Suppress New Processes Initiated by .NET Controls

• Nov 26, 2020
• 3 minutes to read

DevExpress controls can start new processes in response to user actions. For example, the RichEdit or HyperlinkEdit controls can open the system’s default browser when a user clicks a hyperlink. If you use v19.1 or later, you can use the DevExpress.Data.Utils.ProcessStartPolicy class to apply a policy that manages processes.

Process Start Policies

To apply a policy, call one of the following methods of the DevExpress.Data.Utils.ProcessStartPolicy class at application startup:

• SuppressAll() - Applies a policy that suppresses all new processes.
• ThrowAlways() - Applies a policy that throws an exception when a process is about to start.
• RequireConfirmation() - Applies a policy that shows a confirmation dialog that prompts a user to confirm or cancel a process.

If none of these methods is called, DevExpress controls allow all processes to start. All exceptions that indicate failed processes are suppressed.

The following code suppresses all user-invoked processes:

C#

static void Main() {  
    DevExpress.Data.Utils.ProcessStartPolicy.SuppressAll();  
    //...  
}  

VB.NET

Shared Sub Main()  
    DevExpress.Data.Utils.ProcessStartPolicy.SuppressAll()  
    Application.EnableVisualStyles()  
    Application.SetCompatibleTextRenderingDefault(False)  
    Application.Run(New Form1)  
End Sub

Trusted Resources

The ThrowAlways and RequireConfirmation policies allow you to setup trusted documents, commands, or URLs. Processes for trusted resources bypass exceptions or confirmation dialogs.

To register a trusted resource, use the static RegisterTrustedProcess method:

C#

DevExpress.Data.Utils.ProcessStartPolicy.RegisterTrustedProcess("https://www.devexpress.com");

VB.NET

DevExpress.Data.Utils.ProcessStartPolicy.RegisterTrustedProcess("https://www.devexpress.com") 

Process Start Events

To perform custom actions when a DevExpress control starts a process, use the following two events of the ProcessStartPolicy class:

• Starting - Fires before a process starts and allows you to cancel the process.

  C#

  static void Main() {
    ProcessStartPolicy.Starting += ProcessStartPolicy_Starting;
    // ...
  }
  private static void ProcessStartPolicy_Starting(object sender, System.ComponentModel.CancelEventArgs e) {
    ProcessStartInfo psi = sender as ProcessStartInfo;
    e.Cancel = !psi.FileName.Contains("www.devexpress.com");
  }
  

  VB.NET

  Shared Sub Main()
    AddHandler ProcessStartPolicy.Starting, AddressOf ProcessStartPolicy_Starting
    ' ...
  End Sub
  Private Shared Sub ProcessStartPolicy_Starting(sender As Object, e As CancelEventArgs)
    Dim psi As ProcessStartInfo = CType(sender, ProcessStartInfo)
    e.Cancel = Not psi.FileName.Contains("www.devexpress.com")
  End Sub
  

• Started - Fires after a process is started. This is a notification event.
  C#

  static void Main() {
    ProcessStartPolicy.Started += ProcessStartPolicy_Started;
    // ...
  }
  private static void ProcessStartPolicy_Started(object sender, EventArgs e) {
    Process process = sender as Process;
    // ...
    // Log.WriteMessage("process started");
  }
  

  VB.NET

  Shared Sub Main()
    AddHandler ProcessStartPolicy.Started, AddressOf ProcessStartPolicy_Started
    ' ...
  End Sub
  Private Shared Sub ProcessStartPolicy_Started(sender As Object, e As EventArgs)
    Dim process As Process = CType(sender, Process)
    ' ...
    ' Log.WriteMessage("process started")
  End Sub
  

Process Start Failures

Exceptions are not raised if a process fails to start. To throw exceptions in this case, call the static ThrowOnErrors method at application startup. You can also handle the Failed event to respond to these failures. The following code handles the Failed event to suppress an internal exception and display a message box.

C#

static void Main() {  
    DevExpress.Data.Utils.ProcessStartPolicy.Failed += ProcessStartPolicy_Failed;  
    //...  
}  

private static void ProcessStartPolicy_Failed(object sender, DevExpress.Data.Utils.ProcessStartPolicy.ProcessStartFailedExceptionEventArgs e) {  
    if(e.Exception is Win32Exception) {  
        System.Diagnostics.ProcessStartInfo si = sender as System.Diagnostics.ProcessStartInfo;  
        e.Throw = false;  
        MessageBox.Show("File not found: " + si.FileName);  
    }  
}  

VB.NET

Public Class Form1  
    Shared Sub Main()  
        AddHandler DevExpress.Data.Utils.ProcessStartPolicy.Failed, AddressOf ProcessStartPolicy_Failed  
        Application.EnableVisualStyles()  
        Application.SetCompatibleTextRenderingDefault(False)  
        Application.Run(New Form1)  
    End Sub  

    Private Shared Sub ProcessStartPolicy_Failed(ByVal sender As Object, ByVal e As DevExpress.Data.Utils.ProcessStartPolicy.ProcessStartFailedExceptionEventArgs)  
        If TypeOf e.Exception Is Win32Exception Then  
            Dim si As System.Diagnostics.ProcessStartInfo = TryCast(sender, System.Diagnostics.ProcessStartInfo)  
            e.Throw = False  
            MessageBox.Show("File not found: " & si.FileName)  
        End If  
    End Sub  
End Class