Set property of ViewModel using setter within some Trigger - wpf

Question

I tried to google but all problems had related heading but problem context different. My problem is that I have a DataTrigger which gets triggered when certain property has a certain value i-e IsDockPanelVisible has true/false (different triggers for each value) in my case. Now when it gets triggered, it should set the value of Width - a property defined in ViewModel. Here is my specific code:
<Style.Triggers>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="False">
<Setter Property="mainWindowViewModel.Width" Value="Auto">
</Setter>
</DataTrigger>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="True">
<Setter Property="mainWindowViewModel.Width" Value="7*"></Setter>
<Setter Property="MinWidth">
<Setter.Value>
<MultiBinding Converter="{StaticResource StringSumtoIntConvert}">
<Binding ElementName="cdLblNotificationsHeader" Path="MinWidth"/>
<Binding ElementName="cdBtnNotificationsClose" Path="ActualWidth"/>
</MultiBinding>
</Setter.Value>
</Setter>
</DataTrigger>
</Style.Triggers>
Here is complete code:
<Window x:Class="EmbroidaryManagementSystem_V2._0.View.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:EmbroidaryManagementSystem_V2._0.View"
xmlns:adf="clr-namespace:EmbroidaryManagementSystem_V2"
xmlns:collectionVM="clr-namespace:EmbroidaryManagementSystem_V2._0.ViewModel.CollectionsViewModel"
xmlns:helperClasses="clr-namespace:EmbroidaryManagementSystem_V2._0.HelperClasses"
xmlns:mainWindowVM="clr-namespace:EmbroidaryManagementSystem_V2._0.ViewModel.UIViewModel"
mc:Ignorable="d"
Title="Khalil Embroidery Management System" Height="655.512" Width="1135.159" FontSize="24"
WindowStartupLocation="CenterScreen" MinWidth="200" MinHeight="300"
Icon="/EmbroidaryManagementSystem V2.0;component/Images/KhalilEmbroideryLogonobackgrnd2.png"
>
<Window.DataContext>
<!--<collectionVM:ClientCollectionVM/>-->
<mainWindowVM:MainWindowViewModel/>
</Window.DataContext>
<Window.Resources>
<helperClasses:StringSumtoIntConverter x:Key="StringSumtoIntConvert"/>
<ControlTemplate x:Key="DockedPanelButtonTemplate" TargetType="{x:Type Button}">
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Background" Value="Black"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
<Style x:Key="DockedPanelButton" TargetType="Button">
<Setter Property="LayoutTransform">
<Setter.Value>
<RotateTransform Angle="90"/>
</Setter.Value>
</Setter>
<!--<Setter Property="Template" Value="{StaticResource DockedPanelButtonTemplate}"/>-->
<Setter x:Name="border" Property="BorderBrush" Value="DodgerBlue"/>
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="BorderBrush" Value="Aquamarine"/>
<Setter Property="Background" Value="Yellow"/>
</Trigger>
</Style.Triggers>
</Style>
<!--<mainWindowVM:MainWindowViewModel x:Key="WindowViewModel"/>-->
<Style x:Key="OnIsDockPanelVisibleChangedGridBehaviour" TargetType="Grid">
<Style.Triggers>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="False">
<Setter Property="Visibility" Value="Collapsed"/>
</DataTrigger>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="True">
<Setter Property="Visibility" Value="Visible"/>
</DataTrigger>
</Style.Triggers>
</Style>
<Style x:Key="OnIsDockPanelVisibleChangedPanelColumnBehaviour" TargetType="ColumnDefinition">
<Style.Triggers>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="False">
<Setter Property="mainWindowViewModel.Width" Value="Auto">
</Setter>
</DataTrigger>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="True">
<Setter Property="mainWindowViewModel.Width" Value="7*"></Setter>
<Setter Property="MinWidth">
<Setter.Value>
<MultiBinding Converter="{StaticResource StringSumtoIntConvert}">
<Binding ElementName="cdLblNotificationsHeader" Path="MinWidth"/>
<Binding ElementName="cdBtnNotificationsClose" Path="ActualWidth"/>
</MultiBinding>
</Setter.Value>
</Setter>
</DataTrigger>
</Style.Triggers>
</Style>
<Style x:Key="OnIsDockPanelVisibleChangedButtonBehaviour" TargetType="Button"
BasedOn="{StaticResource DockedPanelButton}">
<Style.Triggers>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="True">
<Setter Property="Visibility" Value="Collapsed"/>
</DataTrigger>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="False">
<Setter Property="Visibility" Value="Visible"/>
</DataTrigger>
</Style.Triggers>
</Style>
<Style x:Key="OnIsDockPanelVisibleChangedGridSplitterBehaviour" TargetType="GridSplitter">
<Style.Triggers>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="True">
