IFRAME runat = server dynamically add SRC

I encountered such a problem recently when I was doing something. I used a fixed height at the beginning, but the page with few content is really ugly. Today I am determined to change it to adaptive. Baidu has been searched almost all over. I have also found several posts with the same questions as I have. None of them can solve the problem. Finally, a friend gave me a prompt, to solve this problem.
The method is simple, but it is hard to think. I want to help people who have the same problems with me.
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In this method, I have to remove ruant = "server.
Some people may want to remove it and they will not be able to control the SRC of IFRAME in the background. Haha! Rest assured!
Add src = "<% = geturl () %>" to the IFRAME tag"Does this solve the problem of background control?