问题描述

当设置 setText 时 Custom listview 出错

我创建了一个Custom listview，有一个image text 和 checkbox ，当我想设置一个值时，却获得一个NUll Pointer Exception异常。如果我不设置一个值如何获得默认的list？

class PInfo {    String appname = """";    String pname = """";    String versionName = """";    int versionCode = 0;    int icon; } public class InstalledApps extends Activity{    private static LayoutInflater inflater=null;private ListView listview;private Activity activity;List<PInfo> installedApps = new ArrayList<PInfo>();@Overrideprotected void onCreate(Bundle savedInstanceState) {    // TODO Auto-generated method stub    super.onCreate(savedInstanceState);    setContentView(R.layout.applist);    activity = this;    listview = (ListView)findViewById(R.id.listView1);    PackageManager pm = getPackageManager();    List<ApplicationInfo> packages = pm.getInstalledApplications(PackageManager.GET_META_DATA);    for(ApplicationInfo app : packages) {        PInfo newInfo = new PInfo();            newInfo.appname = (String) app.loadLabel(pm);            newInfo.pname = app.packageName;        if((app.flags & ApplicationInfo.FLAG_UPDATED_SYSTEM_APP) == 1){                         installedApps.add(newInfo);        } else if ((app.flags & ApplicationInfo.FLAG_SYSTEM) == 1) {            installedApps.add(newInfo);        } else {            installedApps.add(newInfo);         }    }    InstalledAppsAdapter iap = new InstalledAppsAdapter(this installedApps);listview.setAdapter(iap);}}class InstalledAppsAdapter extends BaseAdapter{private Activity activity;private static LayoutInflater inflater=null;List<PInfo> installedApps = new ArrayList<PInfo>();ListView listview; public InstalledAppsAdapter(Activity a List<PInfo> b) {   // TODO Auto-generated constructor stub    installedApps = b;    activity = a;    inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);    listview = (ListView)activity.findViewById(R.id.listView1);}@Overridepublic int getCount() {    // TODO Auto-generated method stub    return installedApps.size();}@Overridepublic Object getItem(int arg0) {    // TODO Auto-generated method stub    return arg0;}@Overridepublic long getItemId(int arg0) {    // TODO Auto-generated method stub    return arg0;}@Overridepublic View getView(int arg0 View arg1 ViewGroup arg2) {    // TODO Auto-generated method stub    View customView = arg1;    ViewHolder holder;    if(arg1 == null){        customView = inflater.inflate(R.layout.listrow null);    holder = new ViewHolder();    holder.iv = (ImageView)customView.findViewById(R.id.imageView1);    holder.tv = (TextView) customView.findViewById(R.id.textView2);    holder.cb = (CheckBox)customView.findViewById(R.id.checkBox1);    }else{        holder = (ViewHolder)customView.getTag();    }    PInfo pinfo = installedApps.get(arg0);    holder.tv.setText(""""+pinfo.appname);    return customView;}static class ViewHolder{    ImageView iv;    CheckBox cb;    TextView tv;}

看起来像findViewById(R.id.textView1)返回null。什么问题呢?

解决方案

好像是一般下面这么写吧，你的有点怪，而且你也少了convertView.setTag(holder);这个动作

 public View getView(int position View convertView ViewGroup parent) {            System.out.println(""getView "" + position + "" "" + convertView);            ViewHolder holder = null;            if (convertView == null) {                convertView = mInflater.inflate(R.layout.item1 null);                holder = new ViewHolder();                holder.textView = (TextView)convertView.findViewById(R.id.text);                convertView.setTag(holder);            } else {                holder = (ViewHolder)convertView.getTag();            }            holder.textView.setText(mData.get(position));            return convertView;        }