Java 我的android应用程序崩溃，出现空指针异常
我的应用程序有问题，当我运行“showContest”活动时，我的应用程序崩溃并出现以下错误：Java 我的android应用程序崩溃，出现空指针异常,java,android,crash,Java,Android,Crash,我的应用程序有问题，当我运行“showContest”活动时，我的应用程序崩溃并出现以下错误： 03-27 11:18:49.038: E/AndroidRuntime(5279): FATAL EXCEPTION: main 03-27 11:18:49.038: E/AndroidRuntime(5279): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{ru.artemzin.android
03-27 11:18:49.038: E/AndroidRuntime(5279): FATAL EXCEPTION: main
03-27 11:18:49.038: E/AndroidRuntime(5279): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{ru.artemzin.android.tutorials.listfragmentexample/time2win.android.ShowContest}: java.lang.NullPointerException
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.os.Handler.dispatchMessage(Handler.java:99)
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.os.Looper.loop(Looper.java:137)
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.app.ActivityThread.main(ActivityThread.java:5039)
03-27 11:18:49.038: E/AndroidRuntime(5279): at java.lang.reflect.Method.invokeNative(Native Method)
03-27 11:18:49.038: E/AndroidRuntime(5279): at java.lang.reflect.Method.invoke(Method.java:511)
03-27 11:18:49.038: E/AndroidRuntime(5279): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-27 11:18:49.038: E/AndroidRuntime(5279): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-27 11:18:49.038: E/AndroidRuntime(5279): at dalvik.system.NativeStart.main(Native Method)
03-27 11:18:49.038: E/AndroidRuntime(5279): Caused by: java.lang.NullPointerException
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:161)
03-27 11:18:49.038: E/AndroidRuntime(5279): at time2win.android.User.getUserId(User.java:10)
03-27 11:18:49.038: E/AndroidRuntime(5279): at time2win.android.ShowContest.<init>(ShowContest.java:53)
03-27 11:18:49.038: E/AndroidRuntime(5279): at java.lang.Class.newInstanceImpl(Native Method)
03-27 11:18:49.038: E/AndroidRuntime(5279): at java.lang.Class.newInstance(Class.java:1319)
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
03-27 11:18:49.038: E/AndroidRuntime(5279): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
03-27 11:18:49.038: E/AndroidRuntime(5279): ... 11 more
谢谢在崩溃堆栈跟踪之前，您会发现一条日志消息，如
AndroidRuntime D关闭VM我的猜测是：JIT是有责任的，您不能做任何反对它的事情（而且这并不重要）。您使用共享首选项初始化变量太早了，没有有效的上下文 因此，而不是
publicstringid=User.getUserId（this）id=User.getUserId（getApplicationContext（））初始化onCreate
方法中的变量
还初始化onCreate
完整堆栈后跟踪中的其他变量。是否已在清单文件中添加所有活动？使用findviewbyId（）获取引用时，检查所有视图是否不为null；你发布了错误的stacktrace我发布了一个新的stacktrace（last）嗨，谢谢你的帮助，但是我的应用程序在启动时加载了一些数据（显示一个splashscreen），在打开MainActivity之后，在这个活动中我们可以找到一个ListView，一切正常，但是当我单击列表视图时，ShowContest的活动更改为空指针并崩溃。。。但如果我把id的核心值，pass和idcompetite所有的工作。。。所有外部数据（来自sharepreference或intent）可能会使我的应用程序崩溃…那么您发布的stacktrace是错误的。你完全确定这是stacktrace logcat向你展示的最后一个stacktrace吗？我发布了一个新的stacktrace这是最后一个stack Trace查看Andrea的答案，请下次确保发布正确的stacktrace，为你和我节省了不少时间…我正要写同样的东西@Bastien您不应该将字符串与==
进行比较，而应该使用equals（）
谢谢这是解决方案，很抱歉我的java:x水平很低
package myapp.android;
import java.io.IOException;
import java.io.InputStream;
import java.io.Serializable;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import ru.artemzin.android.tutorials.listfragmentexample.R;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Color;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
public class ShowContest extends Activity {
public static String URL = null;
public static String title = null;
public static String subtitle = null;
public static String description = null;
public static String won = null;
public static String color = null;
public static String toDisplay = null;
public static String arrayPost = null;
public static int pos;
public static int nextPosInt;
public static int backPosInt;
public static int dataSize;
public static ArrayList<String> data = null;
public String idContest = (String) getIntent().getSerializableExtra("id");
public String pass = User.getUserPass(this);
public String id = User.getUserId(this);
ImageView imageView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
System.out.println("Create");
String etat = null;
String content = null;
if (getIntent().getSerializableExtra("participate_sending") != null)
{
Document docStat = null;
System.out.println("In da IF");
String xmlStat = new XMLfunctionsBack().doInBackground("urltoxml);
System.out.println("XML request done");
docStat = XMLfunctions.XMLfromString(xmlStat);
System.out.println("parsing done");
NodeList nodesParticipate = docStat.getElementsByTagName("respond");
for (int i = 0; i < nodesParticipate.getLength(); i++) {
Element e = (Element)nodesParticipate.item(i);
etat = XMLfunctions.getValue(e, "name");
content = XMLfunctions.getValue(e, "content");
}
if (etat == "ERREUR")
{
Toast.makeText(this, content, Toast.LENGTH_LONG).show();
}
if (etat == "OK")
{
Toast.makeText(this, content, Toast.LENGTH_LONG).show();
}
else
Toast.makeText(this, "Strange ERROR", Toast.LENGTH_LONG).show();
}
System.out.println("After da IF");
/*********************Fetch Contest content*******************/
//Needed for arrow navigation
final Serializable posSerialize = getIntent().getSerializableExtra("pos");
pos = Integer.parseInt((String) getIntent().getSerializableExtra("pos"));
data = getIntent().getStringArrayListExtra("data");
nextPosInt = pos +1;
backPosInt = pos -1;
