Not Able To Debug App In Android Studio

I solved this issue after doing the following steps:

Go to Tools==>android==>Disable ADB integration and enable it again.

After that, unplug USB from device and plug in again.

Finally press shift + F9

There is a Debug icon on the toolbar. It looks like a little "bug" and is located right next to the Run icon (which looks like a play button). Try launching the application with that.

Edit: The following is deprecated when using Android Studio with Gradle.

There is also a debug flag in the AndroidManifest.xml file. It is located under the application tag, and should be set to "true", as follows:

<application android:debuggable="true">
</application>

Another thing to be careful of (I did this so I know, duh). Be sure not to enable Proguard for debug!