ArcGIS图层和要素的过滤显示

ArcGIS可以设置动态地图服务（ArcGISDynamicMapServiceLayer）显示哪些图层，也可以设置每个图层根据某个属性字段的某些条件来进行过滤显示。

1、设置显示的图层

主要是通过ArcGISDynamicMapServiceLayer的VisibleLayers属性来设置或得到当前显示的图层，C#代码如下：

代码中Map1和TextBlock_VisibleLayers是已经定义好的地图和TextBlock控件。

//ArcGISDynamicMapServiceLayer初始化函数
private void ArcGISDynamicMapServiceLayer_Initialized(object sender, System.EventArgs e)
{
    //得到ArcGISDynamicMapServiceLayer，这里是第一个图层，根据实际情况，可以通过Map.Layers["图层的ID"]来得到
    ArcGISDynamicMapServiceLayer myArcGISDynamicMapServiceLayer = (ArcGISDynamicMapServiceLayer)Map1.Layers[];

    //VisibleLayers的读写

    //下面注释的代码：设置myArcGISDynamicMapServiceLayer第二和第三个图层显示
    //int[] myVisibleLayers2 = { 1, 2 };
    //myArcGISDynamicMapServiceLayer.VisibleLayers = myVisibleLayers2;

    //得到显示的图层ID
    int[] myVisibleLayers = myArcGISDynamicMapServiceLayer.VisibleLayers;
    if (myVisibleLayers != null)
    {
        string myVisibleLayersText = "Number VisibleLayers: " + myVisibleLayers.Length.ToString();
        string myVisibleLayersText2 = "";
        int i = ;
        for (i = ; i < myVisibleLayers.Length; ++i)
        {
            myVisibleLayersText2 = myVisibleLayersText2 + " " + myVisibleLayers[i].ToString();
        }
        TextBlock_VisibleLayers.Text = myVisibleLayersText + ". VisibleLayers ID's: " + myVisibleLayersText2;
    }
    else
    {
        TextBlock_VisibleLayers.Text = "[VisibleLayers not set - Meaning all layers are visible.]";
    }
}

2、设置图层根据字段条件过滤显示

如果不全部显示一个图层的所有要素，而是根据某些条件来“过滤显示”，则可以通过设置LayerDefinition来实现。

LayerDefinition的设置可以通过XAML代码实现：

<StackPanel Name="StackPanel1" Height="400" Width="400" Margin="0,0,0,0" HorizontalAlignment="Left" VerticalAlignment="Top" >
    <esri:Map Background="White" Name="Map1" Height="200" Width="400">

         <!-- Set the LayerDefinition for the ArcGISDynamicMapServiceLayer. -->
         <!-- By default no LayerDefinition is set unless explicitly set on the server. -->
         <esri:ArcGISDynamicMapServiceLayer
              Url="http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Earthquakes/Since_1970/MapServer" />
              <esri:ArcGISDynamicMapServiceLayer.LayerDefinitions>

                  <!-- LayerID="0" is the Earthquakes1970 layer. The Definition only displays earth quakes that have a
                          Magnitude greater than 6. The field Magnitude is of type esriFieldTypeDouble. -->
                  <esri:LayerDefinition LayerID="0" Definition="Magnitude > 6" />

                  <!-- LayerID="0" is the Earthquakes1970 layer. The Definition only displays earth quakes that have a
                          Magnitude greater than 3 and less than 6. The field Magnitude is of type esriFieldTypeDouble. -->
                  <!-- <esri:LayerDefinition LayerID="0" Definition="Magnitude > 3 AND Magnitude &lt; 6" /> -->

                  <!-- Another example where the Name of the earth quake event is to contains the letters 'CHINA'.
                          Note: the Definition is case sensitive. The field Name is of type esriFieldTypeString. -->
                  <!-- <esri:LayerDefinition LayerID="0" Definition="Name LIKE 'CHINA'" /> -->

                  <!-- Another example where the Name of the earth quake event is exactly matches the letters 'VENEZUELA'.
                          Note: the Definition is case sensitive. The field Name is of type esriFieldTypeString. -->
                  <!-- <esri:LayerDefinition LayerID="0" Definition="Name = 'VENEZUELA'" /> -->

                  <!-- Another example where the earth quake events are displayed if they occured after January 15, 2000.
                          The field Date_ is of type esriFieldTypeDate. -->
                  <!-- <esri:LayerDefinition LayerID="0" Definition="Date_ > DATE '1/15/2000'" />-->

              </esri:ArcGISDynamicMapServiceLayer.LayerDefinitions>
         </esri:ArcGISDynamicMapServiceLayer>
    </esri:Map>

    <!-- LayerDefinitions Property (Read) -->
    <TextBlock Height="23" Name="TextBlock_LayerDefinitions"
        Text="{Binding ElementName=Map1, Path=Layers[0].LayerDefinitions[0].Definition}" />
</StackPanel>

也可以通过代码来实现，C#代码如下：

//ArcGISDynamicMapServiceLayer初始化函数
private void ArcGISDynamicMapServiceLayer_Initialized(object sender, System.EventArgs e)
{
    //得到ArcGISDynamicMapServiceLayer，这里是第一个图层，根据实际情况，可以通过Map.Layers["图层的ID"]来得到
    ArcGISDynamicMapServiceLayer myArcGISDynamicMapServiceLayer = (ArcGISDynamicMapServiceLayer)Map1.Layers[];

    //LayerDefinition的读写

    //设置图层的LayerDefinition，默认情况下LayerDefinition是没有设置的
    //得到图层的LayerDefinition
    ESRI.ArcGIS.Client.LayerDefinition myDefinition = new ESRI.ArcGIS.Client.LayerDefinition();
    myDefinition.LayerID = ;

    //设置LayerDefinition，属性字段“Magnitude”属于ID为0的图层
    //LayerDefinition的设置语句和Query中的Where语句一样
    //字段Magnitude的类型是esriFieldTypeDouble.
    myDefinition.Definition = "Magnitude > 6";

    // The Definition only displays earth quakes that have a Magnitude greater than 3 and less that 6.
    // The field Magnitude is of type esriFieldTypeDouble.
    // myDefinition.Definition = "Magnitude > 3 AND Magnitude < 6";

    // Another example where the Name of the earth quake event is to contains the letters 'CHINA'.
    // Note: the Definition is case sensitive. The field Name is of type esriFieldTypeString.
    //myDefinition.Definition = "Name LIKE 'CHINA'";

    // Another example where the Name of the earth quake event is exactly matches the letters 'VENEZUELA'.
    // Note: the Definition is case sensitive. The field Name is of type esriFieldTypeString.
    //myDefinition.Definition = "Name = 'VENEZUELA'";

    // Another example where the earth quake events are displayed if they occured after January 15, 2000.
    // The field Date_ is of type esriFieldTypeDate.
    //myDefinition.Definition = "Date_ > DATE '1/15/2000'";

    //创建一个ObservableCollection，add设置的LayerDefinition
    System.Collections.ObjectModel.ObservableCollection<LayerDefinition> myObservableCollection2 =
       new System.Collections.ObjectModel.ObservableCollection<LayerDefinition>();
    myObservableCollection2.Add(myDefinition);

    //启动设置的LayerDefinition
    myArcGISDynamicMapServiceLayer.LayerDefinitions = myObservableCollection2;

    //得到已经存在的LayerDefinitions collection.
    System.Collections.ObjectModel.ObservableCollection<LayerDefinition> myObservableCollection =
        myArcGISDynamicMapServiceLayer.LayerDefinitions;

    if (myObservableCollection.Count > )
    {
        //得到第一个LayerDefinition
        ESRI.ArcGIS.Client.LayerDefinition myLayerDefinition = myObservableCollection[];

        //得到LayerDefinition的信息
        TextBlock_LayerDefinitions.Text = "For Layer: " + myLayerDefinition.LayerID.ToString() +
            ". The Defintion is: " + myLayerDefinition.Definition;
    }
    else
    {
        TextBlock_LayerDefinitions.Text = "[NO LayerDefinitions SET]";
    }
}

上面ArcGISDynamicMapServiceLayer_Initialized(object sender, System.EventArgs e)函数是订阅到ArcGISDynamicMapServiceLayer.Initialized的，也就是在图层加载的时候就设置了“过滤”条件，如果要在后期在某个响应事件中动态的刷新地图，需要在设置LayerDefinition后，调用ArcGISDynamicMapServiceLayer.Refresh()函数来刷新地图才能看到效果。

参考：

http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.ArcGISDynamicMapServiceLayer~VisibleLayers.html

http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.ArcGISDynamicMapServiceLayer~LayerDefinitions.html