Restrict maximum zoom level till 45 meter

[JulieBiju]

How to set map maximum zoom level till 45 meter and 100ft ....If user will zoom more then I am getting "No data available" message on Bing map.So how to restrict that?
I am using the code below for zooming map.But dont know how to restrict it till 45 meter..

Dim expandPercentage As Double = 400
                Dim selectedFeatureExtent As ESRI.ArcGIS.Client.Geometry.Envelope = graphicsLayer.FullExtent
                 expandPercentage = 100
                 Dim widthExpand As Double = selectedFeatureExtent.Width * (expandPercentage / 100)
                Dim heightExpand As Double = selectedFeatureExtent.Height * (expandPercentage / 100)
                Dim displayExtent As New ESRI.ArcGIS.Client.Geometry.Envelope(selectedFeatureExtent.XMin - (widthExpand / 2), selectedFeatureExtent.YMin - (heightExpand / 2), selectedFeatureExtent.XMax + (widthExpand / 2), selectedFeatureExtent.YMax + (heightExpand / 2))
                MyMap.ZoomTo(displayExtent)

Map is like below

  <esri:Map Extent="-120, 20, -100, 40"  Grid.Row="1" Grid.Column="1"  Name="MyMap"  Visibility="Visible" Background="Transparent" ....................

[AhmedEl-Sisi]

You can set Map Minimum Resolution in your XAML or by code.

[DominiqueBroux]

Additionally to cc4ever solution, the issue may also be coming when you select a point feature only. Such a feature has no extent, so you might have to use a minimum extent size.

Something like:

Dim minExtentSize As Double = 45
Dim widthExpand As Double = Math.Min(selectedFeatureExtent.Width * (expandPercentage / 100), minExtentSize)
Dim heightExpand As Double = Math.Min(selectedFeatureExtent.Height * (expandPercentage / 100), minExtentSize)