Question

我正在尝试使用 listview和arrayadapter 创建应用。我有一个自定义类（Word）和一个自定义适配器（WordAdapter）。通过运行此代码，应用程序崩溃 这是错误：

java.lang.NullPointerException：尝试调用虚方法'void 空对象引用上的android.view.View.setTag（java.lang.Object）'

以下代码：

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.ArrayList;

public class WordAdapter extends ArrayAdapter<Word> {

    //datastructure to hold two textviews, so that it can be reused rather than instantiating
    static class ViewHolder {
        TextView textView1;
        TextView textView2;
    }

    //sets up the arrayadapter
    //@param context : specify the context (e.g current activity)
    //@param words : list of words to populate the view (contains objects of custom word class)
    public WordAdapter(@NonNull Context context, @NonNull ArrayList<Word> words) {
        super(context, 0, words);
    }

    /*
    Needs to override when using custom arrayadapater.
    Called by the adapter class when populating data from data source into the view
    @param position : position of the data in the data source
    @param convertView : data from source is set as the data for this view
    @param parent : parent view to which convertview gets attached
     */
    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        ViewHolder viewHolder;

        View list_item_view = convertView;

        //checks if any reusable view is available
        //list_item_view = null if no reusable view is available
        if (list_item_view == null) {
            viewHolder = new ViewHolder();

            //convert the custom layout file into view object and inflate the parent with the view
            //returns the root of the custom layout file (if attachToRoot = false)
            //returns parent view to which the layout is to be attached (if attachToRoot = true)
            list_item_view = LayoutInflater.from(getContext())
                    .inflate(R.layout.list_item, parent, false);

            viewHolder.textView1 = (TextView) list_item_view.findViewById(R.id.miwok_text_view);
            viewHolder.textView2 = (TextView) list_item_view.findViewById(R.id.default_text_view);

            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        //get the data from the position
        Word word = getItem(position);

        //set the miwok word
        viewHolder.textView1.setText(word.getMiwokWord());

        //set the default word
        viewHolder.textView2.setText(word.getDefaultWord());

        //retrun the view to which data is to be placed
        return list_item_view;
    }

}

任何人都请帮忙。

Answer 1

你应该改变以下几行：

 list_item_view .setTag(viewHolder);

 viewHolder = (ViewHolder) list_item_view .getTag();

view.setTag（Object obj）抛出nullpointerexception

1 个答案: