Question

我有一个ListFragment，我想使用自定义布局。布局非常好，所有资源都在他们的位置。但我仍然得到Null Pointer Exception。

列表片段代码：

public class InboxFragment extends ListFragment {

protected List<ParseObject> mMessages;

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

    return rootView;
}

@Override
public void onResume() {
    super.onResume();

    getActivity().setProgressBarIndeterminateVisibility(true);

    ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(ParseConstants.CLASS_MESSAGES);
    query.whereEqualTo(ParseConstants.KEY_RECIPIENT_IDS, ParseUser.getCurrentUser().getObjectId());
    query.addDescendingOrder(ParseConstants.KEY_CREATED_AT);
    query.findInBackground(new FindCallback<ParseObject>() {
        @Override
        public void done(List<ParseObject> messages, ParseException e) {
            getActivity().setProgressBarIndeterminateVisibility(false);

            if (e == null) {
                // We found messages!
                mMessages = messages;

                String[] usernames = new String[mMessages.size()];
                int i = 0;
                for(ParseObject message : mMessages) {
                    usernames[i] = message.getString(ParseConstants.KEY_SENDER_NAME);
                    i++;
                }
                MessageAdapter adapter = new MessageAdapter(
                        getListView().getContext(),
                        mMessages);
                setListAdapter(adapter);
            }
        }
    });
}

@Override
public void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id);

    ParseObject message = mMessages.get(position);
    String messageType = message.getString(ParseConstants.KEY_FILE_TYPE);
    ParseFile file = message.getParseFile(ParseConstants.KEY_FILE);
    Uri fileUri = Uri.parse(file.getUrl());

    if (messageType.equals(ParseConstants.TYPE_IMAGE)) {
        // view the image
        Intent intent = new Intent(getActivity(), ViewImageActivity.class);
        intent.setData(fileUri);
        startActivity(intent);
    }
    else {
        // view the video
        Intent intent = new Intent(Intent.ACTION_VIEW, fileUri);
        intent.setDataAndType(fileUri, "video/*");
        startActivity(intent);
    }
}

}

我与此片段一起使用的适配器：

public class MessageAdapter extends ArrayAdapter<ParseObject> {

protected Context mContext;
protected List<ParseObject> mMessages;

public MessageAdapter(Context context, List<ParseObject> messages) {
    super(context, R.layout.message_item, messages);
    mContext = context;
    mMessages = messages;
}

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

    if (convertView == null) {
        convertView = LayoutInflater.from(mContext).inflate(R.layout.message_item, null);
        holder = new ViewHolder();
        holder.iconImageView = (ImageView)convertView.findViewById(R.id.messageIcon);
        holder.nameLabel = (TextView)convertView.findViewById(R.id.senderLabel);
    }
    else {
        holder = (ViewHolder)convertView.getTag();
    }

    ParseObject message = mMessages.get(position);
    if (message.getString(ParseConstants.KEY_FILE_TYPE).equals(ParseConstants.TYPE_IMAGE)) {
        holder.iconImageView.setImageResource(R.drawable.ic_action_picture);
    }
    else {
        holder.iconImageView.setImageResource(R.drawable.ic_action_play_over_video);
    }
    holder.nameLabel.setText(message.getString(ParseConstants.KEY_SENDER_NAME));

    return convertView;
}

private static class ViewHolder {
    ImageView iconImageView;
    TextView nameLabel;
}

}

以下是LogCat : Image

的图片

第45行是这一行：

    holder.iconImageView.setImageResource(R.drawable.ic_action_picture);

以下是布局的XML文件：

<ImageView
    android:id="@+id/messageIcon"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/message_list_item_vertical_margin"
    android:paddingBottom="@dimen/message_list_item_vertical_margin"
    android:src="@drawable/ic_action_picture" />

<TextView
    android:id="@+id/senderLabel"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerVertical="true"
    android:layout_toRightOf="@+id/messageIcon"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:paddingLeft="@dimen/activity_horizontal_margin" />

   </RelativeLayout>

我的可绘制文件夹中有图像，但我仍然收到此错误。任何人都可以建议，这个代码有什么问题。

Answer 1

在getView（）中缺少导致holder=null

的主要内容

public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;

    if (convertView == null) {
        convertView = LayoutInflater.from(mContext).inflate(R.layout.message_item, null);
        holder = new ViewHolder();
        holder.iconImageView = (ImageView)convertView.findViewById(R.id.messageIcon);
        holder.nameLabel = (TextView)convertView.findViewById(R.id.senderLabel);

        convertView.setTag(holder) // this line 
    }
    else {
        holder = (ViewHolder)convertView.getTag();
    }

按照@CommonsWare评论的所有说明进行操作

使用自定义列表时获取NPE

1 个答案: