java.lang.NullPointerException: tentative d'appel de la méthode virtuelle 'int android.view.View.getImportantForAccessibility ()' sur une référence d'objet null

original title: "java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getImportantForAccessibility()' on a null object reference"


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I'm trying to put together a shopping list app, based on input fields, ArrayList, and ListView. The app will be based on Fragments. However, I have encountered a problem and I do not know how to solve it.

I looked around on both Google and StackOverflow and I have found some information. However, I have not got it to work. Now I hope that I can get help with my code.

I'm relatively inexperienced in Android development .

Thanks in advance

Main.java

import java.util.ArrayList;

import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.Menu;
import android.view.MenuItem;

public class Main extends FragmentActivity {

    ArrayList<Detail> items = new ArrayList<Detail>();
    FragmentManager FM;
    FragmentTransaction FT;
    Input input = new Input();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        replaceFragment(R.id.container, input);
    }


    public void replaceFragment(int container, Fragment fragment){
        FM = getFragmentManager();
        FT = FM.beginTransaction();

        FT.replace(container, fragment);
        FT.commit();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

ListAdapter.java

public class ListAdapter extends BaseAdapter {

    Context context;
    ArrayList<Detail> items;

    public ListAdapter(Context context, ArrayList<Detail> items) {
        this.context = context;
        this.items = items;
    }

    @Override
    public int getCount() {
        return items.size();
    }

    @Override
    public Object getItem(int position) {
        return items.get(position);
    }

    @Override
    public long getItemId(int position) {
        return items.indexOf(getItem(position));
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        if(convertView == null){
            LayoutInflater lInflater = (LayoutInflater)context.getSystemService(
                    Activity.LAYOUT_INFLATER_SERVICE);

            convertView = lInflater.inflate(R.layout.list_row, null);       
        }

        TextView title = (TextView)convertView.findViewById(R.id.itemTitle);
        CheckBox done = (CheckBox)convertView.findViewById(R.id.itemDone);


        Detail detail_position = items.get(position);

        title.setText(detail_position.getTitle());
        done.setChecked(detail_position.isDone());

        return null;
    }
}

List.java

import java.util.ArrayList;

import android.app.ListFragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;

public class List extends ListFragment implements OnItemClickListener{

    ArrayList<Detail> items;
    ListAdapter adapter;
    private onClickListener OCL;

    interface onClickListener{
        public void onItemClick(int id);
    }

    public List(ArrayList<Detail> items) {
        this.items = items;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        View root = inflater.inflate(R.layout.list_layout, container, false);
        return root;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        if(items != null){
            adapter = new ListAdapter(getActivity(), items);
            setListAdapter(adapter);
            getListView().setOnItemClickListener(this);
        }

    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
            long id) {

        if(OCL != null){
            OCL.onItemClick(position);
        }       
    }
}

list_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/LinearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    <ListView
        android:id="@+id/android:list"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
    </ListView>
</LinearLayout>

list_row

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:padding="10dp" >
    <TextView
        android:id="@+id/itemTitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="0.96"
        android:text="Medium Text"
        android:textAppearance="?android:attr/textAppearanceMedium" />
    <CheckBox
        android:id="@+id/itemDone"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Done" />
</LinearLayout>

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.com.hermods.lab2_2.Main" >
</RelativeLayout>

Log

02-19 09:10:47.421: E/AndroidRuntime(12745): Process: com.example.com.hermods.lab2_2, PID: 12745
02-19 09:10:47.421: E/AndroidRuntime(12745): java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getImportantForAccessibility()' on a null object reference
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.AbsListView.obtainView(AbsListView.java:2360)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.ListView.makeAndAddView(ListView.java:1864)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.ListView.fillDown(ListView.java:698)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.ListView.fillFromTop(ListView.java:759)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.ListView.layoutChildren(ListView.java:1673)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.AbsListView.onLayout(AbsListView.java:2148)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1076)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.widget.FrameLayout.onLayout(FrameLayout.java:508)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.View.layout(View.java:15596)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewGroup.layout(ViewGroup.java:4966)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2072)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1829)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.Choreographer.doCallbacks(Choreographer.java:580)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.Choreographer.doFrame(Choreographer.java:550)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.os.Handler.handleCallback(Handler.java:739)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.os.Handler.dispatchMessage(Handler.java:95)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.os.Looper.loop(Looper.java:135)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at android.app.ActivityThread.main(ActivityThread.java:5221)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at java.lang.reflect.Method.invoke(Native Method)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at java.lang.reflect.Method.invoke(Method.java:372)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
02-19 09:10:47.421: E/AndroidRuntime(12745):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)


J'essaie de créer une application de liste de courses, basée sur les champs de saisie, ArrayList et ListView. L'application sera basée sur des fragments. Cependant, j'ai rencontré un problème et je ne sais pas comment ...

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Toutes les réponses
  • Translate

    In your public View getView method change return null; to return convertView;.


  • Translate

    #use return convertView;

    Code:

    public View getView(final int position, View convertView, ViewGroup parent) {
    
        //convertView = null;
    
        if (convertView == null) {
    
            LayoutInflater mInflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
            convertView = mInflater.inflate(R.layout.list_item, null);     
    
            TextView tv = (TextView) convertView.findViewById(R.id.name);
            Button rm_btn = (Button) convertView.findViewById(R.id.rm_btn);
    
            Model m = modelList.get(position);
            tv.setText(m.getName());
    
            // click listener for remove button  คลิกลบปุ่ม
            rm_btn.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    modelList.remove(position);
                    notifyDataSetChanged();
                }
            });
        }
    
        ///#use    return convertView;
        return convertView;
    }
    

  • Translate

    in your baseadapter class constructor try to initialize LayoutInflater, normally i preferred this way,

    public ClassBaseAdapter(Context context,ArrayList<Integer> listLoanAmount) {
        this.context = context;
        this.listLoanAmount = listLoanAmount;
        this.layoutInflater = LayoutInflater.from(context);
    }
    

    at the top of the class create LayoutInflater variable, hope this will help you


  • Translate

    it sometimes occurs when we use a custom adapter in any activity of fragment . and we return null object i.e null view so the activity gets confused which view to load , so that is why this exception occurs

    shows the position where to change the view