我从远程数据库读取要在ListView中写入包含imageview和文本的女巫。
我有java.lang.NullPointerException错误 我试图解决它，但我无法解决。
在doInBackground方法的for循环中，数组String是可以的，我可以在logcat中写出结果但是在for循环之外我不能。
感谢。
package com.example.alztrimakis;
import java.util.ArrayList;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;
import android.widget.Toast;
public class contact extends Activity {
ListView list;
LazyImageLoadAdapter adapter;
JSONParser jParser = new JSONParser();
private static final String TAG_nom = "nom";
private static final String TAG_prenom = "prenom";
private static final String TAG_relation = "relation";
private static final String TAG_SUCCESS = "success";
private static final String TAG_photo = "photo";
private static final String TAG_pers = "idpersonne";
SharedPreferences pref;
String [] tabphoto, tabnom, tabprenom, tabrelation, tabidpers;
private ProgressDialog pDialog;
String idp ;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.contact);
list=(ListView)findViewById(R.id.listViewcontact);
loadReps verif = new loadReps();
verif.execute();
Log.d("load","ok");
Log.d("tabphoto",tabphoto.toString());
Log.d("tabnom",tabnom.toString());
Log.d("tabprenom",tabprenom.toString());
Log.d("tabrelation",tabrelation.toString());
Log.d("tabidpers",tabidpers.toString());
// Create custom adapter for listview
adapter= new LazyImageLoadAdapter(this, tabphoto, tabnom, tabprenom, tabrelation);
Log.d("adapter","ok");
//Set adapter to listview
list.setAdapter(adapter);
}
public void onItemClick(int mPosition)
{
String tempValues = tabphoto[mPosition];
String idperss = tabidpers[mPosition];
Toast.makeText(contact.this,
"Image URL : "+tempValues+" dest "+idperss,
Toast.LENGTH_LONG)
.show();
}
// Image urls used in LazyImageLoadAdapter.java file
class loadReps extends AsyncTask<String, String, String> {
JSONObject tt;
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(contact.this);
pDialog.setMessage("Chargement...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
Log.d("onpreExec","ok");
}
@Override
protected String doInBackground(String... args) {
Log.d("back","ok");
pref = getSharedPreferences("memtrimakis",0);
idp = pref.getString("idpatient", "no");
if (idp != "no")
{
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("idpatient",idp));
IWebServices webServices = new WebServices();
try {
String result = webServices.getResult("affcontacts.php",nameValuePairs);
JSONObject json = new JSONObject(result);
Log.d("rep:", json.toString());
int success = json.getInt(TAG_SUCCESS);
selectip ipaddresse =new selectip();
if (success == 1) {
tabphoto = new String[json.length()];
tabnom = new String[json.length()];
tabprenom = new String[json.length()];
tabrelation = new String[json.length()];
tabidpers = new String[json.length()];
for (int i=0; i<json.length();i++)
{
tt = (JSONObject) json.get(String.valueOf(i));
tabphoto[i] = ipaddresse.adresseip().toString()+"img/"+tt.getString(TAG_photo);
tabnom[i]= tt.getString(TAG_nom);
tabprenom[i]= tt.getString(TAG_prenom);;
tabrelation[i]= tt.getString(TAG_relation);
tabidpers[i]= tt.getString(TAG_pers);
}
}
}
catch (Exception e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onPostExecute(String file_url) {
Log.d("post","ok");
runOnUiThread(new Runnable() {
@Override
public void run() {
for (int j=0; j<tabphoto.length;j++)
{Log.d("tabphotob"+j,tabphoto[j]);}
}
});
if(pDialog != null)
pDialog.dismiss();
}
}
}
这是logcat
05-17 16:35:39.665: E/AndroidRuntime(2865): FATAL EXCEPTION: main
05-17 16:35:39.665: E/AndroidRuntime(2865): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.alztrimakis/com.example.alztrimakis.contact}: java.lang.NullPointerException
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.os.Handler.dispatchMessage(Handler.java:99)
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.os.Looper.loop(Looper.java:137)
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.app.ActivityThread.main(ActivityThread.java:5103)
05-17 16:35:39.665: E/AndroidRuntime(2865): at java.lang.reflect.Method.invokeNative(Native Method)
05-17 16:35:39.665: E/AndroidRuntime(2865): at java.lang.reflect.Method.invoke(Method.java:525)
05-17 16:35:39.665: E/AndroidRuntime(2865): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
