ViewHolder模式获取控件空指针异常

最新推荐文章于 2024-03-28 18:42:14 发布

linyeban

最新推荐文章于 2024-03-28 18:42:14 发布

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分类专栏： Android

本文链接：https://blog.youkuaiyun.com/linyeban/article/details/52497923

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在使用ListView并集成BaseAdapter时，通过ViewHolder模式设置TextView内容时遇到了空指针异常。问题出在没有正确引用View。解决办法是在对应位置添加正确的View引用，避免空指针错误。

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在用ListView做开发的时候需要集成BaseAdapter类，复写其getView方法，这个想必大家都是知道的。今天在调试的时候遇到一个很折腾人的问题，在ViewHolder模式是用以下方式给TextView控件赋值时报空指针异常：

import engina.AppInfoProvider;

/**
 * Created by lin on 2016/9/9.
 */
public class AppManagerActivity extends Activity {
    private TextView tv_avail_rom;
    private TextView tv_avail_sd;
    private ListView lv_app_manager;
    private LinearLayout ll_loading;
    /**
     * 所有的应用程序包信息
     */
    private List<AppInfo> appInfos;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_app_manager);
        tv_avail_rom = (TextView) findViewById(R.id.tv_avail_rom);
        tv_avail_sd = (TextView) findViewById(R.id.tv_avail_sd);
        long sdsize = getAvailSpace(Environment.getExternalStorageDirectory().getAbsolutePath());
        long romsize = getAvailSpace(Environment.getDataDirectory().getAbsolutePath());
        tv_avail_sd.setText("SD卡可用空间:" + Formatter.formatFileSize(this, sdsize));
        tv_avail_rom.setText("内存可用空间" + Formatter.formatFileSize(this, romsize));

        lv_app_manager = (ListView) findViewById((R.id.lv_app_manager));
        ll_loading = (LinearLayout) findViewById(R.id.ll_loading);

        ll_loading.setVisibility(View.VISIBLE);
        new Thread() {
            public void run() {
                appInfos = AppInfoProvider.getAppInfos(AppManagerActivity.this);
                //加载listview的数据适配器
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        lv_app_manager.setAdapter(new AppMangerAdapter());
                        ll_loading.setVisibility(View.INVISIBLE);
                    }
                });
            }

            ;
        }.start();
    }
    static class ViewHolder {
        TextView tv_name;
        TextView tv_location;
        ImageView iv_icon;
    }

    private class AppMangerAdapter extends BaseAdapter {

        @Override
        public int getCount() {
            return appInfos.size();
        }

        @Override
        public Object getItem(int i) {
            return null;
        }

        @Override
        public long getItemId(int i) {
            return 0;
        }

        @Override
        public View getView(int i, View convertView, ViewGroup viewGroup) {
//            TextView tv=new TextView(getApplicationContext());
//            tv.setText(appInfos.get(i).toString());
//            return tv;
            View view;
            ViewHolder holder;
            if (convertView != null) {
                view = convertView;
                holder = (ViewHolder) view.getTag();
            } else {
                view = View.inflate(getApplicationContext(),R.layout.list_item_appinfo,null);
                holder = new ViewHolder();
                holder.iv_icon = (ImageView) view.findViewById(R.id.iv_app_icon);
                holder.tv_location = (TextView)findViewById(R.id.tv_app_location);//此处出现空指针
                holder.tv_name = (TextView)findViewById(R.id.tv_app_name);//此处出现空指针
                view.setTag(holder);
            }
            AppInfo appInfo = appInfos.get(i);
            holder.iv_icon.setImageDrawable(appInfo.getIcon());
            System.out.println("应用名称"+appInfo.getName());

            holder.tv_name.setText(appInfo.getName());

            if(appInfo.isInRom()){
                holder.tv_location.setText("手机内存");
            }else {
                holder.tv_location.setText("外部存储");
            }

            return view;
        }

    }


    /**
     * 获取某个目录的可用空间
     *
     * @param path
     * @return
     */
    private long getAvailSpace(String path) {
        StatFs statf = new StatFs(path);
        statf.getBlockCount();//获取分区的个数
        long size = statf.getBlockSize();//获取分区的大小
        long count = statf.getAvailableBlocks();//获取可用区块的个数
        return size * count;
    }
}

根据现象，百度了一下…… 结果，原来原因就少添加了一个View。出现指针那里修改成下面代码就可以了

holder.iv_icon = (ImageView) view.findViewById(R.id.iv_app_icon);
holder.tv_location = (TextView)view.findViewById(R.id.tv_app_location);
holder.tv_name = (TextView)view.findViewById(R.id.tv_app_name);