在用ListView做開發的時候需要整合BaseAdapter類，複寫其getView方法，這個想必大家都是知道的。今天在除錯的時候遇到一個很折騰人的問題，在ViewHolder模式是用以下方式給TextView控制元件賦值時報空指標異常：

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;
/**
     * 所有的應用程式包資訊
     */
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卡可用空間:" + Formatter.formatFileSize(this, sdsize));
tv_avail_rom.setText("記憶體可用空間" + 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);
//載入listview的資料介面卡
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);//此處出現空指標
holder.tv_name = (TextView)findViewById(R.id.tv_app_name);//此處出現空指標
view.setTag(holder);
}
            AppInfo appInfo = appInfos.get(i);
holder.iv_icon.setImageDrawable(appInfo.getIcon());
System.out.println("應用名稱"+appInfo.getName());
holder.tv_name.setText(appInfo.getName());
            if(appInfo.isInRom()){
                holder.tv_location.setText("手機記憶體");
}else {
                holder.tv_location.setText("外部儲存");
}

            return view;
}

    }


    /**
     * 獲取某個目錄的可用空間
     *
     * @param path
* @return
*/
private long getAvailSpace(String path) {
        StatFs statf = new StatFs(path);
statf.getBlockCount();//獲取分割槽的個數
long size = statf.getBlockSize();//獲取分割槽的大小
long count = statf.getAvailableBlocks();//獲取可用區塊的個數
return size * count;
}
}

根據現象，百度了一下…… 結果，原來原因就少添加了一個View。出現指標那裡修改成下面程式碼就可以了

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);

參考部落格：http://blog.csdn.net/cheer_zhang/article/details/38057567