Callback meethod not being executed for a service call in silverlight

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Silverlight

Hi All,

I am working on a silverlight project using MVVM pattern. Here I have some validations that are being performed by SP's. I just have to call the SP to perform these validations and based on the data returned by the service call I have to continue executing save method. Please see the below sample code.

public void Save()
{
    preSaveValidations();
    if(continueSave==false) //This value will be set in call back method validation service call
          return;

    //Here goes actual service call to save the modifications
}

public void preSaveValidations()
{
    _dataContext.CallValidate(callVaildate_CallBack, null);
}

public void callValidate_CallBack(InvokeOperation<\IEnumerable<\CallValidate_Result>> e)
{
  if(e.HasError==false)
   {
     if(e.Value!=null)
      {
         continueSave=true; // This is the parameter used to continue save method
      }
   }
}

Now the problem is when i run this code, callValidate_CallBack is not being executed, instead code present after preSaveValidations() is being exected, which is resulting in wrong functionality.

Simply, I just want to stop the execution of other code, until results from call back method are generated.

Suggestions please. . .