解決方法：去掉“Enable Instant run to host swap code/resource changes on deploy(default enabled)”的勾選項
Settings→Build→Instant Run:
1：Enable Instant Run to hot swap code/resource changes on deploy (default enabled)
//啟用即時運行 熱交換代碼/資源變化 部署(默認啟用)
2：Restart activity on code changes
//當代碼變動時重啟
3：Show toasts in the running app when changes are applied
//當代碼變動應用時彈出toast
4：show Instant Run status notifications
//在notification里顯示instant Run 的狀態
當再次勾選后出現了新問題
The APK file D:\Android\del\MaterialDemo\app\build\outputs\apk\app-debug.apk does not exist on disk.
Error while Installing APK
解決方案：build-->build apk