【发布时间】：2013-08-20 19:15:13
【问题描述】：
我正在从数据库中读取一些记录并将它们加载到ListView。 ListView 由 CheckBox 和 TextView 组成。加载通过AsyncTask 完成。这部分应用程序运行良好。
下一步是根据数据库中的一些标志自动检查一些复选框，这里我遇到了问题。我正在尝试检查onPostExecute() 中的那些项目，然后我收到关于NullPointerException 的错误。例如，如果我从按钮小部件的setOnClickListener() 执行相同操作，则它可以正常工作。
问题是如何检查ListView 是否已填充，复选框和TextView 是否已加载并在屏幕上可见？
我不知道它是否会帮助程序中断的代码部分看起来像：
for (j=0; j<3; j++)
{
LinearLayout itemLayout = (LinearLayout)listView.getChildAt(j); // Find by under LinearLayout
CheckBox checkbox = (CheckBox)itemLayout.findViewById(R.id.ColChk);
for (k=0; k<rbmjere.size(); k++)
{
if (checkbox.getTag().toString() == rbmjere.get(k).toString())
{
checkbox.setChecked(true);
}
}
}
它在那一行中断：
LinearLayout itemLayout = (LinearLayout)listView.getChildAt(j);
我必须提到，这仅在我手动按下运行代码以自动检查框的按钮时才有效，并且仅在加载所有数据时才有效。
这是我的代码：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_spckontrola_update);
listView = (ListView)findViewById(R.id.listView1);
btnPohrani = (Button)findViewById(R.id.btnPohrani);
btnProvjeri = (Button)findViewById(R.id.btnProvjeri);
btnProvjeri.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
new loadSPCKontrole().execute("FCN");
}
});
MyArrList = new ArrayList<HashMap<String, String>>();
public void fillData()
{
SimpleAdapter listadapter = new SimpleAdapter(this, MyArrList, R.layout.activity_list_row,
new String[] {"OpisMjere", "RbMjere"}, new int[] {R.id.ColOpis, R.id.ColCode});
listView = (ListView)findViewById(R.id.listView1);
listView.setAdapter(listadapter);
}
private class loadSPCKontrole extends AsyncTask<String, Void, Void>
{
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(SPCUpdate.this);
pDialog.setMessage("Loading in progress ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(String... params) {
HashMap<String, String> map;
String k = params[0].toString();
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("sIDKategorija", k));
try
{
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://192.168.16.48" + "/spc/get_spcmjere.php");
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}
catch(Exception e)
{
Log.e("log_tag", "Error in http connection "+ e.toString());
}
try
{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"UTF-8"),8);
sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line="0";
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}
catch(Exception e)
{
Log.e("log_tag", "Error converting result " + e.toString());
}
int ct_id;
String ct_name;
try
{
jArray = new JSONArray(result);
JSONObject json_data=null;
for(int i=0;i<jArray.length();i++){
json_data = jArray.getJSONObject(i);
ct_id=json_data.getInt("RbMjere");
ct_name=json_data.getString("OpisMjere");
map = new HashMap<String, String>();
map.put("RbMjere", String.valueOf(ct_id));
map.put("OpisMjere", ct_name);
MyArrList.add(map);
}
}
catch(JSONException e1)
{
Log.e("Greška konvertiranja", e1.toString());
}
catch (ParseException e1)
{
e1.printStackTrace();
}
return null;
}
protected void onPostExecute(Void result)
{
super.onPostExecute(result);
fillData();
listView.setAdapter(new SPCMjereAdapter(SPCUpdate.this));
pDialog.dismiss();
}
}
public class SPCMjereAdapter extends BaseAdapter
{
private Context context;
public SPCMjereAdapter(Context c)
{
context = c;
}
public int getCount() {
return MyArrList.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(final int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null) {
convertView = inflater.inflate(R.layout.activity_list_row, null);
}
// ColID
TextView txtOpis = (TextView) convertView.findViewById(R.id.ColOpis);
txtOpis.setText(MyArrList.get(position).get("OpisMjere") +".");
// ColCode
TextView txtRbMjere = (TextView) convertView.findViewById(R.id.ColCode);
txtRbMjere.setText(MyArrList.get(position).get("RbMjere"));
// ColChk
CheckBox Chk = (CheckBox) convertView.findViewById(R.id.ColChk);
Chk.setTag(MyArrList.get(position).get("RbMjere"));
return convertView;
}
}
这是我如何获取应检查的项目的代码：
DB objDB = new DB();
ArrayList<Integer> rbmjere = objDB.getCheckedSPC(ID);
int k=0;
int j=0;
for (j=0; j<MyArrList.size(); j++)
{
LinearLayout itemLayout = (LinearLayout)listView.getChildAt(j); // Find by under LinearLayout
CheckBox checkbox = (CheckBox)itemLayout.findViewById(R.id.ColChk);
for (k=0; k<rbmjere.size(); k++)
{
if (checkbox.getTag().toString() == rbmjere.get(k).toString())
{
checkbox.setChecked(true);
}
}
}
上面的代码仅在 listview 填充了项目并且此代码位于 OnClickListener() 下时才有效，但如果我从 onPostExecute 运行它则不起作用，因为似乎未加载 listview 中的所有行。所以我的问题是，当所有行的加载完成时，我应该怎么做才能获取信息，然后根据我从数据库中获得的数据检查哪些项目应该被检查？
【问题讨论】：
-
向我们展示你初始化listView的代码
-
你不应该那样使用你的列表视图。使用选择的 listadapter 来维护您的 db 数据（例如光标适配器）和 flag/unflag/setText 等，基于您的适配器 getView
标签： android android-asynctask android-checkbox