dataSize = data.size() -1;
String xml = new XMLfunctionsBack().doInBackground(urltoyml);
Document doc = XMLfunctions.XMLfromString(xml);
NodeList nodes = doc.getElementsByTagName("contest");
for (int i = 0; i < nodes.getLength(); i++) {
Element e = (Element)nodes.item(i);
URL = "urltoimage);
title = XMLfunctions.getValue(e, "name");
subtitle = XMLfunctions.getValue(e, "subtitle");
description = XMLfunctions.getValue(e, "description");
won = XMLfunctions.getValue(e, "description");
color = "#" + XMLfunctions.getValue(e, "color");
toDisplay = XMLfunctions.getValue(e, "text_to_display");
}
setContentView(R.layout.show_contest);
imageView = (ImageView) findViewById(R.id.imageView);
TextView titleText = (TextView) findViewById(R.id.textView1);
titleText.setText(title);
titleText.setTextColor(Color.parseColor(color));
TextView subtitleText = (TextView) findViewById(R.id.textView2);
subtitleText.setText(subtitle);
TextView descriptionText = (TextView) findViewById(R.id.textView3);
descriptionText.setText(description);
TextView toDisplayText = (TextView) findViewById(R.id.todisplay);
toDisplayText.setText(toDisplay);
toDisplayText.setTextColor(Color.parseColor(color));
// Create an object for subclass of AsyncTask
GetXMLTask task = new GetXMLTask();
// Execute the task
task.execute(new String[] { URL });
Button button = (Button) findViewById(R.id.participer);
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
Intent intent = new Intent(getBaseContext(), Participate.class);
intent.putExtra("id",idContest);
intent.putExtra("pos",posSerialize);
intent.putStringArrayListExtra( "data", data);
startActivity(intent);
}
});
}
/************************Top Menu nav*****************************/
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.activity_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_forward:
if (dataSize > pos)
{
String nextPos = String.valueOf(nextPosInt);
String next = data.get(nextPosInt);
Intent intent = new Intent(this, ShowContest.class);
intent.putExtra("id", next);
intent.putExtra("pos",nextPos);
intent.putStringArrayListExtra( "data", data);
startActivity(intent);
}
else
{
Toast.makeText(this, "Vous êtes déjà au dernier concour", Toast.LENGTH_LONG)
.show();
}
break;
case R.id.action_back:
if (0 < pos)
{
String backPos = String.valueOf(backPosInt);
String back = data.get(backPosInt);
Intent intent = new Intent(this, ShowContest.class);
intent.putExtra("id", back);
intent.putExtra("pos",backPos);
intent.putStringArrayListExtra( "data", data);
startActivity(intent);
}
else
{
Toast.makeText(this, "Vous êtes déjà au premier concour", Toast.LENGTH_LONG)
.show();
}
break;
case R.id.boutique:
Intent intentBoutique = new Intent(this, MainActivity.class);
intentBoutique.putExtra("type", "1");
startActivity(intentBoutique);
case R.id.restaurant:
Intent intentRestaurant = new Intent(this, MainActivity.class);
intentRestaurant.putExtra("type", "2");
startActivity(intentRestaurant);
case R.id.nightlife:
Intent intentNightlife = new Intent(this, MainActivity.class);
intentNightlife.putExtra("type", "3");
startActivity(intentNightlife);
case R.id.loisir:
Intent intent = new Intent(this, MainActivity.class);
intent.putExtra("type", "4");
startActivity(intent);
case R.id.evenement:
Intent intentEvenement = new Intent(this, MainActivity.class);
intentEvenement.putExtra("type", "5");
startActivity(intentEvenement);
default:
break;
}
return true;
}
/************************Image part******************************/
private class GetXMLTask extends AsyncTask<String, Void, Bitmap> {
@Override
protected Bitmap doInBackground(String... urls) {
Bitmap map = null;
for (String url : urls) {
map = downloadImage(url);
}
return map;
}
// Sets the Bitmap returned by doInBackground
@Override
protected void onPostExecute(Bitmap result) {
imageView.setImageBitmap(result);
}
// Creates Bitmap from InputStream and returns it
private Bitmap downloadImage(String url) {
Bitmap bitmap = null;
InputStream stream = null;
BitmapFactory.Options bmOptions = new BitmapFactory.Options();
bmOptions.inSampleSize = 1;
try {
stream = getHttpConnection(url);
bitmap = BitmapFactory.
decodeStream(stream, null, bmOptions);
stream.close();
} catch (IOException e1) {
e1.printStackTrace();
}
return bitmap;
}
// Makes HttpURLConnection and returns InputStream
private InputStream getHttpConnection(String urlString)
throws IOException {
InputStream stream = null;
URL url = new URL(urlString);
URLConnection connection = url.openConnection();
try {
HttpURLConnection httpConnection = (HttpURLConnection) connection;
httpConnection.setRequestMethod("GET");
httpConnection.connect();
if (httpConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {
stream = httpConnection.getInputStream();
}
} catch (Exception ex) {
ex.printStackTrace();
}
return stream;
}
}
}
public class User {
public final static String PREFS_NAME = "UserData";
public static String getUserId(Context context)
{
SharedPreferences settings = context.getSharedPreferences(PREFS_NAME, 0);
String id = settings.getString("id", "");
return id;
}
public static String getUserPass(Context context)
{
SharedPreferences settings = context.getSharedPreferences(PREFS_NAME, 0);
String pass = settings.getString("pass", "");
return pass;
}
}