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WPF MVVM - How can I pass two variables from the ViewModel associated with the first window to the second ViewModel associated with the second window?

I don't want to use Prism or MVVM Light solutions and would like to pass two parameters to the second window? How could I do that? I was looking for some information on this topic, but unfortunately most of them use packages...

try this:
App.xaml
<Application.Resources>
<vm:MainViewModel x:Key="YourViewModel" />
</Application.Resources>
MainWindow.xaml
<Window x:Class="ABC.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:ABC"
DataContext="{StaticResource YourViewModel}"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid>
<TextBlock Text="{Binding SomeVar}"/>
</Grid>
</Window>
SecondWindow.xaml
<Window x:Class="ABC.SecondWindow"
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:ABC"
DataContext="{StaticResource YourViewModel}"
mc:Ignorable="d"
Title="SecondWindow" Height="450" Width="800">
<Grid>
<TextBox Text="{Binding SomeVar}"/>
</Grid>
</Window>

I guess you could just send parameters in the constructor of the second window, wherever you are creating your window.
var newwin = new SecondWindow("second param is int", 42 );
newwin.Show();
And then just create an another constructor for your window:
public SecondWindow(string a, int b) : this()
{
var secondVM = (SecondViewModel)DataContext;
secondVM.IAmSendingYouTwoParams( a,b);
...
}

UserControl in windows phone 8.1 blank template

My requirement is masterpage in windows phone 8.1 blank template, i searched in the google, they suggest the usercontrol, i applied that scenario but not working,Below is my tried sample code.
`I'm try create Application where i required to use User Control.I'm already created MainPage.xaml here code below
`
<Page
x:Class="VtDesigning.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:VtDesigning"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Grid>
</Grid>
</Page>
and usercontrol defined below
<UserControl
x:Class="VtDesigning.MyUserControl2"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:VtDesigning"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
d:DesignHeight="300"
d:DesignWidth="400">
<Grid>
<StackPanel Height="50" Background="Chocolate">
<TextBlock Text="hi hellow how are you"
FontSize="25"
Margin="0,0,154,0"/>
</StackPanel>
</Grid>
</UserControl>
How to i call this usercontrol in MainPage.xaml.
Thanks,
Venky.

Set a reference to the location of the user control and add the user control to your layout as a normal control
<Page
x:Class="VtDesigning.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:VtDesigning"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:project="using:MyProject.UserControls"
mc:Ignorable="d"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Grid>
<project:MyUserControl/>
</Grid>

How to HardCode String in Xml in Silverlight

i am new to xml in silverlight.i have one small xml file below
<FlowActivities>
<SequenceFlow >
<FlowWriteLine>
hiiii
</FlowWriteLine>
</SequenceFlow>
</FlowActivities>
in this i want to hardcode some namespace in rootnode.like
<FlowActivities x:Class="WorkflowConsoleApplication1.modify"
xmlns="http://schemas.microsoft.com/netfx/2009/xaml/activities"
mc:Ignorable="sap2010"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
sap2010:ExpressionActivityEditor.ExpressionActivityEditor="C#"
xmlns:sap2010="http://schemas.microsoft.com/netfx/2010/xaml/activities/presentation"
xmlns:sco="clr-namespace:System.Collections.ObjectModel;assembly=mscorlib"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<SequenceFlow >
<FlowWriteLine>
hiiii
</FlowWriteLine>
</SequenceFlow>
</FlowActivities>
for getting this wht i have to do..? pls sort this out..?

XAML is not a current XML file, is a language based on XML. Therefore you can not write random, non-existent XML tags.
To hardcode a string in SL XAML file:
<UserControl
x:Class="Test_SL_HardcodeString.MainPage"
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:system="clr-namespace:System;assembly=mscorlib" mc:Ignorable="d"
d:DesignHeight="300"
d:DesignWidth="400">
<UserControl.Resources>
<system:String x:Key="myString">This is a test string</system:String>
</UserControl.Resources>
<Grid x:Name="LayoutRoot" Background="White">
<TextBox Text="{StaticResource myString}"/>
</Grid>
</UserControl>

You can't. You have to set the variable like JoanComasFdz said.
If you must use the same format, you can create a separate class(viewmodel) for eg. MyXMLData.cs to read and parse xml file. Read the XML node and set the class variable "theString" from this class. In XAML, you can create an instance of the class in the resources section and set the data context of the Grid or the textbox to that object.
<UserControl
x:Class="Test_SL_HardcodeString.MainPage"
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:system="clr-namespace:System;assembly=mscorlib" mc:Ignorable="d"
xmlns:viewmodel="clr-namespace:MyNameSpace.ViewModels"
d:DesignHeight="300"
d:DesignWidth="400">
<UserControl.Resources>
<viewmodel:MyXMLData x:key="myxmldataclass"/>
</UserControl.Resources>
<Grid x:Name="LayoutRoot" Background="White" DataContext="{StaticResource myxmldataclass}" >
<TextBox Text="{StaticResource theString}"/>
</Grid>
</UserControl>

WPF: How to communicate two usercontrols correctly, using MVVM?

