Not able to connect adb after upgrate Android Studio to 3.4

Replace your platform-tools with this one and delete the other one. https://dl.google.com/android/repository/platform-tools_r26.0.0-windows.zip

I was also facing this issue in android Studio 3.4 version, but now I have fixed it , if you are using windows then follow these steps:

1. Download Platform tools from here https://dl.google.com/android/repository/platform-tools_r26.0.0-windows.zip

2. Extract downloaded zip file

3. Go To location "C:\Users\your_computer_user_name\AppData\Local\Android\Sdk" and Delete "Platform tools" folder

4. Copy and Paste, downloaded platform tool folder to above location

5. Now Go to your android studio and Rebuild your project Then run.