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Null pointer exception - Fragment Activity

 原文  2013-10-10 17:12:05  2   4    android/ layout/ android-activity/ fragment

Question

I'm fairly new to this and have managed to get the layout of my app and am using tabs and fragments.

Each layout is a different calculator and requires different calculations to run. Im struggling to figure out how to do this. Any help is much appreciated.

This first thing that i'm trying to get to work is the spinnersetup for the BMI fragment. Do I do this in the MainActivity or the Fragment? From what I have done so far I get a null pointer exception.

Here is my MainActivity code: 

public Fragment getItem(int position) {
            // getItem is called to instantiate the fragment for the given page.
            // Return a DummySectionFragment (defined as a static inner class
            // below) with the page number as its lone argument.
            switch (position) {
            case 0:
                Fragment fragment = new DummySectionFragment();
                Bundle args = new Bundle();
                args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
                fragment.setArguments(args);
                return fragment;

              case 1:
                Fragment fragment1 = new DummySectionFragment1();
                Bundle args1 = new Bundle();
                args1.putInt(DummySectionFragment1.ARG_SECTION_NUMBER, position + 2);
                fragment1.setArguments(args1);
                return fragment1;

              case 2:

                 Fragment fragment2 = new DummySectionFragment2();
                 Bundle args2 = new Bundle();
                 args2.putInt(DummySectionFragment2.ARG_SECTION_NUMBER, position + 3);
                 fragment2.setArguments(args2);
                 return fragment2;

              case 3:

                     Fragment fragment3 = new DummySectionFragment3();
                     Bundle args3 = new Bundle();
                     args3.putInt(DummySectionFragment3.ARG_SECTION_NUMBER, position + 4);
                     fragment3.setArguments(args3);
                     return fragment3;

            default:
                return null;
            }
        }

        @Override
        public int getCount() {
            // Show 4 total pages.
            return 4;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            Locale l = Locale.getDefault();
            switch (position) {
            case 0:
                return getString(R.string.title_section1).toUpperCase(l);
            case 1:
                return getString(R.string.title_section2).toUpperCase(l);
            case 2:
                return getString(R.string.title_section3).toUpperCase(l);
            case 3:
                return getString(R.string.title_section4).toUpperCase(l);
            }
            return null;
        }
    }

}

My Fragment code: 

package com.HealthKicks.bodystats.admob;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;

public class DummySectionFragment extends Fragment {

    EditText height_edit_text1, weight_edit_text1, height, weight;
    Spinner height_spinner, weight_spinner;
    Button calculatebmi;

    public static final String ARG_SECTION_NUMBER = "section_number";

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.bmi, container, false);

        setupSpinners();

        height_spinner =(Spinner) getView().findViewById(R.id.height_spinner);
        weight_spinner =(Spinner) getView().findViewById(R.id.weight_spinner);
        height_edit_text1 =(EditText) getView().findViewById(R.id.height_edit_text1);
        weight_edit_text1 =(EditText) getView().findViewById(R.id.weight_edit_text1);
        weight_spinner =(Spinner) getView().findViewById(R.id.weight_spinner);

        return rootView;
    }


    void setupSpinners() {

        height_spinner =(Spinner) getView().findViewById(R.id.height_spinner);
        weight_spinner =(Spinner) getView().findViewById(R.id.weight_spinner);
        height_edit_text1 =(EditText) getView().findViewById(R.id.height_edit_text1);
        weight_edit_text1 =(EditText) getView().findViewById(R.id.weight_edit_text1);

        // TODO Auto-generated method stub
            height_spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {

            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                if (position == 0){
                    height_edit_text1.setVisibility(View.GONE);
                } else {
                    height_edit_text1.setVisibility(View.VISIBLE);
                }
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });
                weight_spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
                    @Override
                    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                        if (position == 0){
                            weight_edit_text1.setVisibility(View.GONE);
                        } 
                        else if (position == 1){
                            weight_edit_text1.setVisibility(View.GONE);
                        }
                        else {
                            weight_edit_text1.setVisibility(View.VISIBLE);
                        }
                    }

