La propriété de dépendance ne sera pas définie

Question

J'ai configuré une propriété de dépendance sur mon contrôle GISPointSelecter de la manière habituelle.

public static readonly DependencyProperty GISMapProperty = DependencyProperty.Register(nameof(GISMap), typeof(GISControl), typeof(GISPointSelecter), new PropertyMetadata(null)); 

public GISControl GISMap 
{ 
    get 
    { 
     return (GISControl)GetValue(GISMapProperty); 
    } 
    set 
    { 
     SetValue(GISMapProperty, value); 
    } 
} 

Mais quand je vais charger cette XAML ...

<Grid xmlns="http://schemas.microsoft.com/client/2007" xmlns:dataInput="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data.Input" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk" xmlns:datavis="clr-namespace:System.Windows.Controls.DataVisualization;assembly=System.Windows.Controls.DataVisualization.Toolkit" xmlns:charting="clr-namespace:System.Windows.Controls.DataVisualization.Charting;assembly=System.Windows.Controls.DataVisualization.Toolkit" xmlns:xivic="clr-namespace:Adapt.Presentation.Xivic;assembly=Adapt.Presentation.Xivic" xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls" xmlns:xiviccontrols="clr-namespace:Adapt.Presentation.XivicControls;assembly=Adapt.Presentation.XivicControls" xmlns:fw="clr-namespace:System.Windows.Controls;assembly=FloatableWindow" xmlns:adaptcontrols="clr-namespace:Adapt.Presentation.Controls;assembly=Adapt.Presentation.Controls" xmlns:PivotSDK="clr-namespace:System.Windows.Controls.Pivot;assembly=System.Windows.Controls.Pivot" xmlns:query="clr-namespace:Adapt.Model.Data;assembly=Adapt.Model.Common.Silverlight" xmlns:data="clr-namespace:Adapt.Presentation.Data;assembly=Adapt.Presentation.XivicControls" xmlns:adaptdata="clr-namespace:Adapt.Model.Data;assembly=Adapt.Model.Common.Silverlight" xmlns:sys="clr-namespace:System;assembly=mscorlib"> 
<xiviccontrols:GISPointSelecter Name="GISMapControl" MiniMenuTrackButtons="Visible"> 
    <xiviccontrols:GISPointSelecter.GISMap> 
     <xiviccontrols:GISControl x:Name="GISMap1" AutoMarkingEnabled="True" EsriOfflineZoomOutDisplay="300" DontRenderFullExtent="False" > 

      <xiviccontrols:GISControl.LocationTypes> 
       <sys:String>ShapeKey</sys:String> 
      </xiviccontrols:GISControl.LocationTypes> 

      <xiviccontrols:GISControl.LocationReferences> 
       <sys:String>Asset.GISKey</sys:String> 
      </xiviccontrols:GISControl.LocationReferences> 

      <xiviccontrols:GISControl.OverlayReferences> 
       <sys:String>, TaskDetail_, , Open Task, New Task</sys:String> 
      </xiviccontrols:GISControl.OverlayReferences> 

      <xiviccontrols:GISControl.MarkerConditionEquations> 
       <sys:String>OverallResultTag = Red</sys:String> 
       <sys:String>OverallResultTag = Yellow</sys:String> 
       <sys:String>OverallResultTag = Orange</sys:String> 
       <sys:String>OverallResultTag = Blue</sys:String> 
       <sys:String>OverallResultTag = No</sys:String> 
       <sys:String>OverallResultTag = </sys:String> 
      </xiviccontrols:GISControl.MarkerConditionEquations> 

      <xiviccontrols:GISControl.MarkerConditionColours> 
       <sys:String>Red</sys:String> 
       <sys:String>Yellow</sys:String> 
       <sys:String>Orange</sys:String> 
       <sys:String>Blue</sys:String> 
       <sys:String>Green</sys:String> 
       <sys:String>White</sys:String> 
      </xiviccontrols:GISControl.MarkerConditionColours> 

      <xiviccontrols:GISControl.AutoMarkLayers> 
       <xiviccontrols:AutoMarkLayer AssetForeignKey="Asset" LayerKey="f38d3a14-9fec-495c-b524-c96bec5443f7" MinExtentLongitude="4000" MarkerDataType="Adapt.Model.TaskManagement.TaskInfo"> 
        <xiviccontrols:AutoMarkLayer.MarkerDataQuery> 

