我遇到了无法解决的nullPointerException问题。有人可以帮忙吗？
my code:
package gsb.com;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.widget.TextView;
the main class
public class ActivitePrincipale extends Activity {
//Variables pour l'authentification
private TextView tv;
public static final int RESULT_Main = 1;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activite_principale);
//Authentification
//Appel de la page de Login
startActivityForResult(new Intent(ActivitePrincipale.this, Login.class), RESULT_Main);
//tv = new TextView(this);
//setContentView(tv);
}
//Procédure d'authentification
private void startup(Intent i)
{
// Récupère l'identifiant
int user = i.getIntExtra("userid",-1);
//Affiche les identifiants de l'utilisateur
tv.setText("UserID: "+String.valueOf(user)+" logged in");
}
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{
if(requestCode == RESULT_Main && resultCode == RESULT_CANCELED)
finish();
else
startup(data);
}
}
登录类
package gsb.com;
import gsb.com.R;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.protocol.HTTP;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.os.Looper;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class Login extends Activity
{
// Lien vers votre page php sur le serveur
private static final String UPDATE_URL = some ip
public ProgressDialog progressDialog;
private EditText UserEditText;
private EditText PassEditText;
private android.widget.Button button;
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
Log.i("Info","Dans Login - onCreate --------------");
//initialisation d'une progress bar
progressDialog = new ProgressDialog(this);
progressDialog.setMessage("Patientez svp...");
progressDialog.setIndeterminate(true);
progressDialog.setCancelable(false);
//recuperation des elements de la vue
UserEditText = (EditText)findViewById(R.id.username);
if (UserEditText == null) { Log.w("Info", "UserEditText est null --------------"); }
PassEditText = (EditText)findViewById(R.id.password);
if (PassEditText == null) { Log.w("Info", "PassEditText est null --------------"); }
button = (Button)findViewById(R.id.okbutton);
if (button == null) { Log.w("Info", "button est null --------------"); }
//definition du listener du bouton ok
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
int userSize = UserEditText.getText().length();
int passSize = PassEditText.getText().length();
//si les deux champs sont complétés
if(userSize > 0 && passSize > 0){
progressDialog.show();
String user = UserEditText.getText().toString();
String pass = PassEditText.getText().toString();
//appel de la fonction doLogin qui va appeler le script connect.php
doLogin(user,pass);
}
else {
createDialog("Erreur !!", "SVP Entrez un nom d'utilisateur et un mot de passe.");
}
}
});
button = (Button)findViewById(R.id.cancelbutton);
//creation du listener du bouton annuler pour sortir de l'appli
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
quit(false, null);
}
});
}
private void quit(boolean succes, Intent i){
//envoi d'un resultat qui va permettre de quitter l'appli
setResult((succes)? Activity.RESULT_OK : Activity.RESULT_CANCELED,i);
finish();
}
private void createDialog(String title, String text){
//affichage d'un popup
AlertDialog ad = new AlertDialog.Builder(this)
.setPositiveButton("Ok", null).setTitle(title).setMessage(text)
.create();
ad.show();
}
private void doLogin(final String login, final String pass){
final String pw = md5(pass);
//final String pw = pass;
//creation d'un thread
Thread t = new Thread(){
public void run(){
Looper.prepare();
//connexion au serveur pour communiquer avec le php
DefaultHttpClient client = new DefaultHttpClient();
HttpConnectionParams.setConnectionTimeout(client.getParams(),15000);
HttpResponse response;
HttpEntity entity;
try{
//on etablit un lien avec le script connect.php
HttpPost post = new HttpPost(UPDATE_URL);
List<NameValuePair> nvp = new ArrayList<NameValuePair>();
nvp.add(new BasicNameValuePair("username",login));
nvp.add(new BasicNameValuePair("password",pw));
post.setHeader("Content-Type", "application/x-www-form-urlencoded");
