Eu tenho um controle de árvore que exibe um desempenho muito ruim e estou tentando rastrear a origem do problema.

Eu estou tentando descobrir se os avisos, como os seguintes, são importantes:

System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=ContextMenu.IsOpen; DataItem=null; target element is 'MultipleSelectionTreeViewItem' (Name=''); target property is 'NoTarget' (type 'Object')

O desempenho de atualizar o conteúdo da árvore mesmo com todos esses diags desligados é realmente terrível (mais de um segundo para preencher novamente ~ 300 itens), que é o que me fez olhar a saída do rastreamento.

Esses avisos são expelidos pela dúzia para cada clique na minha visualização em árvore e quando eu alterno a árvore para exibir diferentes conteúdos, várias centenas desses avisos ocorrem. No entanto, o conteúdo da árvore sempre aparece corretamente exibido, portanto, o contexto de dados deve estar definido como nulo apenas de forma transitória.

Eu coloquei uma ligação explícita paraDataContext com um conversor de valor para tentar ver o que está acontecendo.

<HierarchicalDataTemplate x:Key="HierarchyItemTemplate"
                          DataType="{x:Type local:HierarchyItem}"
                          ItemsSource="{Binding Children}">
    <StackPanel DataContext="{Binding Converter={StaticResource DbgConverter}}" Orientation="Horizontal">
       ...
    </StackPanel>
</HierarchicalDataTemplate>

... mas o valor nunca parece ser igual a nulo chegando lá.

Eu poderia definir um valor de fallback para todas as ligações para se livrar desses avisos, mas isso coloca muita confusão desnecessária no xaml e parece que está escondendo o problema em vez de resolvê-lo (supondo que seja mesmo um problema!).

Então minha pergunta é:

Esses diags podem causar o problema de desempenho?Em caso afirmativo, fornecer valores de fallback fará alguma diferença no desempenho quando os diags estiverem desativados?Se assim for, há uma maneira melhor de fazer isso do que preencher o xaml com crud?

Editar

Usar valores de fallback parece não ser uma solução, porque também não está conseguindo encontrar recursos:

System.Windows.ResourceDictionary Warning: 9 : Resource not found; ResourceKey='Img_Folder_Closed_Ex'

É como se estivesse esquecendo tudo no dicionário de recursos, gerando todos esses erros espúrios e, em seguida, lembrando tudo de novo e exibindo ok.

Editar

Ok, eu reduzi isso um pouco mais, comentando todas as ligações e colocando-as de volta uma a uma e resolvendo os problemas ao longo do caminho, agora ela carrega e eu posso clicar nos itens e nenhum diagnóstico é produzido até que .. Quando clico no botão que muda os itens da árvore, ele enlouquece e expele centenas de erros. Aqui está um pequeno subconjunto dos erros:

System.Windows.Data Information: 21 : BindingExpression cannot retrieve value from null data item. This could happen when binding is detached or when binding to a Nullable type that has no value. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 41 : BindingExpression path error: 'IsFolder' property not found for 'object' because data item is null.  This could happen because the data provider has not produced any data yet. BindingExpression:Path=IsFolder; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 20 :System.Windows.Data Information: 21 : BindingExpression cannot retrieve value from null data item. This could happen when binding is detached or when binding to a Nullable type that has no value. BindingExpression:Path=IsFolder; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=IsFolder; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.ResourceDictionary Warning: 9 : Resource not found; ResourceKey='Img_QA'
System.Windows.Data Information: 41 : BindingExpression path error: 'IsIncluded' property not found for 'object' because data item is null.  This could happen because the data provider has not produced any data yet. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
 BindingExpression cannot retrieve value due to missing information. BindingExpression:Path=IsFolder; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 21 : BindingExpression cannot retrieve value from null data item. This could happen when binding is detached or when binding to a Nullable type that has no value. BindingExpression:Path=IsFolder; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=IsFolder; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 41 : BindingExpression path error: 'IsIncluded' property not found for 'object' because data item is null.  This could happen because the data provider has noSystem.Windows.Data Information: 20 : BindingExpression cannot retrieve value due to missing information. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 21 : BindingExpression cannot retrieve value from null data item. This could happen when binding is detached or when binding to a Nullable type that has no value. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
t produced any data yet. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 20 : BindingExpression cannot retrieve value due to missing information. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 21 : BindingExpression cannot retrieve value from null data item. This could happen when binding is detached or when binding to a Nullable type that has no value. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=IsIncluded; DataItem=null; target element is 'TreeViewItemIcon' (Name=''); target property is 'NoTarSystem.Windows.ResourceDictionary Warning: 9 : Resource not found; ResourceKey='Img_QA'
System.Windows.Data Information: 41 : BindingExpression path error: 'Name' property not found for 'object' because data item is null.  This could happen because the data provider has not produced any data yet. BindingExpression:Path=Name; DataItem=null; target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')
System.Windows.Data Information: 20 : BindingExpression cannot retrieve value due to missing information. BindingExpression:Path=Name; DataItem=null; target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')
System.Windows.Data Information: 21 : BindingExpression cannot retrieve value from null data item. This could happen when binding is detached or when binding to a Nullable type that has no value. BindingExpression:Path=Name; DataItem=null; target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')
System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=Name; DataItem=null; target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')
get' (type 'Object')

