContentScroll="True" HorizontalAlignment="Left" Height="320" Margin="81,28,0,0" VerticalAlignment="Top" Width="641" ItemsSource="{Binding}">
<ListView.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Vertical">
<StackPanel Orientation="Horizontal">
<TextBlock Text="ComponentID: " FontWeight="Bold" Foreground="Brown" />
<TextBlock Text="{Binding Name}"/>
</StackPanel>
<ItemsControl ItemsSource="{Binding Parameters}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="Variable Name: " Foreground="Green"/>
<TextBlock Text="{Binding Name}"/>
<TextBlock Text=" "/>
<TextBlock Text="Variable Value: " Foreground="Blue"/>
<TextBlock Text="{Binding Value}"/>
</StackPanel>
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
<ItemsControl.ItemContainerStyle>
<Style >
<Style.Triggers>
<DataTrigger Binding="{Binding IsMissing}" Value="false">
<Setter Property="UIElement.Visibility" Value="Collapsed"/>
</DataTrigger>
</Style.Triggers>
</Style>
</ItemsControl.ItemContainerStyle>
</ItemsControl>
<TextBlock Text="-----------------------------------------------------------------"/>
</StackPanel>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
Here is the CodeBehind
this.missingVariablesListView.DataContext = //Code to fill in the list View
Classes Involved
public class Component
{
private ObservableCollection<ComponentParameter> parameters = new ObservableCollection<ComponentParameter>();
public string Name
{
get;
set;
}
public ObservableCollection<ComponentParameter> Parameters
{
get{return parameters;}
set{parameters = value;}
}
}
public class ComponentParameter
{
public string Name
{
get;set;
}
public string Value
{
get;set;
}
public bool HasErrors
{
get;
set;
}
public bool IsMissing
{
get;set;
}
Sample Output (at the moment)
ComponentID: Component1
--------------------------
ComponentID: Component2
VariableName:Var1 Variable Value:Val1
VariableName:Var2 Variable Value:Val2
-----------------------
ComponentID: Component3
-----------------------
ComponentID: Component4
-----------------------
What i want to do is that whenever the boolean IsMissing is true for the inner element within the itemsControl i want to make sure that the ComponentID and the Name properties within the StackPanel (that has the orientation as horizontal) are not shown in the window including the child elements. Basically i am trying to find a way to exclude the whole description for that particular ComponentID whose isMissing variable is set to true. Any suggestions on this?

I would consider to add a property IsAnyParameterMissing to the Component class:
public class Component
{
private ObservableCollection<ComponentParameter> parameters = new ObservableCollection<ComponentParameter>();
public string Name
{
get;
set;
}
public ObservableCollection<ComponentParameter> Parameters
{
get{return parameters;}
set{parameters = value;}
}
public bool IsAnyParameterMissing
{
get { return this.Parameters.Any(param => param.IsMissing); }
}
}
And then bind the visibility to this property:
<StackPanel Orientation="Horizontal" Visibility="{Binding IsAnyParameterMissing, Converter={BooleanToVisibilityConverter}}">
<TextBlock Text="ComponentID: " FontWeight="Bold" Foreground="Brown" />
<TextBlock Text="{Binding Name}"/>
</StackPanel>
This will only display the StackPanel if any of the Parameters in the collection has its IsMissing property equal to true. Note that this will not change the visibility if the IsMissing property is changed for any of the items! This would need some additional work.
EDIT: Note that the {BooleanToVisibilityConverter} might need to be adjusted, depending on your available converters. Should be a simple task though.

One thing i noticed is that you don't implement the properties (such as "isMissing") as DependencyProperty. Neither do you use property change notifications via INotifyPropertyChanged.
You have to implement either of the two, otherwise changes of the properties will not be propagated through the bindings. That means, the trigger wouldn't trigger...

You could use a BooleanToVisibilityConverter to hide those items for you, although you may need to change your property or add a new IsPresent property for this:
In Resources:
<Converters:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter"
IsInverted="True" />
In your ListView.ItemTemplate:
<StackPanel Orientation="Horizontal" Visibility="{Binding IsMissing, Converter={
StaticResource BoolToVisibilityConverter}}">
<TextBlock Text="ComponentID: " FontWeight="Bold" Foreground="Brown" />
<TextBlock Text="{Binding Name}"/>
</StackPanel>
Custom BoolToVisibilityConverter with IsInverted property:
[ValueConversion(typeof(bool), typeof(Visibility))]
public class BoolToVisibilityConverter : IValueConverter
{
public bool IsInverted { get; set; }
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null || value.GetType() != typeof(bool)) return null;
bool boolValue = IsInverted ? !(bool)value : (bool)value;
return boolValue ? Visibility.Visible : Visibility.Collapsed;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null || value.GetType() != typeof(Visibility)) return null;
if (IsInverted) return (Visibility)value != Visibility.Visible;
return (Visibility)value == Visibility.Visible;
}
}
Now it will just take you one minute to implement it. I have updated the XAML example above to use it.