C# uses LINQ, generics, and Index functions to optimize switch (or multiple if) statements

Background:
Determine whether a variable is in a certain format in ".txt.doc.xls.ppt.pdf", and if so, perform the corresponding operation.

Method 1: Use generics

readonly IList<String> fNames = new List<String>() {
             ".doc",
             ".txt",
             ".xls",
             ".ppt",
             ".pdf"
        };
private void Test(string fName)
{ 
    if(fNames.Contains(fName))
	{
        MessageBox.Show(fName);
    }
}

Method 2: Use LINQ

private void Test(string fName)
{
    if (new string[] { ".doc", ".txt", ".xls" }.Any(x => fName == x))
    {
        MessageBox.Show(fName);
    }
}

If it is &&, use All

knowledge Extension:

LINQ query syntax

Lambda expression expression tree

Simple usage example of LINQ query

Method 3: Use Index function

private void Test(string fName)
{
    string str = ".txt.doc.xls.ppt.pdf";
    if (str.IndexOf(fName) >= 0)
    {
        MessageBox.Show(fName);
    }
}

C# IndexOf Usage

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