05-17 16:35:39.665: E/AndroidRuntime(2865): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-17 16:35:39.665: E/AndroidRuntime(2865): at dalvik.system.NativeStart.main(Native Method)
05-17 16:35:39.665: E/AndroidRuntime(2865): Caused by: java.lang.NullPointerException
05-17 16:35:39.665: E/AndroidRuntime(2865): at com.example.alztrimakis.contact.onCreate(contact.java:47)
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.app.Activity.performCreate(Activity.java:5133)
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-17 16:35:39.665: E/AndroidRuntime(2865): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
05-17 16:35:39.665: E/AndroidRuntime(2865): ... 11 more
答案 0 :(得分：1)
异步任务是异步的。当execute()返回时，结果不可用，当您尝试访问未初始化的tabphoto数组时，您的NPE就会出现。
将使用异步任务结果的代码移动到任务onPostExecute()。
答案 1 :(得分：0)
NPE，因为在分配到适配器之前，tabphoto，tabnom，tabprenom，tabrelation数组都没有初始化。发生这种情况是因为Asynctasks是异步错误，在您尝试访问结果时可能仍在运行。确保在onPostExecute（）中构造适配器，如下所示：
package com.example.alztrimakis;
import java.util.ArrayList;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;
import android.widget.Toast;
public class contact extends Activity {
ListView list;
LazyImageLoadAdapter adapter;
JSONParser jParser = new JSONParser();
private static final String TAG_nom = "nom";
private static final String TAG_prenom = "prenom";
private static final String TAG_relation = "relation";
private static final String TAG_SUCCESS = "success";
private static final String TAG_photo = "photo";
private static final String TAG_pers = "idpersonne";
SharedPreferences pref;
String [] tabphoto, tabnom, tabprenom, tabrelation, tabidpers;
private ProgressDialog pDialog;
String idp ;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.contact);
list=(ListView)findViewById(R.id.listViewcontact);
loadReps verif = new loadReps();
verif.execute();
Log.d("load","ok");
Log.d("tabphoto",tabphoto.toString());
Log.d("tabnom",tabnom.toString());
Log.d("tabprenom",tabprenom.toString());
Log.d("tabrelation",tabrelation.toString());
Log.d("tabidpers",tabidpers.toString());
}
public void onItemClick(int mPosition)
{
String tempValues = tabphoto[mPosition];
String idperss = tabidpers[mPosition];
Toast.makeText(contact.this,
"Image URL : "+tempValues+" dest "+idperss,
Toast.LENGTH_LONG)
.show();
}
// Image urls used in LazyImageLoadAdapter.java file
class loadReps extends AsyncTask<String, String, String> {
JSONObject tt;
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(contact.this);
pDialog.setMessage("Chargement...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
Log.d("onpreExec","ok");
}
@Override
protected String doInBackground(String... args) {
Log.d("back","ok");
pref = getSharedPreferences("memtrimakis",0);
idp = pref.getString("idpatient", "no");
if (idp != "no")
{
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("idpatient",idp));
IWebServices webServices = new WebServices();
try {
String result = webServices.getResult("affcontacts.php",nameValuePairs);
JSONObject json = new JSONObject(result);
Log.d("rep:", json.toString());
int success = json.getInt(TAG_SUCCESS);
selectip ipaddresse =new selectip();
if (success == 1) {
tabphoto = new String[json.length()];
tabnom = new String[json.length()];
tabprenom = new String[json.length()];
tabrelation = new String[json.length()];
tabidpers = new String[json.length()];
for (int i=0; i<json.length();i++)
{
tt = (JSONObject) json.get(String.valueOf(i));
tabphoto[i] = ipaddresse.adresseip().toString()+"img/"+tt.getString(TAG_photo);
tabnom[i]= tt.getString(TAG_nom);
tabprenom[i]= tt.getString(TAG_prenom);;
tabrelation[i]= tt.getString(TAG_relation);
tabidpers[i]= tt.getString(TAG_pers);
}
}
}
catch (Exception e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onPostExecute(String file_url) {
Log.d("post","ok");
runOnUiThread(new Runnable() {
@Override
public void run() {
for (int j=0; j<tabphoto.length;j++)
{Log.d("tabphotob"+j,tabphoto[j]);}
}
});
// Create custom adapter for listview
adapter= new LazyImageLoadAdapter(contact.this, tabphoto, tabnom, tabprenom, tabrelation);
Log.d("adapter","ok");
//Set adapter to listview
list.setAdapter(adapter);
if(pDialog != null)
pDialog.dismiss();
}
}
}