Category: Vb6 doevents

Vb6 doevents

Vb6 doevents

The following code example demonstrates using the DoEvents method. When the example runs, a user can select graphics files from an OpenFileDialog. The selected files are displayed in the form. The DoEvents method forces a repaint of the form for each graphics file opened. In Visual Studio, if you add an OpenFileDialog to your form by using a drag operation, you will have to modify the following InitializeOpenFileDialog method by removing the line that creates a new instance of OpenFileDialog.

The example also requires that the Control. Click event of the Button control and the FileOk event of the OpenFileDialog are connected to the event handlers defined in the example. When the example is running, display the dialog box by clicking the button. When you run a Windows Form, it creates the new form, which then waits for events to handle.

Each time the form handles an event, it processes all the code associated with that event. All other events wait in the queue. While your code handles the event, your application does not respond. For example, the window does not repaint if another window is dragged on top. If you call DoEvents in your code, your application can handle the other events.

vb6 doevents

For example, if you have a form that adds data to a ListBox and add DoEvents to your code, your form repaints when another window is dragged over it. If you remove DoEvents from your code, your form will not repaint until the click event handler of the button is finished executing.

For more information on messaging, see User Input in Windows Forms. Unlike Visual Basic 6. Sleep method. Calling this method causes the current thread to be suspended while all waiting window messages are processed.

If a message causes an event to be triggered, then other areas of your application code may execute. This can cause your application to exhibit unexpected behaviors that are difficult to debug. If you perform operations or computations that take a long time, it is often preferable to perform those operations on a new thread. Skip to main content. Exit focus mode. Forms Assembly: System. Processes all Windows messages currently in the message queue.

Caution Calling this method causes the current thread to be suspended while all waiting window messages are processed. Is this page helpful? Yes No.The VBA DoEvents function temporarily pauses a running macro, giving Excel a chance to process key presses, mouse clicks, and other operating system messages. In long-running macros, Excel can appear to hang and become unresponsive, and the macro may be impossible to interrupt. If DoEvents is included in your code, users can be assured that the macro is still running, and can still interrupt execution if necessary.

If a lot of complex and demanding functions were being performed inside this loop though, Excel would take longer to register a key press event — up to several minutes or possibly not at all, especially if the computer is running other programs at the same time. DoEvents is called every time through the loop, which ensures that the macro is always yielding execution so that Excel can process any messages sent to it.

Take a second look, though. Another danger is that DoEvents can serve as a window for other macros to run inside of. Toggle off Design Mode in Excel, then run the Test macro you added earlier. While the Test macro is running, you can click the CommandButton on the worksheet, and its associated macro will run as soon as DoEvents gives the Test macro a break.

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The danger here is if the CommandButton macro altered the data the Test macro was working on, or triggered the Test macro again. Finally, you should be aware that DoEvents will cause your macro to suffer a performance impact when called.

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Inside a loop, this impact will add up quickly unless you limit how often DoEvents is called. Referring to our Test example, try this:.

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Despite these dangers, DoEvents is a handy function that aids in testing and debugging. Consider adding DoEvents to long-running loops. Another reason to include DoEvents is to allow for user feedback.

Without DoEvents, Excel may not receive the messages to repaint the UserForm, giving a user the impression that the macro has stopped working — especially if you switch to another program and then try to switch back to Excel. VBA DoEvents.

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Associated Files Download Links. Public Sub Test. Dim i As Long. Next i. End Sub. Range "A1".

vb6 doevents

Dim c As Range. Next c. You may also like some of this related content Contact Us. Automate Excel.A large amount of VBA code is required when the requirement is huge. In those cases excel hangs and stops for some time and even sometimes it becomes unresponsive. The above code will insert serial numbers from 1 to It will easily take more than a minute to execute the task. During the execution, excel hangs for a considerable amount of time to complete the task.

Moreover, we cannot access the worksheet we are working on. This is a frustrating thing, then how do we make the excel worksheet to be available to work while the code is running behind the screen.

When the code is running behind the screen we can add rows, column, and delete the same, we can rename the sheet and we can do many other things as well.

vb6 doevents

The moment we add DoEvents it makes the vba code run fast and allows us to fell that the mentioned task is running for itself. Here we learn how and when to use DoEvents function in Excel VBA with the help of an example and downloadable excel sheet. You can learn more from the following articles —. Your email address will not be published.

Save my name, email, and website in this browser for the next time I comment. Login details for this Free course will be emailed to you. Free Excel Course. DoEvents function passes control to the operating system of the computer we are working on. How to use DoEvents Function? Popular Course in this category. View Course. Note : Despite the above dangers of DoEvents, it is still a handy function. We can use DoEvents as part of the debugging process when we try to fix bugs of the code we have written.

Leave a Reply Cancel reply Your email address will not be published.In our Microsoft Access, VBA, and VB6 programs, we often need to pause processing for a certain period of time, or until a specific time, and then continue processing. One common way to do this is to use the DoEvents function in a loop while waiting, like this:. DoEvents releases time to other processes on the computer.

However, this method consumes almost all the CPU time and slows down the PC considerably because there's no pause in the processing. As soon as the DoEvents command executes, it executes again and repeats as fast as the PC can run. It literally consumes all the available CPU cycles, only giving time to other processes during the tiny period DoEvents is executing.

This is a significant problem when pausing for more than a few seconds to wait for the user to perform other tasks. Users will experience the entire PC slowing down. You can see the impact of this by looking at the Performance tab of the Windows Task Manager:. The proper approach is to use the Windows Sleep command which lets you wait but releases CPU cycles to the computer.