Se eu alterar o manipulador de botão para apenas definir ItemsSource para uma lista vazia, ele gerará o mesmo conjunto enorme de erros. Parece que quando a fonte é desconectada, o WPF reavalia todas as ligações e como seria de esperar, todas falhariam.

Editar

Para simplificar ...

ItemsSource está vinculado a um ObservableCollection.Eu chamo Clear () no ObservableCollection.Todas as ligações são reavaliadas e não podem mais encontrar seus dados (porque foram removidas)Em última análise, todos os itens são removidos

Por que essas ligações estão sendo reavaliadas? Existe uma maneira de obtê-lo para remover os itens sem todo esse trabalho extra?

Editar

Eu criei um projeto que exibe parte do problema. Ele gera erros reclamando que recursos não podem ser encontrados ao chamar Clear (), mas não produz as mensagens dataItem = null. Vou continuar tentando reproduzir aqueles com o exemplo simples. Infelizmente eu estou bloqueado de pastebin e afins pelo firewall, então aqui está o código que é alterado a partir do aplicativo WPF padrão ...

App.xaml:

<Application x:Class="ObservableCollectionTest.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <Style x:Key="{x:Type TreeViewItem}" TargetType="{x:Type TreeViewItem}">
            <Setter Property="HorizontalContentAlignment" Value="Left" />
            <Setter Property="VerticalContentAlignment" Value="Center" />
        </Style>
    </Application.Resources>
</Application>

MainWindow.xaml:

<Window x:Class="ObservableCollectionTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:l="clr-namespace:ObservableCollectionTest"
        Title="MainWindow" Height="350" Width="525">

    <Window.Resources>

        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="/ObservableCollectionTest;component/Theme.xaml" />
            </ResourceDictionary.MergedDictionaries>

            <l:Model x:Key="TheModel" />

        </ResourceDictionary>

    </Window.Resources>

    <Grid>
        <Grid.Resources>
            <ObjectDataProvider x:Key="TheModelProvider" ObjectInstance="{StaticResource TheModel}" />

            <HierarchicalDataTemplate
                x:Key="TheModelTemplate"
                DataType="{x:Type l:TestItem}"
                ItemsSource="{Binding Items}">
                <StackPanel Orientation="Horizontal">
                    <Image Style="{DynamicResource ImageStyle}" />
                    <Label>
                        <TextBlock Style="{DynamicResource TextBlockStyle}" Text="{Binding Name}" />
                    </Label>
                </StackPanel>
            </HierarchicalDataTemplate>
        </Grid.Resources>
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <TreeView
            ItemsSource="{Binding Source={StaticResource TheModelProvider}, Path=Items}"
            ItemTemplate="{StaticResource TheModelTemplate}"/>

        <Button
            Grid.Row="1"
            Height="30"
            Content="Empty the list"
            Click="EmptyTheList_Click" />
    </Grid>
</Window>

MainWindow.cs:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace ObservableCollectionTest
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            PresentationTraceSources.DataBindingSource.Listeners.Add(
                    new ConsoleTraceListener());

