How to Perform an Asynchronous Query by Using System.Management

Artigo
05/03/2011

Applies To: System Center Configuration Manager 2007, System Center Configuration Manager 2007 R2, System Center Configuration Manager 2007 R3, System Center Configuration Manager 2007 SP1, System Center Configuration Manager 2007 SP2

To perform an asynchronous query on a Microsoft System Center Configuration Manager 2007 client Windows Instrumentation (WMI) namespace, create a ManagementObjectSearcher object that specifies a WQL query. You then create a ManagementOperationObserver that specifies an event handler for each query result and also for the end of the query.

The asynchronous query is run when the ManagementObjectSearcher object Get method is called with the ManagementOperationObserver object.

To perform an asynchronous query

Set up a connection to the Configuration Manager 2007 client WMI namespace. For more information, see How to Connect to the Configuration Manager Client WMI Namespace by Using System.Management.
Create a ManagementObjectSearcher object.
Create a ManagementOperationObserver object.
Add an ObjectReadyEventHandler method the ManagementOperationObserver object.
Add a CompletedEventHandler method to the ManagementOperationObserver.
Call the ManagementObjectSearcher object Get method and supply the ManagmentOperationObserver object as a parameter.
Ensure you application still runs while the query is run.

Example

The following C# code example asynchronously queries for components that are installed on a client.

For information about calling the sample code, see How to Call a WMI Class Method by Using System.Management.

public void EnumerateInstancesAsync(ManagementScope scope)
{
    try
    {
        // Instantiate an object searcher with the query.
        ManagementObjectSearcher searcher =
            new ManagementObjectSearcher(scope, new
            SelectQuery("CCM_InstalledComponent"));

        // Create a results watcher object
        // and handler for results and completion.
        ManagementOperationObserver results = new
            ManagementOperationObserver();

        // Attach handler to events for results and completion.
        results.ObjectReady += new
            ObjectReadyEventHandler(this.NewObject);
        results.Completed += new
            CompletedEventHandler(this.Done);

        Console.WriteLine("Installed Components");
        Console.WriteLine("--------------------");
        Console.WriteLine();

        // Call the asynchronous overload of Get()
        // to start the enumeration.
        searcher.Get(results);

        // Do something else while results
        // arrive asynchronously.
        while (!this.Completed)
        {
            System.Threading.Thread.Sleep(1000);
        }

        this.Reset();
    }
    catch (ManagementException e)
    {
        Console.WriteLine("Failed to run query: " + e.Message);
        throw;
    }

}

private bool isCompleted = false;

private void NewObject(object sender,
    ObjectReadyEventArgs obj)
{
    try
    {
        Console.WriteLine("Name: {0}, Version = {1}",
            obj.NewObject["DisplayName"],
            obj.NewObject["Version"]);
    }
    catch (ManagementException e)
    {
        Console.WriteLine("Error: " + e.Message);
    }

}

private bool Completed
{
    get
    {
        return isCompleted;
    }
}

private void Reset()
{
    isCompleted = false;
}

private void Done(object sender,
         CompletedEventArgs obj)
{
    isCompleted = true;
}

This example method has the following parameters:

Parameter	Type	Description
Scope	ManagementScope	A valid ManagementScope. The path should be root\ccm.

Compiling the Code

Namespaces

System.

System.Management.

Assembly

System.Management.

Robust Programming

The exception that can be raised is System.Management.ManagementException.

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