When I added the appcompat-v7 library to my android project, r.java was deleted

After adding the library appcompat-v7 to my application, r.java is deleted and the console displays the following error:

In fact, I'm using Android: theme. Light (the default theme of Android). I want to use appcompat theme instead of Android's default theme. And in java files, I want to extend appcompatactivity instead of activity to give some substantive appearance to my application action bar

But the problem is that when I import the appcompat-v7 library into my project, r.java is deleted. So I can't do anything

Note: when I create a new project, when I import the appcompat-v7 library, it will not give any error messages and will work normally

I want to make some suggestions on how to change the current theme, so please make some suggestions from where I should start this work

My project configuration:

    android:minSdkVersion="17"
    android:targetSdkVersion="21" 

I have tried to clean up and rebuild the project

resolvent:

This problem mainly occurs in eclipse. Now, most people are using Android studio. Therefore, just delete the build folder or clean up the project. It will work normally