//passage des params login et password qui vont etre recup par le script php en Post
post.setEntity(new UrlEncodedFormEntity(nvp, HTTP.UTF_8));
//recup du resultat du script
response = client.execute(post);
entity = response.getEntity();
InputStream is = entity.getContent();
//appel d'une fonction pour traduire la reponse
read(is);
is.close();
if(entity != null){
entity.consumeContent();
}
}
catch(Exception e){
progressDialog.dismiss();
createDialog("Error", "Impossible d'etablir une connexion");
}
Looper.loop();
}
};
t.start();
}
private void read(InputStream inpStr){
//traduction du resultat du flux
SAXParserFactory spf = SAXParserFactory.newInstance();
SAXParser sp;
try{
sp = spf.newSAXParser();
XMLReader xr = sp.getXMLReader();
//classe definie plus bas
LoginContentHandler lch = new LoginContentHandler();
xr.setContentHandler(lch);
xr.parse(new InputSource(inpStr));
}
catch(ParserConfigurationException e){}
catch(SAXException e){}
catch(IOException e){}
}
private String md5(String in) {
MessageDigest digest;
try {
digest = MessageDigest.getInstance("MD5");
digest.reset();
digest.update(in.getBytes());
byte[] a = digest.digest();
int len = a.length;
StringBuilder sb = new StringBuilder(len << 1);
for (int i = 0; i < len; i++) {
sb.append(Character.forDigit((a[i] & 0xf0) >> 4, 16));
sb.append(Character.forDigit(a[i] & 0x0f, 16));
}
return sb.toString();
}
catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
return null;
}
private class LoginContentHandler extends DefaultHandler {
//Traite le retour du script connect.php
private boolean in_loginTag = false;
private int userID;
private boolean error_occured = false;
public void startElement(String n, String l, String q, Attributes a) throws SAXException {
if(l=="login"){
in_loginTag = true;
}
if(l=="error"){
progressDialog.dismiss();
switch(Integer.parseInt(a.getValue("value"))){
case 1:
createDialog("Error", "Impossible de se connecter à la base de données");
break;
case 2:
createDialog("Error", "Erreur dans la base de données, Table manquante");
break;
case 3:
createDialog("Error", "Login ou mot de passe invalide !");
break;
}
error_occured = true;
}
if(l=="user" && in_loginTag && a.getValue("id")!=""){
//si tout est ok on recup l'id de l'utilisateur
userID = Integer.parseInt(a.getValue("id"));
}
}
public void endElement(String n, String l, String q) throws SAXException {
//on renvoie l'id si tout est ok
if(l=="login"){
in_loginTag = false;
if(! error_occured){
progressDialog.dismiss();
Intent i = new Intent();
i.putExtra("userid", userID);
quit(true, i);
}
}
}
public void characters(char ch[], int start, int length){}
public void startDocument() throws SAXException{}
public void endDocument() throws SAXException{}
}
}
xml文件
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".ActivitePrincipale" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="14dp"
android:text="@string/connexion_form_title" />
<EditText
android:id="@+id/password"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/username"
android:layout_centerHorizontal="true"
android:layout_marginTop="25dp"
android:ems="10"
android:inputType="textPassword"
android:text="@string/password_text_field"/>
<EditText
android:id="@+id/username"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/textView1"
android:layout_centerHorizontal="true"
android:layout_marginTop="34dp"
android:inputType="text"
android:ems="10"
android:text="@string/username_text_field"/>
<Button
android:id="@+id/okbutton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/password"
android:layout_centerHorizontal="true"
android:layout_marginTop="66dp"
android:text="@string/connexion_button" />
<Button
android:id="@+id/cancelbutton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/okbutton"
android:layout_centerHorizontal="true"
android:layout_marginTop="30dp"
android:text="@string/cancel_button" />
</RelativeLayout>
the manifest
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="gsb.com"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="gsb.com.ActivitePrincipale"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name="gsb.com.Login" android:label="Login">
