I've read Variable Sidebar Content Example in http://codex.wordpress.org/Conditional_Tags anh try to follow it. So I wrote these code in sidebar.php:
echo 'This is Single!';
echo 'This is home!';
echo 'This is category!';
echo 'This is not single!';
Then, when I was in home page, it showed "This is Home" (correct), But when I viewed catagory page, it showed "This is Home" (incorrect) and when I viewed single post, it still showed "This is Home" (incorrect).
What's the problem? And how to solve this?