Solution to "Cannot modify item collection after setting DataSource property" in C# ComboBox control

When using the ComboBox control, I encountered a problem with rebinding assignment. Under normal circumstances, when reassigning data or binding data sources, in order to prevent problems from occurring in data, the original data will be cleared first, so I just wrote it like this, but it didn't quite happen if I wrote it like this. So I looked it online. I found that someone did this. Inspiration suddenly appears, and when you clear the drop-down list item, the empty value will be "null", and the problem will be solved.

 if (combo_Area. > 0)
      {
        combo_Area.DataSource = null;
        combo_Area.();
      }

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