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
和错误日志
05-30 13:29:37.252: I/Info(712): Dans Login - onCreate --------------
05-30 13:29:37.272: W/Info(712): UserEditText est null --------------
05-30 13:29:37.272: W/Info(712): PassEditText est null --------------
05-30 13:29:37.282: W/Info(712): button est null --------------
05-30 13:29:37.304: D/AndroidRuntime(712): Shutting down VM
05-30 13:29:37.304: W/dalvikvm(712): threadid=1: thread exiting with uncaught exception (group=0x40015560)
05-30 13:29:37.342: E/AndroidRuntime(712): FATAL EXCEPTION: main
05-30 13:29:37.342: E/AndroidRuntime(712): java.lang.RuntimeException: Unable to start activity ComponentInfo{gsb.com/gsb.com.Login}: java.lang.NullPointerException
05-30 13:29:37.342: E/AndroidRuntime(712): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
05-30 13:29:37.342: E/AndroidRuntime(712): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
05-30 13:29:37.342: E/AndroidRuntime(712): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
05-30 13:29:37.342: E/AndroidRuntime(712): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
05-30 13:29:37.342: E/AndroidRuntime(712): at android.os.Handler.dispatchMessage(Handler.java:99)
05-30 13:29:37.342: E/AndroidRuntime(712): at android.os.Looper.loop(Looper.java:123)
05-30 13:29:37.342: E/AndroidRuntime(712): at android.app.ActivityThread.main(ActivityThread.java:3683)
05-30 13:29:37.342: E/AndroidRuntime(712): at java.lang.reflect.Method.invokeNative(Native Method)
05-30 13:29:37.342: E/AndroidRuntime(712): at java.lang.reflect.Method.invoke(Method.java:507)
05-30 13:29:37.342: E/AndroidRuntime(712): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-30 13:29:37.342: E/AndroidRuntime(712): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-30 13:29:37.342: E/AndroidRuntime(712): at dalvik.system.NativeStart.main(Native Method)
05-30 13:29:37.342: E/AndroidRuntime(712): Caused by: java.lang.NullPointerException
05-30 13:29:37.342: E/AndroidRuntime(712): at gsb.com.Login.onCreate(Login.java:67)
05-30 13:29:37.342: E/AndroidRuntime(712): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-30 13:29:37.342: E/AndroidRuntime(712): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
05-30 13:29:37.342: E/AndroidRuntime(712): ... 11 more
答案 0 :(得分：5)
你必须在超级之后首先使用setContentview(R.layout.XXXX)，然后才能使用资源。另外，你会得到空指针异常..
在Login Activity ....中缺少设置内容视图。
答案 1 :(得分：3)
您正尝试将相同的按钮变量设置为布局上的两个不同按钮：
button = (Button)findViewById(R.id.okbutton);
button = (Button)findViewById(R.id.cancelbutton);
您需要为这些创建两个单独的变量。
编辑经过多次辩论，我再次尝试了一些代码，并意识到问题出在哪里。
我按钮设置如下：
button = (Button) findViewById(R.id.ok);
button = (Button) findViewById(R.id.cancel);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v){
//stuff
}
});
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v){
// other stuff
}
});
这样不行!!!然而经过多次辩论后，我想尝试以下其他方法：
button = (Button) findViewById(R.id.ok);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v){
//stuff
}
});
button = (Button) findViewById(R.id.cancel);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v){
// other stuff
}
});
另一方面，这是有效的。
答案 2 :(得分：2)
您的问题或至少一个问题是您没有在Login中夸大布局。因此，您尝试使用的任何视图（BUtton，EditText等等）将为null
在onCreate()调用setContentView(R.layout.yourLayout);之前尝试设置Views之类
UserEditText = (EditText)findViewById(R.id.username);
Views内的Layout存在null，直到您使用layout或inflater对setContentView(...);进行充气后才会{{1}} }
此外，自从你是新的
以来，关于网站的一些事情这些不是真正的问题，但可以帮助您获得更好/更快的答案。
答案 3 :(得分：1)
我注意到您的Login活动中没有setContentView。 通常，如果人们在调用setContentView之前调用它，则会使用findViewById（...）获取空指针错误。在您的情况下，您甚至没有setContentView（）。
答案 4 :(得分：0)
如果你的OK按钮没有响应点击，那么垃圾收集器可能会扫描监听器实例。
将您的侦听器创建为类级属性：
private OnClickListener okListener = new View.OnClickListener() { ... };
private OnClickListener cancelListener = new View.OnClickListener() { ... };
然后在onCreate（）中分配它们：
((Button)findViewById(R.id.okbutton)).setOnClickListener(okListener);
((Button)findViewById(R.id.cancelbutton)).setOnClickListener(cancelListener );
由于侦听器在活动内部有引用，因此不会收集垃圾。我在一个单独的线程上启动媒体播放器时遇到了类似的问题。玩家被杀了，因为我没有坚持对线程的引用，所以垃圾收集器看到了一个未引用的对象树并将其清理干净。