Delphi Prism Empty String Check

In Prism, a string can be nil (unassigned), assigned an empty string (""), or assigned a value.  Therefore, to check if a string is empty, you have to check against both nil and (""). Alternatively, you can check the length of the string or use String.IsNullOrEmpty.

Using IsNullOrEmpty

The .NET framework provides a IsNullOrEmpty static method as part of the String class. Remember, the syntax to use a static method is always ClassName.MethodName and you do not have to create the class ahead of time because it is static.

var s: String;

//Unassigned check.
If String.IsNullOrEmpty(s) then
  MessageBox.Show("empty or null string");

//Assigned a non-zero value.
s := "health care reform";

If Not String.IsNullOrEmpty(s) then
  MessageBox.Show("string contains a non zero value");

//Empty string.
s := "";

If String.IsNullOrEmpty(s) then
  MessageBox.Show("empty or null string");