            PresentationTraceSources.DataBindingSource.Switch.Level = SourceLevels.All;

            InitializeComponent();
        }

        private void EmptyTheList_Click(object sender, RoutedEventArgs e)
        {
            (Resources["TheModel"] as Model).Items.Clear();
        }
    }
}

Model.cs:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;

namespace ObservableCollectionTest
{
    class Model
    {
        public ObservableCollection<TestItem> Items { get; set; }

        public Model()
        {
            Items = new ObservableCollection<TestItem>()
            {
                new TestItem()
                {
                    Name = "TopLevel",
                    Items = new List<TestItem>()
                    {
                        new TestItem() { Name = "Item1", Items = new List<TestItem>() },
                        new TestItem()
                        {
                            Name = "Item2",
                            Items = new List<TestItem>()
                            {
                                new TestItem() { Name = "SubItem1", Items = new List<TestItem>() },
                                new TestItem() { Name = "SubItem2", Items = new List<TestItem>() },
                                new TestItem() { Name = "SubItem3", Items = new List<TestItem>() }
                            }
                        },
                        new TestItem() { Name = "Item3", Items = new List<TestItem>() },
                        new TestItem() { Name = "Item4", Items = new List<TestItem>() }
                    }
                }
            };
        }
    }

    class TestItem
    {
        public string Name { get; set; }

        public bool IsRoot { get { return Name == "TopLevel"; } }

        public List<TestItem> Items { get; set; }
    }
}

Theme.xaml:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="/ObservableCollectionTest;component/Common.xaml" />
    </ResourceDictionary.MergedDictionaries>

    <BitmapImage x:Key="Img_Folder_Open_In" UriSource="/ObservableCollectionTest;component/VS11_Light_Folder_Open_In.png" />
    <BitmapImage x:Key="Img_Folder_Closed_In" UriSource="/ObservableCollectionTest;component/VS11_Light_Folder_Closed_In.png" />

</ResourceDictionary>

Common.xaml:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <Style x:Key="TextBlockStyle" TargetType="TextBlock">
        <Setter Property="Foreground" Value="Blue" />
        <Setter Property="Background" Value="Yellow" />

        <Style.Triggers>
            <MultiDataTrigger>
                <MultiDataTrigger.Conditions>
                    <Condition Binding="{Binding Name}" Value="TopLevel" />
                    <Condition Binding="{Binding IsExpanded, RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type TreeViewItem}}, FallbackValue=False}" Value="True" />
                </MultiDataTrigger.Conditions>
                <Setter Property="Background" Value="Red" />
            </MultiDataTrigger>
        </Style.Triggers>
    </Style>

    <Style x:Key="ImageStyle" TargetType="{x:Type Image}">
        <Style.Triggers>
            <MultiDataTrigger>
                <MultiDataTrigger.Conditions>
                    <Condition Binding="{Binding IsRoot}" Value="False" />
                    <Condition Binding="{Binding IsExpanded, RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type TreeViewItem}}, FallbackValue=False}" Value="True" />
                </MultiDataTrigger.Conditions>
                <Setter Property="Source" Value="{DynamicResource Img_Folder_Open_In}" />
            </MultiDataTrigger>

            <MultiDataTrigger>
                <MultiDataTrigger.Conditions>
                    <Condition Binding="{Binding IsRoot}" Value="False" />
                    <Condition Binding="{Binding IsExpanded, RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type TreeViewItem}}, FallbackValue=False}" Value="False" />
                </MultiDataTrigger.Conditions>
                <Setter Property="Source" Value="{DynamicResource Img_Folder_Closed_In}" />
            </MultiDataTrigger>
        </Style.Triggers>
    </Style>

</ResourceDictionary>

FWIW, eu também estou usando o .NET 3.5 (infelizmente tenho) mas esse problema apareceu com o .NET 4.0 também.

Eu também tenho duas imagens no projeto:

 (VS11_Light_Folder_Closed_In.png) (VS11_Light_Folder_Open_In.png)

Editar

Tentei mudar oObjectDataProvider para usar DynamicResource:

<ObjectDataProvider x:Key="TheModelProvider" ObjectInstance="{DynamicResource TheModel}" />

Mas isso gerou essa exceção: