NullPointerException with ImageButtons Array

Question

I declared an ImageButton array manually and then add some ImageButtons manually to it, and after assigning these ImageButtons to the XML layout, I tried to iterate through that array using a for loop, but I'm getting a NullPointerException when iterating through that array(the Exception comes with the first Iterate it's not even manage the iteration once), that's my code:

public ImageButton Antenna, AV, Components, VGA, HDMI, Switch;
public ImageButton[] upControllingButtons = {Antenna, AV, Components, VGA, HDMI, Switch};
        Antenna = (ImageButton) findViewById(R.id.antenna);
            // then the other six ImageButtons

        // setting the onClick for the Up_Controlling butoons
        for(int k=0; k < upControllingButtons.length ; k++ ){
            upControllingButtons[k].setTag("tag"); // i got the Exception here
        }

and the ImageButton in the XML:

                            <ImageButton
                                android:id="@+id/antenna"
                                android:layout_width="wrap_content"
                                android:layout_height="wrap_content"
                                android:layout_gravity="center"
                                android:layout_marginLeft="7dp"
                                android:layout_marginRight="7dp"
                                android:adjustViewBounds="true"
                                android:background="@drawable/remote_living_buttons"
                                android:clickable="true"
                                android:padding="8dp"
                                android:scaleType="centerInside"
                                android:src="@drawable/remote_living_antena"
                                android:tag="released" />
                                <!.. then the other six ..!>

and that is the LogCat result:

01-23 11:43:11.068: ERROR/AndroidRuntime(589): FATAL EXCEPTION: main
01-23 11:43:11.068: ERROR/AndroidRuntime(589): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.solaceap/com.example.solaceap.RemoteTV}: java.lang.NullPointerException
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.app.ActivityThread.access$600(ActivityThread.java:122)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.os.Looper.loop(Looper.java:137)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.app.ActivityThread.main(ActivityThread.java:4340)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at java.lang.reflect.Method.invokeNative(Native Method)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at java.lang.reflect.Method.invoke(Method.java:511)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at dalvik.system.NativeStart.main(Native Method)
01-23 11:43:11.068: ERROR/AndroidRuntime(589): Caused by: java.lang.NullPointerException
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at com.example.solaceap.RemoteTV.get_available_devices(RemoteTV.java:221)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at com.example.solaceap.RemoteTV.onCreate(RemoteTV.java:81)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.app.Activity.performCreate(Activity.java:4465)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-23 11:43:11.068: ERROR/AndroidRuntime(589):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)

@Raghunandan If you read the code properly (and his comment) he uses findViewById on all 6, so does initialise them all. Its not clear though due to him having hid the code. — IAmGroot
– IAmGroot, Commented Jan 23, 2014 at 10:06

NarendraSoni · Accepted Answer · 2014-01-23 10:10:44Z

5

Try inflating first then add to the array like:

 Antenna = (ImageButton) findViewById(R.id.antenna);
 ...
 ...
 public ImageButton[] upControllingButtons = {Antenna, AV, Components, VGA, HDMI, Switch};

answered Jan 23, 2014 at 10:10

NarendraSoni

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Sivakumar Purushothaman · Accepted Answer · 2014-01-23 10:16:27Z

0

public ImageButton[] upControllingButtons = new ImageButton[7];
Antenna = (ImageButton) findViewById(R.id.antenna);
//Then Do your work

hope this will help

answered Jan 23, 2014 at 10:16

Sivakumar Purushothaman

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Muhammad Aamir Ali · Accepted Answer · 2014-01-23 10:21:51Z

Your approch is wrong do not use separate line for each ImageButton to initialize you can use loop instead.

try this.

You have to give the ids of your ImageButton by numbers. like

<ImageButton
     android:id="@+id/button1"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content" />

<ImageButton
     android:id="@+id/button2"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content" />


<ImageButton
     android:id="@+id/button3"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content" />

ArrayList<ImageButton> upControllingButtons = new ArrayList<ImageButton>();
for(int i=0; i<3; i++)
{
    upControllingButtons .add(getImageButton(i));
}


private ImageButton getImageButton(int i)
{
    int id=0;

     try {
         id = R.id.class.getField("button" + i).getInt(0);
        }
     catch (IllegalArgumentException e){
         e.printStackTrace();
     } catch (SecurityException e) {
         e.printStackTrace();
     } catch(IllegalAccessException e) {
         e.printStackTrace();
     } catch (NoSuchFieldException e) {
         e.printStackTrace();
     }
     ImageButton imageButton = (ImageButton)findViewById(id);
             return imageButton
}

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