BaseExpandableListAdapter RuntimeError NullPointerException

Question

我正在尝试在 ExpandableListView 中查看数据库中的数据（我首先尝试使用硬编码字符串）。

我使用了以下示例：CodeWiki ExpandableListView

但是当我点击一个组来获取 childView 时，我得到了一个运行时错误。

Categories1.java

public class CategoriesActivity1 extends Activity

{

ExpandableListView eListView;
ExpandableListAdapter eListAdapter;

ArrayList<String> groups;
ArrayList<ArrayList<ArrayList<String>>> children;

 @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.categories);

        eListView = (ExpandableListView)findViewById(R.id.expandableListView1);

        loadData();

        MyExpandableListAdapter adapter = new MyExpandableListAdapter(this, groups, children);

        eListView.setAdapter(adapter);


 }



 private void loadData(){

        groups= new ArrayList<String>();
        children= new ArrayList<ArrayList<ArrayList<String>>>();

        groups.add("Group 1");
        groups.add("Group 2");
        groups.add("Group 3");

        children.add(new ArrayList<ArrayList<String>>());
        children.get(0).add(new ArrayList<String>());
        children.get(0).get(0).add("Child 1 group 1");
        children.get(0).add(new ArrayList<String>());
        children.get(0).get(1).add("Child 2 group 1");
        children.get(0).add(new ArrayList<String>());
        children.get(0).get(2).add("Child 3 group 1");

        children.add(new ArrayList<ArrayList<String>>());
        children.get(1).add(new ArrayList<String>());
        children.get(1).get(0).add("Child 1 group 2");
        children.get(1).add(new ArrayList<String>());
        children.get(1).get(1).add("Child 2 group 2");
        children.get(1).add(new ArrayList<String>());
        children.get(1).get(2).add("Child 3 group 2");

        children.add(new ArrayList<ArrayList<String>>());
        children.get(2).add(new ArrayList<String>());
        children.get(2).get(0).add("Child 1 group 3");
        children.get(2).add(new ArrayList<String>());
        children.get(2).get(1).add("Child 2 group 3");
        children.get(2).add(new ArrayList<String>());
        children.get(2).get(2).add("Child 3 group 3");
    }

}

MyExpandableListAdapter.java

public class MyExpandableListAdapter extends BaseExpandableListAdapter

{

private ArrayList<String> groups;
    private ArrayList<ArrayList<ArrayList<String>>> children;
    private Context context;

public MyExpandableListAdapter(Context context, ArrayList<String> groups, ArrayList<ArrayList<ArrayList<String>>> children)
{
    this.context = context;
    this.groups = groups;
    this.children = children;
}

@Override
public boolean areAllItemsEnabled()
{
    return true;
}

@Override
public ArrayList<String> getChild(int groupPosition, int childPosition)
{
    return children.get(groupPosition).get(childPosition);
}

@Override
public long getChildId(int groupPosition, int childPosition)
{
    return childPosition;
}

@Override
public View getChildView(int groupPosition, int childPosition,
        boolean isLastChild, View convertView, ViewGroup parent)
{
    String child = (String) ((ArrayList<String>)getChild(groupPosition, childPosition)).get(0);

    if(convertView == null)
    {
        LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = layoutInflater.inflate(R.layout.categories_group, null);
    }

    TextView childTxt = (TextView)convertView.findViewById(R.id.TextViewChild01);

    childTxt.setText(child);

    return convertView;
}

@Override
public int getChildrenCount(int groupPosition)
{
    return children.get(groupPosition).size();
}

@Override
public Object getGroup(int groupPosition)
{
    return groups.get(groupPosition);
}

@Override
public int getGroupCount()
{
    return groups.size();
}

@Override
public long getGroupId(int groupPosition)
{
    return groupPosition;
}

@Override
public View getGroupView(int groupPosition, boolean isExpanded,
        View convertView, ViewGroup parent)
{
    String group = (String) getGroup(groupPosition);

    if(convertView == null)
    {
        LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = layoutInflater.inflate(R.layout.categories_group, null);
    }

    TextView groupTxt = (TextView) convertView.findViewById(R.id.TextViewGroup);

    groupTxt.setText(group);


    return convertView;
}

@Override
public boolean hasStableIds()
{
    return true;
}

@Override
public boolean isChildSelectable(int groupPosition, int childPosition)
{
    return true;
}

}

categories_group.xml

     <?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/categoriesLLayout2"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <TextView
        android:id="@+id/TextViewGroup" 
        android:layout_width="wrap_content"
        android:layout_height="50dp"
        android:layout_marginLeft="50dp"
        android:gravity="center_vertical"
    >
    </TextView>
    <TextView
        android:id="@+id/TextViewChild01" 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="30dp"
    >
    </TextView>
</LinearLayout>

Logcat：

03-17 15:16:13.468：E/AndroidRuntime(370)：致命异常：主要 03-17 15:16:13.468: E/AndroidRuntime(370): java.lang.NullPointerException 03-17 15:16:13.468: E/AndroidRuntime(370): 在 nl.test.listing.activity.MyExpandableListAdapter.getChildView(MyExpandableListAdapter.java:64) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.ExpandableListConnector.getView(ExpandableListConnector.java:450) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.AbsListView.obtainView(AbsListView.java:1430) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.ListView.measureHeightOfChildren(ListView.java:1216) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.ListView.onMeasure(ListView.java:1127) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.LinearLayout.measureVertical(LinearLayout.java:386) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.LinearLayout.onMeasure(LinearLayout.java:309) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.FrameLayout.onMeasure(FrameLayout.java:250) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.LinearLayout.measureVertical(LinearLayout.java:531) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.LinearLayout.onMeasure(LinearLayout.java:309) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.widget.FrameLayout.onMeasure(FrameLayout.java:250) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.ViewRoot.performTraversals(ViewRoot.java:839) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.view.ViewRoot.handleMessage(ViewRoot.java:1859) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.os.Handler.dispatchMessage(Handler.java:99) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.os.Looper.loop(Looper.java:123) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 android.app.ActivityThread.main(ActivityThread.java:3683) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 java.lang.reflect.Method.invokeNative(Native Method) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 java.lang.reflect.Method.invoke(Method.java:507) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 03-17 15:16:13.468: E/AndroidRuntime(370): 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 03-17 15:16:13.468: E/AndroidRuntime(370): at dalvik.system.NativeStart.main(Native Method)

我不知道为什么会出现这个错误，查看示例我只将 xml 值从 px 更改为 dp。

Answer 1

我认为问题出在第 64 行的“MyExpandableListAdapter”类。这里似乎有一些变量在那一刻变为空。你能在这个类的第 64 行粘贴代码吗？以便我可以为您提供更多帮助。