Please explain the statement...

Please demonstrate, add explanation, preferably add some sample codes to illustrate the following statements. I am trying to fully understand the point the author of A, B, and C below is making. Each of these statements most likely true but I am not quite getting them:

A) Never use form or class level variable scope (or access level) unless it is needed.

B) In this code, if the variable strShowMessage is declared as String then that is incorrect since the Messagebox.show does not return String but a DialogResult type:
  If strShowMessage = Windows.Forms.DialogResult.Yes Then

C) “textbook text changed event handler that assigns the textbook content to a local variable” is indeed useless.
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Mike EghtebasDatabase and Application DeveloperAsked:
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David Johnson, CD, MVPOwnerCommented:
A) Never use form or class level variable scope (or access level) unless it is needed.

These are global variables and as such can be a real pain to debug as you will not know which function or class changed the variable. It also makes it extremely hard to maintain the code as a change in 1 function will affect every other function that uses that variable.

Keeping your variables local to a function and only passing in required variables and only returning another variable then you know exactly where the variable changed and why.

Ergo, never use global variables unless you absolutely have to.

B) strShowMessage is declared as String
Windows.Forms.DialogResult.Yes is an enum not a string,
http://msdn.microsoft.com/en-us/library/system.windows.forms.dialogresult.aspx#Y114

C) “textbook text changed event handler that assigns the textbook content to a local variable” is indeed useless.


when the text changed event handler fires if you simply copy the content to a local variable, then you're going to have the event fire for every change in the textbox. wait for the user to finish entering the data, you can use this to validate data i.e. restrict the data to say numeric or alphabetic characters but it will be firing very often, wait until the user is finished.
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Mike EghtebasDatabase and Application DeveloperAuthor Commented:
Thank you
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