如何使用Delphi7进入RTL/VCL

Make sure you have the "Use debug dcus" option enabled in the Project Options, and the VCL source folder is in the Debugger's Source path.

As for why you cannot assign a TJPEGImage to a TJPEGImage, that would normally only happen if you are trying to pass a TJPEGImage object across a DLL boundary without the use of runtime packages, thus the app and DLL are doing internal comparisons against different copies of the RTL, causing the is 操作员(即: ASource is TJPEGImage )在通常报告为“真”的情况下返回“假”。

Did you added the RTL/VCL source path to debug units path? Also, my Delphi 7 asks me to provide location of source file I want to step into if it's not in the path ... so should yours do :)