                    @Override
                    public void onNothingSelected(AdapterView<?> parent) {

                    }
                });
    }   
}

LogCat: 

10-10 18:38:40.959: E/AndroidRuntime(1118): FATAL EXCEPTION: main
10-10 18:38:40.959: E/AndroidRuntime(1118): java.lang.NullPointerException
10-10 18:38:40.959: E/AndroidRuntime(1118):     at com.HealthKicks.bodystats.admob.DummySectionFragment.setupSpinners(DummySectionFragment.java:33)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at com.HealthKicks.bodystats.admob.DummySectionFragment.onCreateView(DummySectionFragment.java:26)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1478)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.View.measure(View.java:15848)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.View.measure(View.java:15848)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:302)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.View.measure(View.java:15848)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2189)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.View.measure(View.java:15848)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1905)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1104)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1284)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1004)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5481)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.Choreographer.doCallbacks(Choreographer.java:562)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.Choreographer.doFrame(Choreographer.java:532)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.os.Handler.handleCallback(Handler.java:730)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.os.Handler.dispatchMessage(Handler.java:92)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.os.Looper.loop(Looper.java:137)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at android.app.ActivityThread.main(ActivityThread.java:5103)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at java.lang.reflect.Method.invokeNative(Native Method)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at java.lang.reflect.Method.invoke(Method.java:525)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-10 18:38:40.959: E/AndroidRuntime(1118):     at dalvik.system.NativeStart.main(Native Method)

4 answers

solution1
 2 ACCPTED  2013-10-11 15:29:10

Change onCreateView from this: 

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.bmi, container, false);
    setupSpinners();
    height_spinner = (Spinner) getView().findViewById(R.id.height_spinner);
    weight_spinner = (Spinner) getView().findViewById(R.id.weight_spinner);
    height_edit_text1 = (EditText) getView().findViewById(R.id.height_edit_text1);
    weight_edit_text1 = (EditText) getView().findViewById(R.id.weight_edit_text1);
    weight_spinner = (Spinner) getView().findViewById(R.id.weight_spinner);
    return rootView;
}

to this: 

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.bmi, container, false);
    height_spinner = (Spinner) rootView.findViewById(R.id.height_spinner);
    weight_spinner = (Spinner) rootView.findViewById(R.id.weight_spinner);
    height_edit_text1 = (EditText) rootView.findViewById(R.id.height_edit_text1);
    weight_edit_text1 = (EditText) rootView.findViewById(R.id.weight_edit_text1);
    weight_spinner = (Spinner) rootView.findViewById(R.id.weight_spinner);
    return rootView;
}

Call setupSpinners from onViewCreated : 

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    setupSpinners();
}

and it would be more efficient if you pass the view as parameter so don't call everytime getView() :

solution2
 0  2013-10-10 18:59:23

You are running your initialization of all your members twice.

In the body of onCreateView() you call setupSpinners(); which initializes your members, and then you re-initialize them. Initialize them in one place only.

solution3
 0  2013-10-10 22:59:23

None of your views are initialized in your DummySectionFragment. You have to tell what is each Spinner, something like: 

height_spinner = (Spinner) getView().findViewById(R.id.theIdInTheLayoutFile);

solution4
 0  2014-03-21 19:38:50

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.bmi, container, false);
    height_spinner = (Spinner) rootView.findViewById(R.id.height_spinner);
    weight_spinner = (Spinner) rootView.findViewById(R.id.weight_spinner);
    height_edit_text1 = (EditText) rootView.findViewById(R.id.height_edit_text1);
    weight_edit_text1 = (EditText) rootView.findViewById(R.id.weight_edit_text1);
    weight_spinner = (Spinner) rootView.findViewById(R.id.weight_spinner);

    setUpSpinners(rootView);  
    return rootView;
}

protected void setUpSpinners(pass rootview here...)
{
      ...use spinners as 
      Spinner weight_spinner = (Spinner) rootView.findViewById(R.id.weight_spinner);
}

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