我需要帮助才能找到有关我的Android应用的解决方案。尝试登录应用程序后，我收到以下错误。应用程序停止运行（强制停止）。 Fyi，我是开发Android应用程序的新手。
09-15 00:31:42.602: E/AndroidRuntime(2755): FATAL EXCEPTION: main
09-15 00:31:42.602: E/AndroidRuntime(2755): Process: com.mobile.learning, PID: 2755
09-15 00:31:42.602: E/AndroidRuntime(2755): java.lang.NullPointerException: println needs a message
09-15 00:31:42.602: E/AndroidRuntime(2755): at android.util.Log.println_native(Native Method)
09-15 00:31:42.602: E/AndroidRuntime(2755): at android.util.Log.d(Log.java:139)
09-15 00:31:42.602: E/AndroidRuntime(2755): at com.mobile.learning.login$1.onClick(login.java:61)
09-15 00:31:42.602: E/AndroidRuntime(2755): at android.view.View.performClick(View.java:4756)
09-15 00:31:42.602: E/AndroidRuntime(2755): at android.view.View$PerformClick.run(View.java:19749)
09-15 00:31:42.602: E/AndroidRuntime(2755): at android.os.Handler.handleCallback(Handler.java:739)
09-15 00:31:42.602: E/AndroidRuntime(2755): at android.os.Handler.dispatchMessage(Handler.java:95)
09-15 00:31:42.602: E/AndroidRuntime(2755): at android.os.Looper.loop(Looper.java:135)
09-15 00:31:42.602: E/AndroidRuntime(2755): at android.app.ActivityThread.main(ActivityThread.java:5221)
09-15 00:31:42.602: E/AndroidRuntime(2755): at java.lang.reflect.Method.invoke(Native Method)
09-15 00:31:42.602: E/AndroidRuntime(2755): at java.lang.reflect.Method.invoke(Method.java:372)
09-15 00:31:42.602: E/AndroidRuntime(2755): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
09-15 00:31:42.602: E/AndroidRuntime(2755): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
这是我的login.java：
package com.mobile.learning;
import mobile.config.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.os.StrictMode;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class login extends Activity {
public koneksi linkurl;
String SERVER_URL;
private Button login;
private EditText username, password;
public ProgressDialog progressDialog;
//private TextView notif;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.signin);
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
login = (Button) findViewById(R.id.login);
username = (EditText) findViewById(R.id.uname);
password = (EditText) findViewById(R.id.passwd);
//final TextView notif = (TextView) findViewById(R.id.tv_error);
login.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
String Re;
String mUsername = username.getText().toString();
String mPassword = password.getText().toString();
Re=tryLogin(mUsername, mPassword);
Log.d("Check","Here");
Log.d("Re",Re);
String temp_check=Re.trim();
if(temp_check.equals("1"))
{
String nama = username.getText().toString();
Intent newIntent = new Intent(login.this, halamanUtama.class);
String txtnama = String.valueOf(nama);
//membuat Bundle
Bundle bundle = new Bundle();
//menentukan parameter Bundle (id,isi) --> id=nama dan isinya adalah variabel dari txtnama
bundle.putString("nama", txtnama);
//menambahkan bundle pada intent
newIntent.putExtras(bundle);
startActivityForResult(newIntent, 0);
//notif.setText("SUKSES");
}
else
{
createDialog("Maaf", "Username Atau Password Salah !");
}
}
});
}
protected String tryLogin(String mUsername, String mPassword)
{
Log.d(" TryLoginCheck ","Here");
HttpURLConnection connection;
OutputStreamWriter request = null;
URL url = null;
String response = null;
String temp=null;
String parameters = "username="+mUsername+"&password="+mPassword;
System.out.println("UserName"+mUsername+"\n"+"password"+mPassword);
Log.d("Parameters",parameters);
try
{
;
linkurl = new koneksi("/login.php");
SERVER_URL = linkurl.getUrl();
//"http://182.6.232.37:80/ta/login.php"
url = new URL(SERVER_URL);
connection = (HttpURLConnection) url.openConnection();
connection.setDoOutput(true);
connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
connection.setRequestMethod("POST");
request = new OutputStreamWriter(connection.getOutputStream());
request.write(parameters);
request.flush();
request.close();
String line = "";
InputStreamReader isr = new InputStreamReader(connection.getInputStream());
BufferedReader reader = new BufferedReader(isr);
StringBuilder sb = new StringBuilder();
while ((line = reader.readLine()) != null)
{
sb.append(line + "\n");
}
temp=sb.toString();
Log.d("Temp",temp);
// Response from server after login process will be stored in response variable.
response = sb.toString();
Log.d("Response",response);
Log.d("Sb Value",sb.toString());
isr.close();
reader.close();
}
catch(IOException e)
{
Toast.makeText(this,e.toString(),0).show();
}
// Log.d("Response",response);
return response;
}
private void createDialog(String title, String text) {
AlertDialog ad = new AlertDialog.Builder(this)
.setPositiveButton("Ok", null)
.setTitle(title)
.setMessage(text)
.create();
ad.show();
}
}
答案 0 :(得分：1)
此代码导致的错误：Log.d（“Re”，Re）; ，我认为由tryLogin函数引起的错误/异常导致Re == null。也许你需要在tryLogin中检查你的代码。或最简单的解决方案改变：
String response = null;
String temp=null;
带
String response = ""; //or anything string in here
String temp=null;
答案 1 :(得分：0)
看起来Re为空。如果你在tryLogin（）中得到异常，就会发生这种情况。
这就是Log.d("Re",Re);引发这种情况的方式。
为什么你试试Log.d("Re",null);
检查Re是否为null bevore如果在tryLogin（）中出现异常，则记录或返回空字符串。