Question

I have

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/mainRelativeLayout">

and I’m trying to setup the background using java code (I don’t want to do it in xml) using this code in onCreate method:

View view = (View)findViewById(R.id.mainRelativeLayout);
        view.setBackgroundColor(0xFF000000);

or this code:

View view = (View)findViewById(R.id.mainRelativeLayout);
        view.setBackgroundColor(android.R.color.white);

However, it fails at first line when it tries to find the id. Where’s the problem? Thanks

start of my onCreate() code:

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getPrefs();
        if (themePreference) {
            setTheme(android.R.style.Theme_Light_NoTitleBar);
        }else{
            setTheme(android.R.style.Theme_Black_NoTitleBar);
        }
        setContentView(R.layout.main);
        /*View view = (View)findViewById(R.id.mainRelativeLayout);
        view.setBackgroundColor(0xFF000000);*/

        SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);

        this.submitBtn = (Button) this.findViewById(R.id.submitBtn);
        this.cleanBtn = (Button) this.findViewById(R.id.clear_txt_Input);
        this.inputQ = (EditText) this.findViewById(R.id.inputQ);
        ...

stack trace:

myApp [Android Application] 
    DalvikVM[localhost:8610]    
        Thread [<1> main] (Suspended (exception RuntimeException))  
            ActivityThread.performLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 1768    
            ActivityThread.handleLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 1784 
            ActivityThread.access$1500(ActivityThread, ActivityThread$ActivityClientRecord, Intent) line: 123   
            ActivityThread$H.handleMessage(Message) line: 939   
            ActivityThread$H(Handler).dispatchMessage(Message) line: 99 
            Looper.loop() line: 130 
            ActivityThread.main(String[]) line: 3835    
            Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]  
            Method.invoke(Object, Object...) line: 507  
            ZygoteInit$MethodAndArgsCaller.run() line: 847  
            ZygoteInit.main(String[]) line: 605 
            NativeStart.main(String[]) line: not available [native method]  
        Thread [<8> Binder Thread #2] (Running) 
        Thread [<7> Binder Thread #1] (Running) 

Answer 1

Were you able to run your app successfully without changing the background color? Because I was able to run a simplified version of your code without any errors. I think your error might be elsewhere.

Have you tried using Project > Clean to clean and rebuild your project?

Here is the test code I used.

The Activity:

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    View view = findViewById(R.id.mainLayout);
    view.setBackgroundColor(0xFFEE3333);
}

And the XML:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/mainLayout">

    <Button
    android:id="@+id/button"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="Stack Overflow"/>

</RelativeLayout>