Revert "Revert "Update MainActivity.java""

This reverts commit 2eaec9cd03773e01fce63fd4b945c89af315e43d.
Revert "Update MainActivity.java"

This reverts commit 9ef9ba756523df76e443567fb4c2148bb779ea2b.
试着张的
Revert "试着张的"

This reverts commit c45bac7ee52885e9c75fc93e66e2c46f347e5c5c.