Question

尝试在片段（SessionsFragment.java）中的ImageButton上设置onClickListener，并且我不断获得空指针异常。尝试了所有不同的解决方案，仍然得到相同的错误。该按钮位于ExpandableListView中的项目中，因此我添加了list_item.xml。看到一些评论说它是空的，因为它不属于主要活动或类似的东西。无论如何，我怎么能克服这个？

SessionsFragment.java

public class SessionsFragment extends Fragment {

ExpandableListAdapter expandableListAdapter;
ExpandableListView expandableListView;
List<String> listDataHeader;
HashMap<String, List<String>> listDataChild;
ImageButton addButton;

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

    // Get the ListView
    expandableListView = view.findViewById(R.id.sessionsExpandableListView);

    // Prepare the list data
    prepareListData();

    expandableListAdapter = new ExpandableListAdapter(getContext(), listDataHeader, listDataChild);

    // Set the list adapter and expand lists by default
    expandableListView.setAdapter(expandableListAdapter);
    expandableListView.expandGroup(0);

    // Get button values
    addButton = view.findViewById(R.id.addButton);
    addButton.setOnClickListener(new ImageButton.OnClickListener() {
        @Override
        public void onClick(View view) {
            Toast.makeText(getActivity(), "Session added", Toast.LENGTH_SHORT).show();
        }
    });

    return view;
}

list_item.xml

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="55dp">

<TextView
    android:id="@+id/listItem"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="16sp"
    android:paddingTop="5dp"
    android:paddingBottom="5dp" />
    <!--android:paddingLeft="?android:attr/expandableListPreferredChildPaddingLeft"/>-->

<ImageButton
    android:id="@+id/addButton"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:src="@drawable/ic_add_black_24dp"
    android:layout_alignParentRight="true" />

logcat的

04-25 15：12：04.053 11894-11901 /？ E / zygote64：发送回复失败调试器：管道坏了 04-25 15：12：04.578 11894-11894 /？ E / AndroidRuntime：致命异常：主要过程：com.example.android.engineeringweek，PID：11894 java.lang.RuntimeException：无法启动活动 ComponentInfo {com.example.android.engineeringweek / com.example.android.engineeringweek.SessionsActivity}： java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.widget.ImageButton.setOnClickListener（android.view.View $ OnClickListener）＆＃39; 在null对象引用上在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2946）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3046）在android.app.ActivityThread.-wrap11（未知来源：0）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1688）在android.os.Handler.dispatchMessage（Handler.java:105）在android.os.Looper.loop（Looper.java:164）在android.app.ActivityThread.main（ActivityThread.java:6809） at java.lang.reflect.Method.invoke（Native Method）在com.android.internal.os.Zygote $ MethodAndArgsCaller.run（Zygote.java:240）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:767）引起：java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.widget.ImageButton.setOnClickListener（android.view.View $ OnClickListener）＆＃39; 在null对象引用上在com.example.android.engineeringweek.SessionsFragment.onCreateView（SessionsFragment.java:47）在android.support.v4.app.Fragment.performCreateView（Fragment.java:2354）在android.support.v4.app.FragmentManagerImpl.moveToState（FragmentManager.java:1419）在android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState（FragmentManager.java:1740）在android.support.v4.app.FragmentManagerImpl.moveToState（FragmentManager.java:1809）在android.support.v4.app.BackStackRecord.executeOps（BackStackRecord.java:799）在android.support.v4.app.FragmentManagerImpl.executeOps（FragmentManager.java:2580）在android.support.v4.app.FragmentManagerImpl.executeOpsTogether（FragmentManager.java:2367）在android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute（FragmentManager.java:2322）在android.support.v4.app.FragmentManagerImpl.execPendingActions（FragmentManager.java:2229）在android.support.v4.app.FragmentManagerImpl.dispatchStateChange（FragmentManager.java:3221）在android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated（FragmentManager.java:3171）在android.support.v4.app.FragmentController.dispatchActivityCreated（FragmentController.java:192）在android.support.v4.app.FragmentActivity.onStart（FragmentActivity.java:560）在android.support.v7.app.AppCompatActivity.onStart（AppCompatActivity.java:177）在android.app.Instrumentation.callActivityOnStart（Instrumentation.java:1412）在android.app.Activity.performStart（Activity.java:7015）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2909）

修改

ExpandableListAdapter.java

public class ExpandableListAdapter extends BaseExpandableListAdapter {
    private Context _context;
    private List<String> _listDataHeader;
    private HashMap<String, List<String>> _listDataChild;

    public ExpandableListAdapter(Context context, List<String> listDataHeader, HashMap<String, List<String>> listDataChild) {
        this._context = context;
        this._listDataHeader = listDataHeader;
        this._listDataChild = listDataChild;
    }

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

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

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

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        String headerTitle = (String) getGroup(groupPosition);
        if(convertView == null) {
            LayoutInflater layoutInflater = (LayoutInflater) this._context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = layoutInflater.inflate(R.layout.list_group, null);
        }

        TextView listHeader = convertView.findViewById(R.id.listHeader);
        listHeader.setTypeface(null, Typeface.BOLD);
        listHeader.setText(headerTitle);

        return convertView;
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        return this._listDataChild.get(this._listDataHeader.get(groupPosition)).get(childPosition);
    }

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

    @Override
    public View getChildView(int groupPosition, final int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        final String childText = (String) getChild(groupPosition, childPosition);

        if(convertView == null) {
            LayoutInflater layoutInflater = (LayoutInflater) this._context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = layoutInflater.inflate(R.layout.list_item, null);
        }

        TextView textListChild = convertView.findViewById(R.id.listItem);

        textListChild.setText(childText);

        return convertView;
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return this._listDataChild.get(this._listDataHeader.get(groupPosition)).size();
    }

    @Override
    public boolean isChildSelectable(int i, int i1) {
        return true;
    }

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

Answer 1

看来你的findViewById找不到id addButton。查看完代码后，我发现您正在查看R.layout.fragment_sessions作为您的视图，但会搜索您的listitem中包含的ID。

如果要将clicklistener添加到列表项，则需要在创建/绑定视图符时在适配器类中执行此操作。

尝试在Fragment

1 个答案: