How to use Dialog in Dynamics Ax.

If you came accross a requirement , where you need to collect the information and then executes a task . In such scenario Please make use of RunBase class.
Advantage of RunBase class
1. It provides dialog for presenting and collecting the information from user.
2. Pack/Unpack methods , for storing the last value entered by the user.
3. Progress bar ,for long time process where in you can show a progress bar.
4. Validate method , to validate the data entered by the user in the dialog.

you can refer tutorial in AOT->Classes->tutorial_RunBaseForm .