R.java is very important in android application development. It is used to identify all resources data such as id, layout, image, drawable resource etc. R.java is generated by android studio automatically. But it is sometime confused for developer to use it. This article will help you to resolve these problems about R.java you may encounter.
1. Where R.java Saved At ?
R.java is commonly saved at directory like
You can also find it in android studio project view list like below.
2. Why Can Not Find R Class In Android Studio ?
This is commonly because you select wrong sub view in project view. You can change project view’s sub view as following.
- Click ” View —> Tool Windows —> Project ” menu item in top menu bar.
- Above action will show project view in left panel. At left top in project view, there is a drop down list where you can choose project view’s sub view.
- Choose Project in sub view drop down list, then you can see all the folders under current project will be listed at below panel. You can find the R class in the directory tree also. If you choose other sub view, it will display different content of that sub view.
3. What Data Saved In R.java ?
Double click R.java file, it will display it’s content in right panel. The source code include a lot of int type variables, each int variable refer to one resource in current android application.
You can find there are some inner public static final classes defined in R.java also , each inner class represent one kind of resource such as id, layout, string, color, drawable etc.
You do not need to care about those int variable and their values. And do not edit them also. If you change the value, you may encounter some strange error when build android project.
4. How To Resolve Package R Dose Not Exist Error ?
Sometimes you may encounter strange errors about R.class. Such as package R dost not exist, R can not be resolved as a type. You can fix these errors follow below steps.
- Click ” Build —> Clean Project ” or ” Build —> Rebuild Project ” in top menu bar in android studio. This will let android studio regenerate R.java again. It will clean the cache and include all new added resources.
- If above method still do not take effect, you should check your AndroidManifest.xml file carefully. You need to make sure that the package value in AndroidManifest.xml root xml element match your activity package.
In above picture, the manifest root xml element’s package value is com.dev2qa.example, and the launcher activity class is in package com.dev2qa.example.image. So change the package value, the error is resolved.
- If the error still exist, you should check AndroidManifest.xml carefully to find the potential code that may generate the error. Or you can restart android studio or even computer 🙂