Sybex - Mastering Visual Basic .NET VB NET Functions (VBL).pdf下载

Bonus Reference VB.NET Functions and Statements This bonus reference describesthe functions and statements that are supported by Visual Basic .NET, grouped by category. When you’re searching for the statement to open a file, you probably want to locate all file I/O commands in one place. This is exactly how this reference is organized. Moreover, by grouping all related functions and statements in one place, I can present examples that combine more than one function or statement. The majority of the functions are the same as in VB6. One difference is that many of the VB6 statements are implemented as functions in VB.NET. Moreover, many VB6 functions have an equivalent method in a Framework class. VB programmers are so accustomed to the old func- tions that they will not consider the alternatives—at least for a while. The Len() function of VB6 returns the length of a string. In VB.NET you can retrieve the length of a string with the Length method of a string variable. If strVaris declared as string variable, you can retrieve its length by calling the Length method: Dim strVar As String = “a short string” Console.WriteLine(“The string contains “ & strVar.Length & “ characters”) Or you can call the Len() function passing the name of the string as argument: Dim strVar As String = “a short string” Console.WriteLine(“The string contains “ & Len(strVar) & “ characters”) Most of the built-in functions are VB6 functions, and they accept optional arguments. VB.NET uses overloaded forms of the same function, and this is an important difference you have to keep in mind as you work with the built-in functions. If you omit an optional argument, you must still insert the comma to indicate that an argument is missing. Optional arguments are enclosed in square brackets. The Mid() function, for example, extracts a number of characters from a string, and its syntax is newString = Mid(string[, start][, length]) The starting location of the characters to be extracted is specified by the startargument, and the number of characters to be extracted is length. If you omit the startargument, the extraction starts with the first character in the string. If you omit the lengthargument, all the characters from the specified position to the end of the string are extracted. The only mandatory argument is the first one, which is the string from which the characters will be extracted, and this argument can’t be omitted. The methods of the various classes are discussed in detail in the book. This bonus reference con- tains all the functions supported by VB.NET, and these functions are listed by category in Table 1. Items in the table that are not followed by parentheses are statements and are also described in this reference.