         <adaptdata:DataQuery FromTableAlias="Tasks"> 
          <adaptdata:DataQuery.WhereClauses> 
           <adaptdata:WhereClauseJoiner>OpenBracket</adaptdata:WhereClauseJoiner> 
           <adaptdata:WhereClause LeftExpression="Tasks.Activity" WhereClauseType="Equals" RightExpression="1" /> 
           <adaptdata:WhereClauseJoiner>Or</adaptdata:WhereClauseJoiner> 
           <adaptdata:WhereClause LeftExpression="Tasks.Activity" WhereClauseType="Equals" RightExpression="5" /> 
           <adaptdata:WhereClauseJoiner>Or</adaptdata:WhereClauseJoiner> 
           <adaptdata:WhereClause LeftExpression="Tasks.Activity" WhereClauseType="Equals" RightExpression="6" /> 
           <adaptdata:WhereClauseJoiner>Or</adaptdata:WhereClauseJoiner> 
           <adaptdata:WhereClause LeftExpression="Tasks.Activity" WhereClauseType="Equals" RightExpression="7" /> 
           <adaptdata:WhereClauseJoiner>CloseBracket</adaptdata:WhereClauseJoiner> 
           <adaptdata:WhereClauseJoiner>And</adaptdata:WhereClauseJoiner> 
           <adaptdata:WhereClause LeftExpression="Tasks.StatusKey" WhereClauseType="Equals" RightExpression="2" /> 
          </adaptdata:DataQuery.WhereClauses> 
         </adaptdata:DataQuery> 

        </xiviccontrols:AutoMarkLayer.MarkerDataQuery> 
       </xiviccontrols:AutoMarkLayer> 
      </xiviccontrols:GISControl.AutoMarkLayers> 

     </xiviccontrols:GISControl> 
    </xiviccontrols:GISPointSelecter.GISMap> 
</xiviccontrols:GISPointSelecter> 

... La propriété est pas définie, par défaut à null, puis-je obtenir un NullReferenceException dans la GISPointSelecter constructeur.

public GISPointSelecter() 
{ 
    InitializeComponent(); 

    GISMap.LeftIndent = 145; 
    LayoutRoot.Children.Insert(0, GISMap); 
    GISMap.Click += new GISControl.GISControlClickedDelegate(Map_Click); 
    GISMap.GISRequestedCloseSplash += new EventHandler<EventArgs>(GISMap_GISRequestedCloseSplash); 

    ViewAssetsMiniMenu.XamlProviderLoaded += new EventHandler<EventArgs>(ViewAssetsMiniMenu_XamlProviderLoaded); 
} 

Qu'est-ce que je fais mal?

Answer 1

Vous référencez la propriété GISMap dans le constructeur. La propriété GISMap sera toujours nulle dans le constructeur car elle n'aura pas eu la chance d'être définie à ce point, ce qui explique pourquoi vous obtenez une exception NullReferenceException.

Vous devriez plutôt enregistrer un PropertyChangedCallback pour être averti des changements de valeur de la propriété:

public static readonly DependencyProperty GISMapProperty = DependencyProperty.Register(
    nameof(GISMap), typeof(GISControl), typeof(GISPointSelecter), 
    new PropertyMetadata(GISMapPropertyChanged)); 

private static void GISMapPropertyChanged(
    DependencyObject o, DependencyPropertyChangedEventArgs e) 
{ 
    ((GISPointSelecter)o).GISMapPropertyChanged(
     (GISControl)e.OldValue, (GISControl)e.NewValue); 
} 

private void GISMapPropertyChanged(GISControl oldGisMap, GISControl newGisMap) 
{ 
    if (oldGisMap != null) 
    { 
     LayoutRoot.Children.Remove(oldGisMap); 
     oldGisMap.Click -= Map_Click; 
     oldGisMap.GISRequestedCloseSplash -= GISMap_GISRequestedCloseSplash; 
    } 

    if (newGisMap != null) 
    { 
     LayoutRoot.Children.Insert(0, newGisMap); 
     newGisMap.Click += Map_Click; 
     newGisMap.GISRequestedCloseSplash += GISMap_GISRequestedCloseSplash; 
    } 
}