FIX: GDI Resource Leak Using Checkboxes in ListView Control

1. Open a new Standard EXE project. Form1 is generated by default.
2. From the Project menu, choose Components, select "Microsoft Windows Common Controls 6.0" and click OK.
3. Add a second form (Form2) to the project.
4. Add a ListView control (ListView1) to Form2. Leave the Checkboxes property for the control set to the default of False.
5. Add the following code to Form2's Activate Event:

   Private Sub Form_Activate()
       ' Set the ListView's checkboxes property to True.
       ListView1.Checkboxes = True
       
       ' Do any initialization of the ListView here.
       With ListView1
           .ListItems.Add , , "Item 1"
           .ListItems.Add , , "Item 2"
       End With 
   End Sub
   					

6. Add the following code to Form2's QueryUnload event:

   Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
       ' Set the checkboxes property
       ' of the listview to False.
       ListView1.Checkboxes = False
   End Sub
   					

7. Add a CommandButton (Command1) to Form1. Add the following code to Form1's code window:

   	Private Sub Command1_Click()
       		Dim f As Form2
     		Dim i As Long
     		For i = 0 To 100
       			Set f = New Form2
       			f.Show
       			Unload f
       			DoEvents
       			Set f = Nothing
     		Next i
   	End Sub
   					

8. Start a program to monitor system resources as follows:
   • Windows NT: Enter CTRL+ALT+DEL, and click Task Manager. Select the Performance tab.
   • Windows 95/98/Me: Start the System Monitor tool, which is located in the System Tools folder in the Accessories folder. If the System Monitor tool is not available, it can be installed from the Control Panel using the Add/Remove Programs option. On the Edit menu, click Add Item. Click the Memory Manager Category, click the Allocated Memory Item, and click OK.
   
   
9. Run the project and click on the Command1 button on Form1. Notice the resource usage.Result: Excessive resource use doesn't occur.

Back to the top

Steps to Reproduce Behavior

1. Open a new Standard EXE project. Form1 is generated by default.
2. From the Project menu, choose Components, check "Microsoft Windows Common Controls 6.0," and click OK.
3. Add a second form (Form2) to the project.
4. Add a ListView control (ListView1) to Form2 and set its Checkboxes property to True.
5. Add a CommandButton control (Command1) to Form1 and paste the following code into Form1's code window:

   	Private Sub Command1_Click()
       		Dim f As Form2
     		Dim i As Long
     		For i = 0 To 100
       			Set f = New Form2
       			f.Show
       			Unload f
       			DoEvents
       			Set f = Nothing
     		Next i
   	End Sub
   					

6. Start a program to monitor system resources as follows:
   • Windows NT: Enter CTRL+ALT+DEL and click Task Manager. Select the Performance tab.
   • Windows 95/98/Me: Start the System Monitor tool, which is located in the System Tools folder in the Accessories folder. If the System Monitor tool is not available, it can be installed from the Control Panel using the Add/Remove Programs option. On the Edit menu, click Add Item. Click the Memory Manager Category, click the Allocated Memory Item, and click OK.
   
   
7. Run the project. Click on the Command1 button on Form1. On NT, you should watch as the memory used by the process climbs continuously while running the program, and is only cleaned up when exiting Visual Basic or the compiled program.Result: Excessive resource use.

Back to the top