我试图让我的Android应用程序与php网站一起工作。 我有数据库存储有关用户的信息，如用户ID，密码等。 但是当我从mainactivity应用程序中单击登录按钮时停止。
我的login.java如下
public class Login extends Activity {
Button home,login;
EditText uname,pword;
Context context;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
getActionBar().setDisplayHomeAsUpEnabled(true);
addListenerOnHome();
addListenerOnBtnlogin(); //this is line 42
uname = (EditText) findViewById(R.id.txtuserid);
pword = (EditText) findViewById(R.id.txtuserpass);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_login, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
public void addListenerOnHome() {
final Context context = this;
home = (Button)findViewById(R.id.btnhome);
home.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(context,MainActivity.class);
startActivity(intent);
}
});
}
public void addListenerOnBtnlogin() {
context = this;
final String username = uname.getText().toString(); //this is line 79
final String password = pword.getText().toString();
login = (Button)findViewById(R.id.btnlogin);
login.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Thread t = new Thread() {
public void run() {
postLoginData(username,password);
}
};
t.start();
}
});
}
private void postLoginData(String username,String password) {
try {
// Create a new HttpClient and Post Header
HttpClient httpclient = new DefaultHttpClient();
Log.e("Response-->", "after httpclient");
HttpPost httppost = new HttpPost("http://10.0.2.2/dealnow/login.php");
Log.e("Response-->", "after httppost");
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
nameValuePairs.add(new BasicNameValuePair("username", username));
nameValuePairs.add(new BasicNameValuePair("password", password));
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
Log.e("Responce-->", "after using the list name pair");
// Execute HTTP Post Request
Log.w("SENCIDE", "Execute HTTP Post Request");
HttpResponse response = httpclient.execute(httppost);
Log.e("Responce-->", "after execute the http response");
String str = EntityUtils.toString(response.getEntity(), HTTP.UTF_8);
if (str.toString().equalsIgnoreCase("true")) {
runOnUiThread(new Runnable() {
public void run() {
Intent intent = new Intent(context,MainActivity.class);
startActivity(intent);
}
});
} else {
runOnUiThread(new Runnable() {
public void run() {
//notlogged in
}
});
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
和login.php是
<?php
$host="localhost"; // Host name
$username="root"; // Mysql username
$password=""; // Mysql password
$db_name="user"; // Database name
$tbl_name="user_det"; // Table name
// Connect to server and select databse.
mysql_connect("$host","$username", "$password")or die("cannot connect");
mysql_select_db("$db_name")or die("cannot select DB");
// username and password sent from form
$myusername=$_POST['username'];
$mypassword=$_POST['password'];
// To protect MySQL injection
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);
$sql="SELECT * FROM $tbl_name WHERE user_id='$myusername' and
app_pass='$mypassword'";
$result=mysql_query($sql);
// Mysql_num_row is counting table row
$count=mysql_num_rows($result);
// If result matched $myusername and $mypassword, table row must be 1 row
if($count==1){
echo "true";
}
else {
echo "Login Failed";
}
?>
和logcat显示
04-29 03:16:11.355: D/dalvikvm(454): GC_FOR_ALLOC freed 30K, 3% free 7683K/7879K, paused 56ms
04-29 03:16:11.365: I/dalvikvm-heap(454): Grow heap (frag case) to 8.065MB for 495616-byte allocation
04-29 03:16:11.546: D/dalvikvm(454): GC_FOR_ALLOC freed <1K, 3% free 8166K/8391K, paused 83ms
04-29 03:16:11.765: D/dalvikvm(454): GC_CONCURRENT freed 1K, 3% free 8173K/8391K, paused 5ms+14ms
04-29 03:16:11.805: D/AndroidRuntime(454): Shutting down VM
04-29 03:16:11.805: W/dalvikvm(454): threadid=1: thread exiting with uncaught exception (group=0x40014760)
04-29 03:16:11.825: E/AndroidRuntime(454): FATAL EXCEPTION: main
04-29 03:16:11.825: E/AndroidRuntime(454): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.Login}: java.lang.NullPointerException
04-29 03:16:11.825: E/AndroidRuntime(454): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1736)
04-29 03:16:11.825: E/AndroidRuntime(454): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1752)
04-29 03:16:11.825: E/AndroidRuntime(454): at android.app.ActivityThread.access$1500(ActivityThread.java:123)
04-29 03:16:11.825: E/AndroidRuntime(454): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:993)
04-29 03:16:11.825: E/AndroidRuntime(454): at android.os.Handler.dispatchMessage(Handler.java:99)
04-29 03:16:11.825: E/AndroidRuntime(454): at android.os.Looper.loop(Looper.java:126)
04-29 03:16:11.825: E/AndroidRuntime(454): at android.app.ActivityThread.main(ActivityThread.java:3997)
04-29 03:16:11.825: E/AndroidRuntime(454): at java.lang.reflect.Method.invokeNative(Native Method)
04-29 03:16:11.825: E/AndroidRuntime(454): at java.lang.reflect.Method.invoke(Method.java:491)
04-29 03:16:11.825: E/AndroidRuntime(454): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
04-29 03:16:11.825: E/AndroidRuntime(454): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
04-29 03:16:11.825: E/AndroidRuntime(454): at dalvik.system.NativeStart.main(Native Method)
04-29 03:16:11.825: E/AndroidRuntime(454): Caused by: java.lang.NullPointerException
04-29 03:16:11.825: E/AndroidRuntime(454): at com.example.test.Login.addListenerOnBtnlogin(Login.java:79)
04-29 03:16:11.825: E/AndroidRuntime(454): at com.example.test.Login.onCreate(Login.java:42)
04-29 03:16:11.825: E/AndroidRuntime(454): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
04-29 03:16:11.825: E/AndroidRuntime(454): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1700)
04-29 03:16:11.825: E/AndroidRuntime(454): ... 11 more
04-29 03:16:14.684: I/Process(454): Sending signal. PID: 454 SIG: 9
答案 0 :(得分：2)
我可能错了，但我认为它正在发生，因为您试图在btnLogin listener 中获取EditTexts 的值，然后才能正确引用它们来自您的XML布局文件。
首先使用 findViewById(..) 正确定义引用，然后调用侦听器。
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
getActionBar().setDisplayHomeAsUpEnabled(true);
uname = (EditText) findViewById(R.id.txtuserid);
pword = (EditText) findViewById(R.id.txtuserpass);
addListenerOnHome();
addListenerOnBtnlogin();
}