Errors in App.xaml trying to use MVVM Light in Windows Phone 8 project

Question

When I add the MVVM Light package via NuGet I get errors referencing the lines in the App.xaml file added during the install. These errors only appear in Windows Phone 8 projects. The exact same lines in a Windows Phone 7 project do not raise any errors. The MVVM Light added lines are:

<ResourceDictionary>
    <vm:ViewModelLocator x:Key="Locator" d:IsDataSource="True" />
     <ResourceDictionary.MergedDictionaries></ResourceDictionary.MergedDictionaries>
</ResourceDictionary>

These lines are positioned just before the ending </Application.Resources> tag. The errors reported in the Error List pane are:

• Each dictionary must have an associated key
• The name "ViewModelLocator" does not exist in the namespace "clr-namespace:sdkVoiceAlarmClockWP8CS.ViewModel"

This seems to make sense since the <ResourceDictionary> tag does not have a key attribute. However, if I try to move this block of lines outside the block, I get a whole new set of errors.

As far as the ViewModelLocator problem is concerned, I double-checked and the following namespace is added to the <Application> tag as an attribute and it is not flagged with any errors:

xmlns:vm="clr-namespace:sdkVoiceAlarmClockWP8CS.ViewModel" mc:Ignorable="d"

Why does this exact same set of lines work fine in a Windows Phone 7 project and how can I fix the namespace problems I am having in my Windows Phone 8 project?

Just in case this is due to a more complex problem here is the entire App.xaml file:

<?xml version="1.0" encoding="utf-8"?>
<!-- 
    Copyright (c) 2012 Microsoft Corporation.  All rights reserved.
    Use of this sample source code is subject to the terms of the Microsoft license 
    agreement under which you licensed this sample source code and is provided AS-IS.
    If you did not accept the terms of the license agreement, you are not authorized 
    to use this sample source code.  For the terms of the license, please see the 
    license agreement between you and Microsoft.

    To see all Code Samples for Windows Phone, visit http://go.microsoft.com/fwlink/?LinkID=219604
-->
<Application x:Class="AlarmClockWithVoice.App" 
             xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone" 
             xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone" 
             xmlns:toolkit="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone.Controls.Toolkit" 
             xmlns:telerikPrimitives="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Primitives" 
             xmlns:p1="http://schemas.microsoft.com/winfx/2006/xaml" 
             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:vm="clr-namespace:sdkVoiceAlarmClockWP8CS.ViewModel" mc:Ignorable="d"
             >

    <!--Application Resources-->
    <Application.Resources>
        <Style x:Key="TransitionPageStyle" TargetType="phone:PhoneApplicationPage">
            <Setter Property="toolkit:TransitionService.NavigationInTransition">
                <Setter.Value>
                    <toolkit:NavigationInTransition>
                        <toolkit:NavigationInTransition.Backward>
                            <toolkit:TurnstileTransition Mode="BackwardIn" />
                        </toolkit:NavigationInTransition.Backward>
                        <toolkit:NavigationInTransition.Forward>
                            <toolkit:TurnstileTransition Mode="ForwardIn" />
                        </toolkit:NavigationInTransition.Forward>
                    </toolkit:NavigationInTransition>
                </Setter.Value>
            </Setter>
            <Setter Property="toolkit:TransitionService.NavigationOutTransition">
                <Setter.Value>
                    <toolkit:NavigationOutTransition>
                        <toolkit:NavigationOutTransition.Backward>
                            <toolkit:TurnstileTransition Mode="BackwardOut" />
                        </toolkit:NavigationOutTransition.Backward>
                        <toolkit:NavigationOutTransition.Forward>
                            <toolkit:TurnstileTransition Mode="ForwardOut" />
                        </toolkit:NavigationOutTransition.Forward>
                    </toolkit:NavigationOutTransition>
                </Setter.Value>
            </Setter>
        </Style>
        <ResourceDictionary>
            <vm:ViewModelLocator x:Key="Locator" d:IsDataSource="True" />
            <ResourceDictionary.MergedDictionaries></ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>

    <Application.ApplicationLifetimeObjects>
        <!--Required object that handles lifetime events for the application-->
        <shell:PhoneApplicationService Launching="Application_Launching" Closing="Application_Closing" Activated="Application_Activated" Deactivated="Application_Deactivated" />
    </Application.ApplicationLifetimeObjects>

</Application>

Answer 1

I had this problem before. To make it work in WP8 replace this:

<ResourceDictionary>
    <vm:ViewModelLocator x:Key="Locator" d:IsDataSource="True" />
    <ResourceDictionary.MergedDictionaries></ResourceDictionary.MergedDictionaries>
</ResourceDictionary>

With just this:

<vm:ViewModelLocator x:Key="Locator" d:IsDataSource="True" />

But I haven't bothered as to why it works on WP7 but not WP8

Answer 2

Insert everything into ResourceDictionary rather than in ApplicationResources with all necessary namespaces, as mentioned already in this stackoverflow question.