Thursday, 24 October 2013

Using Snoop and PowerShell to interrogate View Models in WPF applications

It is possible to use Snoop to interrogate View Models in WPF applications. If you first install Snoop, check that you run Snoop as an administrator, if you cannot attach to the process which is your WPF application. Start snooping the application, then move to the tab Powershell. Use Ctrl+Shift and click on the visual or ui element you want to inspect in the GUI. You will see a pink border around the ui element or visual and this will then be possible to inspect further. Go to the PowerShell tab and start interrogating the object. In the MVVM WPF application at my work, we can see the view model in the property DataContext.ViewModel. It is possible to further drill down to properties in the ViewModel quite easily. Example follows, I have selected a RadGridView in my application and select the Visual property, then look at the DataContext of the Visual, drill down further to the ModelCollection property, which in this particular example is a property of the data context object of which the selected visual is data bound to. This object contains a property of type ObservableCollection which has got some custom object inside. The collection object is then piped to the Select operator in Powershell and this Select operator projects the properties of each object in the ModelCollection, in this particular case I select OperationId, OperatingDate and OperationStatus. This is then further piped to Format-Table which is used with the argument -autoresize. The resulting selector is then:

$selected.Visual.DataContext.ModelCollection | Select OperationId, OperatingDate, OperationStatus | Format-Table -autosize

OperationId OperatingDate       OperationStatus
----------- -------------       ---------------
       2076                              Urgent
         70                              Urgent
       2162 23.10.2013 00:00:00       Operation
       2165 23.10.2013 00:00:00       Operation
       2196 23.10.2013 00:00:00       Operation
       2197 23.10.2013 00:00:00       Operation
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
          0 23.10.2013 00:00:00            None
       1913                              Urgent
       2192 23.10.2013 00:00:00       Operation
       2193 23.10.2013 00:00:00       Operation
       2194 23.10.2013 00:00:00       Operation
       2013 23.10.2013 00:00:00       Operation
       2195 23.10.2013 00:00:00       Operation
       2161 23.10.2013 00:00:00       Operation


It could be possible to pipe this further to the Export-Csv Powershell cmdlet and you can have Excel launch the resulting .csv file. This shows how SnoopWpf can be used to do powerful runtime analysis and inspection of WPF applications and also support Powershell operators. Both technical testers and WPF developers will find this useful. To get started, install Snoop Wpf created by the brilliant developer Cory Plotts and can be downloaded from here: Snoop WPF

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