To use the Windows Sleep command, you must first add the following Declare statement to the Declarations section of your module:. Now you can can call the Sleep command to pause, while keeping the system resources free. For instance, this code uses the Sleep command to wait the specified number of seconds before continuing processing:.

This code uses the Sleep command to wait until the specific time to continue processing:. This code and much more is available in Total Visual SourceBook. All Our Microsoft Access Products. Reader Choice. PDF Fact Sheet. Celebrating our 33rd Year of Software Excellence. Vienna, Virginia Privacy Policy Webmaster.

Video 38: VB 6 Programming, WithEvents In A Class Module, Copy Events From Controls

Toggle navigation. Products Microsoft Access Products. All Microsoft Access Products. Total Access Admin. Total Visual Agent.DoEvents returns zero in all other applications. DoEvents passes control to the operating system. Control is returned after the operating system has finished processing the events in its queue and all keys in the SendKeys queue have been sent.

DoEvents is most useful for simple things like allowing a user to cancel a process after it has started, for example a search for a file. For long-running processes, yielding the processor is better accomplished by using a Timer or delegating the task to an ActiveX EXE component.

In the latter case, the task can continue completely independent of your application, and the operating system takes care of multitasking and time slicing. Any time you temporarily yield the processor within an event procedure, make sure the procedure is not executed again from a different part of your code before the first call returns; this could cause unpredictable results.

In addition, do not use DoEvents if other applications could possibly interact with your procedure in unforeseen ways during the time you have yielded control. This example uses the DoEvents function to cause execution to yield to the operating system once every iterations of the loop. DoEvents returns the number of open Visual Basic forms, but only when the host application is Visual Basic.

Have questions or feedback about Office VBA or this documentation? Please see Office VBA support and feedback for guidance about the ways you can receive support and provide feedback. Skip to main content. Exit focus mode. Example This example uses the DoEvents function to cause execution to yield to the operating system once every iterations of the loop.

End If Next I ' Increment loop counter. Related Articles Is this page helpful? Yes No. Any additional feedback?

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Avoid Using DoEvents to Wait in Microsoft Access, VBA, and VB6

Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. What does "DoEvents" do in vb6? Why do I get the error message "Out of stack space"? What does it mean? The reason you get an out of stack space error is probably because DoEvents is allowing events to occur that call your code again, which again calls DoEventsand so on until the stack space, which tracks the return addresses for all these calls, has run out.

In general, I do not recommend using DoEvents due to problems like these and the fact that it violates the overall event-driven design of Windows. A slightly different way of looking at DoEvents is that it flushes the events in the event queue. DoEvents says to run that event handler sub now, instead of waiting till the end of your sub.

While I agree in spirit with Jonathon about not using DoEvents, I would temper his statement by saying I only recommend using it if you know exactly why, and know all of the repercussions of changing the order of the event queue this way. Most often, DoEvents is indicated when you want to update your screen in some way from within the context of a subroutine, before the subroutine is finished executing. An example of this is when you are using the ProgressBar control.

Suppose you are iterating through several thousand records, and want to provide feedback to the user as to how far along you are by updating a progress bar. You might interrupt your loop every hundred records and change the value on the progressbar control.

However unless you do something about it you won't see the change on the screen until after the progressbar's change event handler runs, and that handler won't run until your sub is done executing. It will just get put in the event queue.

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The way to force the change event to run immediately, suspending your sub, is to call DoEvents. This will flush all existing events from the queue--in this case your progressbar's change event--and will update the progressbar control on the screen.

Now, "out of stack space" basically means that you've been caught in an endless loop of function calls.A Developer.

An Eweek. VB6 2D Sprite control To live is difficult, but we do it. As you may know, this keyword yields operation to the operating system so that it can process other events. Many times after initiating a procedure, you may want to pause execution to gather further information from an end user via a form. For example, consider a project with two forms.

The main form performs a calculation and displays the results. The second form lets an end user manually enter two numbers for the calculation. When you click the second form's Submit button, the main form multiplies the user-entered numbers and displays the results. Typically, to handle this feature, you might use DoEvents to wait until the user has entered the two numbers. It allows the system to take care of other things while you are in the loop.

If you don't put a DoEvent in a loop, especially a lengthy loop nothing else can take place until the loop ends.

VBA DoEvents

What do you think will happen if you get stuck in a loop and your loop does not have a DoEvents in it? You can't get out of the loop unless you kill the program. So by putting a DoEvent in that loop you could add a button that will allow you to either break out of the loop or examine what is taking place. Without the DoEvent the button or any other control is useless until the loop ends. If you are running a long loop like perhaps reading 10, records from a database or something like that without the doevents then form repaints and such will not happen plus the program will not respond to windows messages and the UI will appear to be frozen.

You may also get a not responding message on the title bar or in task manager even though the program is still working fine.

If you switch to another program and back during such a process you may not see your program at all until either it hits a doevents or completes the loop. On the downside if you have a timer running or a Winsock or Com control when a doevents is hit the code may jump to the sub for one of those events and start executing even though that is not what you may want to happen.

So again they must be used wisely. Often you can over come potential display issues by using a call to refresh rather than doevents without the other side effects. Width, Extender. Height TransparentAlphaBlend Picture1. Height, CInt lngOpacyPicture1. Point 0, 0 UserControl. Image UserControl.

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