Using the Graphical Control Objects I realized that CListView and CComboBox open under other objects, like the following picture.
this issue has been posted again in the forum ( https://www.mql5.com/en/forum/6822 ), but no one replied.
Is it any solution or is a bug o mql4/mql5 ?
You can solve the problem by drawing the objects from the most bottom one, then draw the upper one and upper.
The downside of combobox is it doesn't have any scroll bar when the items number more than available chart's space.