java.lang.NullPointerException:尝试对空对象引用调用虚拟方法“int android.view.View.getImportantForAccessibility()”

nhhxz33t  于 2023-05-27  发布在  Android
关注(0)|答案(5)|浏览(212)

我正在尝试整合一个购物清单应用程序，基于输入字段ArrayList和ListView。该应用程序将基于Fragments。但是，我遇到了一个问题，我不知道如何解决它。
我在Google和StackOverflow上都找了一下，找到了一些信息。但是，我还没有让它工作。现在我希望我的代码能得到帮助。
我在Android开发方面相对缺乏经验。

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>

日志

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)
android

5条答案

按热度按时间
ercv8c1e

ercv8c1e1#

在public View getView方法中，将return null;更改为return convertView;。

赞(0）分享  回复(0）举报  2023-05-27
hgncfbus

hgncfbus2#

使用return convertView;

代码：

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;
}
赞(0）分享  回复(0）举报  2023-05-27
eaf3rand

eaf3rand3#

在你baseadapterclassconstructor中尝试初始化LayoutInflater，通常我更喜欢这种方式，

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

在类的顶部创建LayoutInflater变量，希望这对你有帮助

赞(0）分享  回复(0）举报  2023-05-27
mzsu5hc0

mzsu5hc04#

当我们在片段的任何活动中使用自定义适配器时，有时会发生这种情况。我们返回空对象，即空视图，因此Activity会混淆要加载哪个视图，这就是发生此异常的原因
shows the position where to change the view

赞(0）分享  回复(0）举报  2023-05-27
h7appiyu

h7appiyu5#

我的愚蠢错误是这样的：change！==

if(convertView != null) { // <---- HERE 
                LayoutInflater layoutInflater = LayoutInflater.from(z_selBoardElectricity.this);
                convertView = layoutInflater.inflate(R.layout.listview_board_alert, null);

                TextView textView = convertView.findViewById(R.id.board_name_tv);
                ImageView imageView = convertView.findViewById(R.id.board_imageview);

                textView.setText(text_list.get(position));
                imageView.setImageDrawable(imageAddressList.get(position));

                convertView.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        Intent intent = new Intent();
                        intent.putExtra("MESSAGE", text_list.get(pos));
                        setResult(98, intent);
                        finish();
                    }
                });
            }
return convertView;
赞(0）分享  回复(0）举报  2023-05-27
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