如何将所有用户安装的应用程序加载到gridview中，并使它们在android中可单击

I am making an android launcher, and i need to know how i can load all the apps into a gridview. I want system stuff like calculator and all of that to show up as well. How can i do that? I have search for a long time now without any solution. Please help me and thanks very much!I am making an android launcher, and i need to