How to Show/Hide Colums in an oracle report at runtime

I have build a report. but now i want that the user of the report can make the unnecessary columns invisible from the report at runtime and next time when he opens the report that invisible colums should not be visible to him. but when he needs, he could make that colum visible.

From the column's property; you can use "Format Trigger" to code your conditions that you need either to show that column (Return (true) ) or hide it (Return (False)). 
Hope that helps;

Solution:
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Create a user parameter field in the report, let user to select in parameter form, for example in the field named "show_hide" user can have options 
1: Show Column 
2: Hide Column 
Create a format trigger for the column(s) which you desired to show/hide, 
enter the following code 
if :show_hide='1' then 
return (TRUE); 
else 
return (FALSE); 
end if; 

Thats it.