NullPointerException using Array of Custom Views

Question

I decided to optimize my code using a simple loop instead of hardcode, because previously I implemented each PickView separately and it worked fine.

Here is a problematic place:

pick = new PickView[9];
int id;
for(int i = 0; i < pick.length; i++) {
    id = getResources().getIdentifier("pick_" + i, "id", getPackageName());
    pick[i] = (PickView)findViewById(id);
    pick[i].setOnTouchListener(this); //this is MainActivity, line:54
}

...in which unexpectedly I recieved a NullPointerException:

ERROR/AndroidRuntime(8450): FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.***}: java.lang.NullPointerException
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
    at android.app.ActivityThread.access$2300(ActivityThread.java:125)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:123)
    at android.app.ActivityThread.main(ActivityThread.java:4627)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:521)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
    at dalvik.system.NativeStart.main(Native Method)
    Caused by: java.lang.NullPointerException
    at com.***.onCreate(MainActivity.java:54)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
    ... 11 more

I enclose a PickView class:

public class PickView extends RelativeLayout {

    private TextView textView;
    private ImageView imageView;
    private String text;

    public PickView(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.PickView);
        text = a.getString(R.styleable.PickView_text);

        LayoutInflater layoutInflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View view = layoutInflater.inflate(R.layout.pick_view, this);
        textView = (TextView)findViewById(R.id.pick_text);
        imageView = (ImageView)findViewById(R.id.pick_bg);
    }

    public void setText(String text) {
        textView.setText(text);
    }

    public void activate(boolean isActive) {
        if (isActive)
            imageView.setImageResource(R.drawable.pick_active);
        else
            imageView.setImageResource(R.drawable.pick);
    }
}

I will be grateful for any help!

(PickView)findViewById(id); return null ... why ? i'dont know ... show us more code ... maybe you call it before setContentView ... — Selvin
– Selvin, Commented Sep 6, 2012 at 13:22
You havn't initialized your array pick, try this first as in java, arrays must be initialized after declaration. — engineer
– engineer, Commented Sep 6, 2012 at 13:22
@engineer iteresting ... so what this line do: pick = new PickView[9]; ? — Selvin
– Selvin, Commented Sep 6, 2012 at 13:23

Raanan · Accepted Answer · 2012-09-06 13:25:38Z

1

Just a small question do you have a pick_0 resource?

And anyway you should check that you are actually getting an id and that the PickView returned isn't null?

answered Sep 6, 2012 at 13:25

Raanan

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1 Comment

pawegio Over a year ago

You made my day! I had ids from "pick_1" to "pick_9". What a simple mistake... Thanks a lot! Stackoverflow rocks ;)

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

Java doc of getIdentifier suggests that it return 0 if not found that is the cause of your problem. So findViewById returns null if not found.

public int getIdentifier (String name, String defType, String defPackage)

Return a resource identifier for the given resource name. A fully qualified resource name is of the form "package:type/entry". The first two components (package and type) are optional if defType and defPackage, respectively, are specified here.

Note: use of this function is discouraged. It is much more efficient to retrieve resources by identifier than by name.

int The associated resource identifier. Returns 0 if no such resource was found. (0 is not a valid resource ID.)

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Sep 6, 2012 at 13:25

Amit Deshpande

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1 Comment

Amit Deshpande Over a year ago

Yes findViewById returns null if not found.

Kai Huppmann · Accepted Answer · 2012-09-06 13:32:57Z

1

Maybe you can find it that way:

for (int i = 0; i < pick.length; i++)
{
  resources = getResources();
  if(resources == null)
  {
    System.out.println("oops.. no resources");
    throw new RuntimeException("oops... no resources");
  }
  id = resources.getIdentifier("pick_" + i, "id", getPackageName());
  pickView = (PickView) findViewById(id);
  if(resources == null)
  {
    System.out.println("oops.. noo pickView");
    throw new RuntimeException("oops... no pickView");
  }
  pick[i] = pickView;
  pick[i].setOnTouchListener(this); //this is MainActivity, line:54
}

answered Sep 6, 2012 at 13:32

Kai Huppmann

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1 Comment

pawegio Over a year ago

It would be much, safer. ;) Next time I will write sth like this. Problem is solved by Raanan.

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