NullPointerException: 尝试在 null 对象引用上调用虚方法‘ int android.view. View.getImport antForAccability ()’

我试图把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。然而，我遇到了一个问题，我不知道如何解决它。

我查看了 Google 和 StackOverflow，发现了一些信息。然而，我还没有得到它的工作。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。

缅因州，爪哇

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);
}
}

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;
}
}

列表.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 _ lay.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>

木头

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)
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小开
最佳答案

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

小开

# 使用 return convertView;

密码:

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;
}
小开

在你的 基本适配器类 构造函数尝试初始化 布局，通常我喜欢这种方式,

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 布局变量，希望这将对您有所帮助

小开

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 null 对象，即 null 视图，这样活动就会混淆要加载哪个视图，这就是为什么会发生这个异常

显示更改视图的位置

小开

我犯了一个愚蠢的错误: 改变

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;

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