I'm developing an WPF (C#) application using MVVM. I've created a new project which is a simplification that focuses only on the problem I have.
In the View there is a Panel which is composed by a PanelButton which consists on two buttons and PanelDisplay.
The idea is that when orange button is pressed the PanelDisplay should change its color to orange and when green button is pressed PanelDisplay should change to green.
Code for Panel:
<UserControl x:Class="WpfApplication1.View.Panel"
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:view="clr-namespace:WpfApplication1.View"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="600">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="0.3*"/>
<ColumnDefinition Width="0.7*"/>
</Grid.ColumnDefinitions>
<view:PanelButtons Grid.Column="0"></view:PanelButtons>
<view:PanelDisplay Grid.Column="1"></view:PanelDisplay>
</Grid>
</UserControl>
The code for PanelButtons.xaml:
<UserControl x:Class="WpfApplication1.View.PanelButtons"
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:viewModel="clr-namespace:WpfApplication1.ViewModel"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<UserControl.Resources>
<viewModel:PanelButtonsAndDisplayVM x:Key="panelButtonsAndDisplayVM"/>
</UserControl.Resources>
<Grid Background="LightGray">
<StackPanel>
<Button Width="64" Height="64"
Command="{Binding Source={StaticResource panelButtonsAndDisplayVM}, Path=PressedOrange}">Orange</Button>
<Button Width="64" Height="64"
Command="{Binding Source={StaticResource panelButtonsAndDisplayVM}, Path=PressedGreen}">Green</Button>
</StackPanel>
</Grid>
The code for PanelDisplay.xaml:
<UserControl x:Class="WpfApplication1.View.PanelDisplay"
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:viewModel="clr-namespace:WpfApplication1.ViewModel"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<UserControl.Resources>
<viewModel:PanelButtonsAndDisplayVM x:Key="panelButtonsAndDisplayVM"/>
</UserControl.Resources>
<Grid Background="{Binding Source={StaticResource panelButtonsAndDisplayVM},Path=Color}" >
</Grid>
The problem is that PanelDisplay does not change its color, to solve this I made a singleton class that launched an event and subscribed PanelDisplay to that event and it worked, but I need two "Panels" in the MainWindow, so if I use this solution the two panels will change their color because they'll both get the same event and only one PanelDisplay should be updated.
Code for the MainWindow:
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:view="clr-namespace:WpfApplication1.View"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="0.5*"/>
<RowDefinition Height="0.5*"/>
</Grid.RowDefinitions>
<view:Panel Grid.Row="0"/>
<view:Panel Grid.Row="1"/>
</Grid>
So, how can be actualized each PanelDisplay separately? Any ideas?

Your PanelButtons.xaml and PanelDisplay.xaml do not use the same instance of PanelButtonsAndDisplayVM class because each is declaring their own instance in resources.
Instead, declare PanelButtonsAndDisplayVM instance in Panel.xaml as DataContext so it is propagated to all descendant controls:
<UserControl x:Class="WpfApplication1.View.Panel"
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:view="clr-namespace:WpfApplication1.View"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="600">
<UserControl.DataContext>
<view:PanelButtonsAndDisplayVM/>
</UserControl.DataContext>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="0.3*"/>
<ColumnDefinition Width="0.7*"/>
</Grid.ColumnDefinitions>
<view:PanelButtons Grid.Column="0"></view:PanelButtons>
<view:PanelDisplay Grid.Column="1"></view:PanelDisplay>
</Grid>
</UserControl>
And use it in PanelButtons.xaml like this:
<UserControl x:Class="WpfApplication1.View.PanelButtons"
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:viewModel="clr-namespace:WpfApplication1.ViewModel"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<Grid Background="LightGray">
<StackPanel>
<Button Width="64" Height="64"
Command="{Binding PressedOrange}">Orange</Button>
<Button Width="64" Height="64"
Command="{Binding PressedGreen}">Green</Button>
</StackPanel>
</Grid>
</UserControl>
And in PanelDisplay.xaml like this:
<UserControl x:Class="WpfApplication1.View.PanelDisplay"
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:viewModel="clr-namespace:WpfApplication1.ViewModel"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<Grid Background="{Binding Path=Color}">
</Grid>
</UserControl>

You should create a separate viewmodel for each UserControl. For example you could have a PanelViewModel then as properties on that a PanelDisplayViewModel and a PanelButtonsViewModel.
A button is pressed on the PanelButtonsViewModel.
That method makes a call up to PanelViewModel to report the event.
The panel then updates the display by calling a method on the PanelDisplayViewModel.
Avoid the static resources for view models here and just use the standard DataContext on each user control and it should work out.

How can I define control as a resource and then place it onto form?

I want to do something like this:
<Window x:Class="WpfApplication10.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<Button x:Key="butt" Content="Yeah!" />
</Window.Resources>
<Grid>
<!-- Place button here -->
</Grid>
</Window>
How to do it? I want to create library of small user controls in single file.

<Grid>
<StaticResource ResourceKey="butt"/>
</Grid>
Should work...