Drop down menu in Custom Editor

Questions & Answers
1

If I wanna create a drop down menu, how should I do that?

Please help~~~

2

Use an EditorGUI.Popup field.

http://unity3d.com/support/documentation/ScriptReference/EditorGUILayout.Popup.html

You may also find EditorGUI.Foldout useful.

3

Popup field example

int selected = 0;
string[] options = new string[]
{
    "Option1", "Option2", "Option3", 
};
selected = EditorGUILayout.Popup("Label", selected, options);
4

Its a bit old topic, but maybe someone still loking for another answer.
If you look for a simple solution for dropowns based on enums:

5

Try using the new asset Dropdown Attribute

you can make the dropdown without creating a custom editor

string[] options = new string[]
 {
     "Option1", "Option2", "Option3", 
 };
[Dropdown("options")]
string selected;