"id cannot be resolved or is not a field" error?

I keep getting this error. Should I just make id a field?

My code is:

public void onC开发者_如何学JAVAreate(Bundle icicle) 
{
    super.onCreate(icicle);
    setContentView(R.layout.main);
    ImageView mainimage = (ImageView) findViewById(R.id.mainanim);
    mainimage.setBackgroundResource(R.anim.mainanim);
    mainanimation = (AnimationDrawable) mainimage.getBackground();
}

How exactly do you fix this?

Look at your import statements at the top. If you are saying import android.R, then there that is a problem. It might not be the only one as these 'R' errors can be tricky, but it would definitely definitely at least part of the problem.

If that doesn't fix it, make sure your eclipse plugin(ADT) and your android SDK are fully up to date, remove the project from the emulator/phone by manually deleting it from the OS, and clean the project (Launch Eclipse->Project->Clean...). Sounds silly to make sure your stuff is fully up to date, but the earlier versions of the ADT and SDK has a lot of annoying bugs related to the R files that have since been cleared up.

Just FYI, the stuff that shows up in the R class is generated from the stuff in your project res (aka resources) folder. The R class allows you to reference a resource (such as an image or a string) without having to do file operations all over the place. It does other stuff too, but that's for another answer. Android OS uses a similar scheme - it has a resources folder and the class android.R is the way to access stuff in the android resources folder. The problem arises when in a single class you are using both your own resources, and standard android resources. Normally you can say import at the top, and then reference a class just using the last bit of the name (for example, import java.util.List allows you to just write List in your class and the compiler knows you mean java.util.List). When you need to use two classes that are named the same thing, as is the case with the auto-generated R class, then you can import one of them and you have to fully qualify the other one whenever you want to mean it. Typically I import the R file for my project, and then just say android.R.whatever when I want an android resource.

Also, to reiterate Andy, don't modify the R file automatically. That's not how it's meant to be used.

Do not modify the R class. The error means there's something syntactically wrong with your XML layouts and R cannot be auto-generated. Try looking there and post the xml code you're not sure about, if any.

Edit : also: remove "import android.R" from imports at top of file (if there)

One possible solution:-

Summary: make sure you are using import com.yourpkgdomainname.yourpkgappname.R instead of import android.R

Details: The problem occured when I changed ID of a label which was being referred in other places in the layout XML file. Due to this error, the R file stopped generating at first. Eclipse is bad in handling errors with the layout files.

When I corrected the ID reference (with project clean few times and Eclipse restarts, I noticed that my import packages now has:
import android.R

Changing it to following fixed the error:
import com.example.app.R

I just fixed my problem right-clicking in the layout folder and clicking in the option Validate. Some windows will appear, you just clik OK and ist fine.

May be you created a new xml file in Layout Directory that file name containing a Capital Letter which is not allowed in xml file under Layout Directory.

Hope this help.

Just throwing this out there, but try retyping things manually. There's a chance that your quotation marks are the "wrong" ones as there's a similar unicode character which looks similar but is NOT a quotation mark.

If you copy/pasted the code snippits off a website, that might be your problem.

As Jake has mentioned, the problem might be because of copy/paste code. Check the main.xml under res/layout. If there is no id field in that then you have a problem. A typical example would be as below

<com.androidplot.xy.XYPlot
android:id="@+id/mySimpleXYPlot"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_marginTop="10px"
android:layout_marginLeft="20px"
android:layout_marginRight="20px"
title="A Simple Example"
/>

Some times eclipse may confuse with other projects in the same directory.

Just change package name (don't forget to change in Android manifest file also), ensure the package name is not used already in the directory. It may work.

Just came across this myself.

Finally found my issue was with a .png file that I added that had a capital letter in it an caused exactly the same problem. Eclipse never flagged the file until I closed it and opened Eclipse back up.

What seems to be the problem, I just fixed mine in case anyone was wondering - Due to other errors i turned off build automatically, when i created a new project it said R.layout.main had an issue and needed to import R; So naturally as a novice, i did. Then i built manually and it had a problem with main. Try building your program as is, remove import R and it should be fine.

In main.xml (or wherever your item is defined) make sure that the ID for the R item is defined with @+id/... Here is an example with a button:

<Button android:text="B1" android:id="@+id/button_one"
        android:layout_gravity="center_horizontal|center"
        android:layout_height="fill_parent" android:layout_width="wrap_content" />

Each of these is important because:

• @ must precede the string
• + indicates it will create if not existing (whatever your item is)

I also had this error when I was working in a Java class once. My problem was simply that my xml file, with the references in it, was not saved. If you have both the xml file and java class open in tabs, check to make sure the xml file name in the tab doesn't have a * by it.

Hope this helps.

Just Clean your project so R will be generated automatically. This worked for me.

It gave me enough pain but I found the solution:

PROJECT ---> Clean ----> (Sele)

I had this problem but in my case it solved by restarting the eclipse.

For me the cause of the problem was that I had 2 images with the same name in my drawable-hdpi folder. Once I resolved that, then the R.java rebuilt itself and the problem was automatically solved.

select Project tab and click Build automatically so Build all option will be activated and then click on build all.and always start xml file name with lowercase.