Nullpointer exception for SetBackgroundColour method in Android

Question

The xml code:

<RelativeLayout
    android:layout_width="193dp"
    android:layout_height="100dp"
    android:background="@color/RED"
    android:layout_alignParentBottom="true"
    android:id="@+id/butt1"></RelativeLayout>
<RelativeLayout
    android:layout_width="193dp"
    android:layout_height="100dp"
    android:background="@color/YELLOW"
    android:layout_alignParentBottom="true"
    android:layout_alignParentRight="true"
    android:id="@+id/butt2"></RelativeLayout>
<RelativeLayout
    android:layout_width="193dp"
    android:layout_height="100dp"
    android:background="@color/BLUE"
    android:layout_above="@+id/butt2"
    android:layout_alignParentRight="true"
    android:id="@+id/butt3"></RelativeLayout>
<RelativeLayout
    android:layout_width="193dp"
    android:layout_height="100dp"
    android:background="@color/GREEN"
    android:layout_above="@+id/butt1"
    android:id="@+id/butt4"></RelativeLayout>

The java code:

butt4 = (RelativeLayout)findViewById(R.id.butt4);
    butt3 = (RelativeLayout)findViewById(R.id.butt3);
    butt1 = (RelativeLayout)findViewById(R.id.butt1);
    butt2 = (RelativeLayout)findViewById(R.id.butt2);
  butt1.setBackgroundColor(Color.RED);
  butt2.setBackgroundColor(Color.BLUE);
  butt3.setBackgroundColor(Color.GREEN);
  butt4.setBackgroundColor(Color.YELLOW);

The Log:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 
'void android.view.View.setBackgroundColor(int)' on a null object reference
                                                                        at com.example.chirag.red.Hard.change(Hard.java:73)
                                                                        at com.example.chirag.red.Hard.onCreate(Hard.java:53)
                                                                        at android.app.Activity.performCreate(Activity.java:6672)
                                                                        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1140)
                                                                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2612)
                                                                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2724) 
                                                                        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1473) 
                                                                        at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                        at android.os.Looper.loop(Looper.java:154) 
                                                                        at android.app.ActivityThread.main(ActivityThread.java:6123) 
                                                                        at java.lang.reflect.Method.invoke(Native Method) 
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:757)

The app crashes every time this activity starts. The error is always at the line, "butt1.setBackgroundColor()" and it gives me a null pointer exception. I have given the layout an id, referenced it and also passed a color as the parameter in the method. I really don't see where i've gone wrong. Please help!

score 0 · Answer 1 · answered Aug 24 '17 at 20:28

0

This is the right way to do it:

 butt1.setBackgroundColor(getResources().getColor(R.color.red));

You have to define the color in your colors.xml

<color name="red">#ff0000</color>

answered Aug 24 '17 at 20:28

letsCode

2,774
1
13
37

Shows me the exact same error!! – Chirag Aug 24 '17 at 20:34
what else is in your xml? are those relative layouts surround by a parent? – letsCode Aug 24 '17 at 20:35
there is something else you aren't showing us. I ran a test app and that code I gave you works. so theres more to it than what you are showing us. – letsCode Aug 24 '17 at 20:38
My bad. I had set the layout to another similar layout. Thanks for your help! – Chirag Aug 24 '17 at 20:39
happy its fixed. good luck – letsCode Aug 24 '17 at 20:41

score 0 · Answer 2 · answered Aug 24 '17 at 20:36

0

You have a null... then could be some reasons

findViewById(xxxx) is returning null.

One - Check if is correcto your:

 android:id="@+id/xxx">

Two - The Java code correspond to the xml? could be make different references..

Put the complete code.

answered Aug 24 '17 at 20:36

josedlujan

5,357
2
27
49

My bad. I had set the layout to another similar layout. Thanks for your help! – Chirag Aug 24 '17 at 20:43
I know just select the answer that correct to help other people. – josedlujan Aug 24 '17 at 20:44

Nullpointer exception for SetBackgroundColour method in Android

2 Answers2