(Perfect implementation of QQ login pull down account switching, and use SharePreference to save user information. There are user-defined database operation classes in the program, which can be imitated in the project of various demand databases. The drop-down box is implemented using PopupWindow. In addition, a user-defined BaseAdapter is included to imitate a ListViewItem that can implement arbitrary interfaces. And the algorithm including login information verification is actually a small algorithm, just to show that the program is small and has all the five internal organs. However, there are a few minor problems in the program that are not managed. Because Sharereference has limitations in saving information, when there are many accounts that may be deleted, the management is not very good. However, it is not a big problem. It can be optimized with a little correction. I think it is better to use Database to store data, so I haven't improved it. However, the overall program is still very complete. Here is another better way to save user information with SQLDatabase. Link:/data/922286)