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Create a simple wpf trigger for one object that affects another

This is the closest thing that I came to create a simple trigger. I just want the exponential IsMouseOver == true symbol to display the button. The problem is that Setter TargetName says: the TargetName property is not a valid target for "Setter" because an element named "ButtonExpand" was not found. Make sure the target is declared before any setters, triggers, or conditions that use it. What am I doing wrong?

<UserControl.Resources> <Style TargetType="DataGrid"> <Style.Triggers> <Trigger Property="IsMouseOver" Value="True"> <Setter TargetName="ButtonExpand" Property="Visibility" Value="Visible" /> </Trigger> </Style.Triggers> </Style> </UserControl.Resources> <Grid> <DataGrid Name="MainDataGrid" ItemsSource="{Binding Programs}" IsReadOnly="True" AutoGenerateColumns="false" > <DataGrid.Columns> <DataGridTextColumn Header="Name" Binding="{Binding Name}"/> <DataGridTextColumn Header="Version" Binding="{Binding Version}"/> <DataGridTextColumn Header="Publisher" Binding="{Binding Publisher}"/> </DataGrid.Columns> </DataGrid> <Button Name="ButtonExpand" Height="25" Width="25" HorizontalAlignment="Right" VerticalAlignment="Bottom" Visibility="Hidden">+</Button> </Grid>

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TargetName is not intended to be used in a style trigger collection. A style has no naming, so it makes no sense to designate elements by name. But the template (either DataTemplate or ControlTemplate) has a NameScope.

See this link.

You can do this with a DataTrigger for Button. Note that you must set the appearance of the style properties for the DataTrigger.

 <Grid Name="MainGrid"> <DataGrid ItemsSource="{Binding Programs}" IsReadOnly="True" AutoGenerateColumns="false" > <DataGrid.Columns> <DataGridTextColumn Header="Name" Binding="{Binding Name}"/> <DataGridTextColumn Header="Version" Binding="{Binding Version}"/> <DataGridTextColumn Header="Publisher" Binding="{Binding Publisher}"/> </DataGrid.Columns> </DataGrid> <Button Name="ButtonExpand" Height="25" Width="25" HorizontalAlignment="Right" VerticalAlignment="Bottom" Content="+"> <Button.Style> <Style TargetType="Button"> <Setter Property="Visibility" Value="Hidden"/> <Style.Triggers> <DataTrigger Binding="{Binding ElementName=MainGrid, Path=IsMouseOver}" Value="True"> <Setter Property="Visibility" Value="Visible" /> </DataTrigger> </Style.Triggers> </Style> </Button.Style> </Button> </Grid>

Another way to do this is to associate ButtonExpand's Visibilty with the IsMouseOver DataGrid property to the converter.

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 <Grid Name="MainGrid"> <DataGrid ItemsSource="{Binding Programs}" IsReadOnly="True" AutoGenerateColumns="false" > <DataGrid.Columns> <DataGridTextColumn Header="Name" Binding="{Binding Name}"/> <DataGridTextColumn Header="Version" Binding="{Binding Version}"/> <DataGridTextColumn Header="Publisher" Binding="{Binding Publisher}"/> </DataGrid.Columns> </DataGrid> <Button Name="ButtonExpand" Margin="0,0,20,20" Height="25" Width="25" HorizontalAlignment="Right" VerticalAlignment="Bottom" Content="+"> <Button.Style> <Style TargetType="Button"> <Setter Property="Visibility" Value="Hidden"/> <Style.Triggers> <DataTrigger Binding="{Binding ElementName=MainGrid, Path=IsMouseOver}" Value="True"> <Setter Property="Visibility" Value="Visible" /> </DataTrigger> </Style.Triggers> </Style> </Button.Style> </Button> </Grid>
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