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The source code in this issue is designed for Visual Basic 4.0 and higher. Similiar techniques can be used for Visual Basic 3.0, it would just need to be converted to a regular BAS module. If anyone is interested in VB 3.0 source code, please contact us. We don't currently have it available, but if we get enough requests we will convert it.
In this issue we are going to implement a gauge control without requiring the gauge control VBX or OCX. This will avoid having to ship yet another control with your application. It also provides some better error checking and some features to improve performance.
This class is a replacement for the standard Gauge VBX/OCX included in Visual Basic. It allows you to show a gauge or meter bar to indicate the progress of a particular task. The uniqueness of this class is that it uses a standard Picture Control.
All you do to use this class is drop a Picture Control on your form and resize it to the size you want. Create an instance of the class, define a couple of properties and execute your task. During your task you need to call the Current property to assign the current value to the gauge. Assigning this property will automatically update the control to show how close to completion the task is.
This class works by using the Line method to draw a box on the picture control to simulate a gauge. The Refresh method is the one that does all the work. A good exercise would be to modify it to work vertically as well as horizontally (which is the default method). If anyone implements this and would like to share it with the rest of our subscribers, let us know.
This UpdateInterval feature is really only important for when you have many steps (over 50 or so). Every screen refresh of the gauge takes a significant amount of CPU cycles (time). The more you refresh the control, the greater the overhead the gauge. Depending on the task, you can implement a gauge that will take more time to update than the entire process takes to run.
An example of a case like this would be a calculation loop that was able to be done completely in memory. If each iteration of the loop occurs very fast and you update the gauge on each iteration, it is likely that using the gauge will increase the total time to complete the calculation significantly. The UpdateInterval forces the gauge to only update every x times the Current property is incremented. Let's say you have a task that has 1000 steps. By default the UpdateInterval will be set to 10. This means the gauge will only update when Current is equal to 10, 20, 30, 40, and so on. Instead of updating the gauge 1000 times the cGauge class will only update it 100 times, which will save LOTS of CPU cycles.
This sample assumes you have a form that has a picture control on it called pictGauge.
Dim oGauge as New cGauge oGauge.QuickStart pictGauge, 0, 100 For x = 0 to 100 ... Do something ... oGauge.Current = x Next
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That concludes this issue of COTW. We hope you find the source code useful in your development.
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