Debugging VB .NET Applications

Whatever your project might be, debugging the application always helps you identify the cause of errors/bugs and helps you fix them. You might be working on a Strategic (new) project or Tactical (existing) project, debugging always comes handy. A simple scenario could be a project where the code was already written by other developers and you are finding it difficult to fix bugs. An example can be a huge windows application where on one of the forms you are clicking a button and this button might save a message along with the current system time. When you click this button you are able to save a message but recording a wrong time. In such a scenario you are suppossed to follow the debugging procedures and set breakpoints to find the code error. In this case you need to set a breakpoint at button_save event and press F11 to see the flow of the program and fix the bug. To understand debugging we will follow a simple example.

Here, we will work with a sample application to understand debgging. Open a new Windows Form and place 2 buttons, 2 labels, a datetimepicker control and 2 text boxes. The form in design mode should like like the image below.

The codebehind for this form is as follows:

Public Class Form1 Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)_ Handles MyBase.Load TextBox2.Text = DateTimePicker1.Value.Date End Sub Private Sub getTxt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)_ Handles getTxt.Click TextBox1.Text = "Debugging Test" End Sub Private Sub clr_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)_ Handles clr.Click TextBox1.Text = " " TextBox2.Text = " " End Sub End Class

For the code listed above we will set a breakpoint at the clr_click event of the clear button in the code editor window. To set a breakpoint, point the mouse pointer towards the left of code and click it to see a red circle as shown in the image below.

Once you set the breakpoint, run the application by hitting F5. Current system date loads into textbox2. Click the get text button to fill textbox1 with text. Now, click the clear button to clear both the textboxes. Once you click the clear button, control shifts to the code editor, highlights the click event of the clear button with a yellow background and looks like the image below.

Now, when you place the mouse pointer on Textbox1.Text it shows the current value textbox1 is holding in it's text property which is "Debugging Text". Similarly, textbox2 shows the curent date when you place the mouse pointer on TextBox2.Text. Now, press the F11 (Step Into) key to see the control flow. The control shifts to TextBox1 and it still shows the text Debugging Test. Press F11 again and now the control shifts to TextBox2. Now, if you place the mouse pointer on TextBox1.Text it shows that the text property is set to null which means that the control has set the text property of TextBox1 to null. The image below shows that.

At this point, textbox2 still holds the current system date. Press F11 again and now the control shifts from textbox2 to End Sub. Now, if you place the mouse pointer on TextBox2.Text it shows it's text property as null. If you press F11 once again the control finishes End Sub and jumps back to the form which is running. What we saw now is the passing of program flow when we set breakpoints and how the values change in the block while the control executes line by line.

With the above example we understood how debugging can help us find and fix errors. This was a small example but in real time applications it will be very helpful in finding and fixing some hard to find bugs. In a huge windows application there may be many forms and many of those forms might get inherited by other forms in a different solution or a different project in the same solution. Setting breakpoints at certain points on the form and running the application will help you to get to know how the program control flows, what method on one form is calling on another form and so on and helps you understand the logic n fix errors.