Getdlgitem () returns NULL.

When getdlgitem () is used as follows, null is returned: (the ID of this dialog box is idd_simp_arrow_property)
Cwnd * pbox = getdlgitem (idc_simp_arrow_style );

Cause:
The idd_simp_arrow_property in the resource. h file of Project 1 is defined as follows:
# Define idd_simp_arrow_property 2053

In the resource. h file of another project, another control is defined as 2053.
# Define idd_dialog_acttool 2053

The two projects belong to the same solution. Therefore, the returned value of getdlgitem is null because of the definition conflict. The modification is as follows:
# Define idd_simp_arrow_property 2055
Solved