<Setter Property="Visibility" Value="Visible"/>
</DataTrigger>
<DataTrigger Binding="{Binding IsDockPanelVisible}" Value="False">
<Setter Property="Visibility" Value="Collapsed"/>
</DataTrigger>
</Style.Triggers>
</Style>
<SolidColorBrush x:Key="TransparentBackground">
Transparent
</SolidColorBrush>
<Style x:Key="LeftDockedPanelButton" TargetType="Button" BasedOn="{StaticResource OnIsDockPanelVisibleChangedButtonBehaviour}">
<Setter Property="BorderThickness" Value="0,0,0,15"/>
</Style>
<Style x:Key="RightDockedPanelButton" TargetType="Button" BasedOn="{StaticResource OnIsDockPanelVisibleChangedButtonBehaviour}">
<Setter Property="BorderThickness" Value="0,8,0,0"/>
</Style>
<BitmapImage x:Key="LogoImage" UriSource="/Images/KhalilEmbroideryLogonobackgrnd2.png"/>
</Window.Resources>
<!--<ScrollViewer HorizontalScrollBarVisibility="Auto">-->
<Grid x:Name="mainGrid" Background="#FFD6DBE9">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition MinHeight="103"/>
</Grid.RowDefinitions>
<Menu Height="18" VerticalAlignment="Top" Grid.Row="0" Margin="0,0,0,0">
<MenuItem Header="_Exit">
<MenuItem Header="Exit"/>
</MenuItem>
<MenuItem Header="_View">
<MenuItem Header="Notifications" Command="{Binding ShowDockPanelCommand}"/>
</MenuItem>
<MenuItem Header="Add _New">
<MenuItem Header="Employee"/>
<MenuItem Header="Employee Salary"/>
</MenuItem>
<MenuItem Header="_About">
<MenuItem Header="About us"/>
</MenuItem>
</Menu>
<ScrollViewer HorizontalScrollBarVisibility="Auto" Grid.Row="1">
<Grid x:Name="innerContentGrid" MinHeight="500" MinWidth="600">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="20*" MinWidth="{Binding MinWidth, ElementName=tabDataEntities}"/>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Style="{StaticResource OnIsDockPanelVisibleChangedPanelColumnBehaviour}" Width="{Binding }"/>
</Grid.ColumnDefinitions>
<GridSplitter x:Name="gridSplitter" Grid.Column="1" HorizontalAlignment="Center"
Width="3" Margin="0,10,0,0" Background="#FF657695"
Style="{StaticResource OnIsDockPanelVisibleChangedGridSplitterBehaviour}"/>
<Grid x:Name="gridNotificationsHeader" Grid.Column="2" Background="#FF657695" Margin="0,10,0,0"
Height="30" VerticalAlignment="Top" Style="{StaticResource OnIsDockPanelVisibleChangedGridBehaviour}">
<Grid.ColumnDefinitions>
<ColumnDefinition x:Name="cdLblNotificationsHeader"
MinWidth="{Binding Width, ElementName=lblNotificationsHeader}"/>
<ColumnDefinition x:Name="cdBtnNotificationsClose" Width="Auto"/>
</Grid.ColumnDefinitions>
<Label x:Name="lblNotificationsHeader" Content="Notifications" VerticalAlignment="Top"
FontSize="14.667" Height="29" Foreground="#FFEBF0EE" HorizontalAlignment="Left" Width="92"/>
<Button x:Name="btnNotificationsClose" Content="X"
Margin="0,5,8,0" VerticalAlignment="Top" Width="20" FontFamily="Verdana" HorizontalAlignment="Right"
Background="Transparent" FontSize="13.333" Foreground="Black" Grid.Column="1"
Command="{Binding HideDockPanelCommand}"/>
</Grid>
<TabControl Grid.Column="0" x:Name="tabDataEntities" Margin="0,10,5,0" FontSize="12"
MinWidth="{Binding ElementName=TabItemOne, Path=ActualWidth}">
<TabItem x:Name="TabItemOne">
<TabItem.Header>Tab Item</TabItem.Header>
<Grid Background="#FFE5E5E5" Margin="0,0,0,0"/>
</TabItem>
<TabItem Header="TabItem">
<Grid Background="#FFE5E5E5"/>
</TabItem>
</TabControl>
<Button x:Name="btnShowNotificationsPanel" Content="Notifications" Grid.Column="2"
Margin="0,12,-0,0" VerticalAlignment="Top" Style="{StaticResource RightDockedPanelButton}" Background="Transparent"
FontSize="12" Height="Auto" HorizontalAlignment="Right" Width="Auto"
Command="{Binding ShowDockPanelCommand}"/>
</Grid>
</ScrollViewer>
</Grid>
Width is property in my ViewModel and not FrameworkElement.Width. However, it has the same double type. ViewModel class is MainWindowViewModel and its object in XAML is mainWindowVM.

Answer 1

You can not set view model properties with a setter of your view.
Have a look here: Setter.Property Property.
It states that you can only uses a DependencyProperty as the value for the setter (Besides, you cannot specify a binding expression there, just a string value).
<object Property="DependencyProperty" .../>
Suggestion:
If IsDockPanelVisible is a property inside your view model, you could react to change events there in your view model, either by subscribing to INotifyPropertyChanged of this property or by calling a method in the setter of IsDockPanelVisible.
You could then set another property in your view model which is bound to the view and then achieve your desired result.