我正在观看关于Android与远程数据库的连接的教程，但不知何故它崩溃了，我不明白为什么。我包括代码请看看，告诉我是否可以解决它。
package com.example.mysqltest;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class Login extends Activity implements OnClickListener {
private EditText user, pass;
private Button mSubmit, mRegister;
TextView tv;
// Progress Dialog
private ProgressDialog pDialog;
// JSON parser class
JSONParser jsonParser = new JSONParser();
// php login script location:
// localhost :
// testing on your device
// put your local ip instead, on windows, run CMD > ipconfig
// or in mac's terminal type ifconfig and look for the ip under en0 or en1
// private static final String LOGIN_URL =
// "http://xxx.xxx.x.x:1234/webservice/login.php";
// testing on Emulator:
private static final String LOGIN_URL = "http://localhost:8080/webservice/login.php";
// testing from a real server:
// private static final String LOGIN_URL =
// "http://www.mybringback.com/webservice/login.php";
// JSON element ids from repsonse of php script:
private static final String TAG_SUCCESS = "success";
private static final String TAG_MESSAGE = "message";
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
tv = (TextView) findViewById(R.id.textView2);
// setup input fields
user = (EditText) findViewById(R.id.username);
pass = (EditText) findViewById(R.id.password);
// setup buttons
mSubmit = (Button) findViewById(R.id.login);
mRegister = (Button) findViewById(R.id.register);
// register listeners
mSubmit.setOnClickListener(this);
mRegister.setOnClickListener(this);
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
switch (v.getId()) {
case R.id.login:
new AttemptLogin().execute();
break;
case R.id.register:
Intent i = new Intent(this, Register.class);
startActivity(i);
break;
default:
break;
}
}
class AttemptLogin extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(Login.this);
pDialog.setMessage("Attempting login...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected String doInBackground(String... args) {
// TODO Auto-generated method stub
// Check for success tag
int success;
String username = user.getText().toString();
String password = pass.getText().toString();
try {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("username", username));
params.add(new BasicNameValuePair("password", password));
Log.d("request!", "starting");
// getting product details by making HTTP request
JSONObject json = jsonParser.makeHttpRequest(LOGIN_URL, "POST",
params);
// check your log for json response
Log.d("Login attempt", json.toString());
// json success tag
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
tv.setText("Success");
// Log.d("Login Successful!", json.toString());
// // save user data
// SharedPreferences sp = PreferenceManager
// .getDefaultSharedPreferences(Login.this);
// Editor edit = sp.edit();
// edit.putString("username", username);
// edit.commit();
//
// Intent i = new Intent(Login.this, ReadComments.class);
// finish();
// startActivity(i);
// return json.getString(TAG_MESSAGE);
} else {
// Log.d("Login Failure!", json.getString(TAG_MESSAGE));
// return json.getString(TAG_MESSAGE);
tv.setText("Failed");
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String file_url) {
// dismiss the dialog once product deleted
pDialog.dismiss();
if (file_url != null) {
Toast.makeText(Login.this, file_url, Toast.LENGTH_LONG).show();
}
}
}
}
如果您需要查看LogCat，日志信息就在这里
07-16 05:05:48.274: E/Buffer Error(313): Error converting result java.lang.NullPointerException
07-16 05:05:48.274: E/JSON Parser(313): Error parsing data org.json.JSONException: End of input at character 0 of
07-16 05:05:48.274: W/dalvikvm(313): threadid=9: thread exiting with uncaught exception (group=0x40015560)
07-16 05:05:48.284: E/AndroidRuntime(313): FATAL EXCEPTION: AsyncTask #1
07-16 05:05:48.284: E/AndroidRuntime(313): java.lang.RuntimeException: An error occured while executing doInBackground()
07-16 05:05:48.284: E/AndroidRuntime(313): at android.os.AsyncTask$3.done(AsyncTask.java:200)
07-16 05:05:48.284: E/AndroidRuntime(313): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
07-16 05:05:48.284: E/AndroidRuntime(313): at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
07-16 05:05:48.284: E/AndroidRuntime(313): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
07-16 05:05:48.284: E/AndroidRuntime(313): at java.util.concurrent.FutureTask.run(FutureTask.java:138)
07-16 05:05:48.284: E/AndroidRuntime(313): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
07-16 05:05:48.284: E/AndroidRuntime(313): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
07-16 05:05:48.284: E/AndroidRuntime(313): at java.lang.Thread.run(Thread.java:1019)
07-16 05:05:48.284: E/AndroidRuntime(313): Caused by: java.lang.NullPointerException
07-16 05:05:48.284: E/AndroidRuntime(313): at com.example.mysqltest.Login$AttemptLogin.doInBackground(Login.java:125)
07-16 05:05:48.284: E/AndroidRuntime(313): at com.example.mysqltest.Login$AttemptLogin.doInBackground(Login.java:1)
07-16 05:05:48.284: E/AndroidRuntime(313): at android.os.AsyncTask$2.call(AsyncTask.java:185)
07-16 05:05:48.284: E/AndroidRuntime(313): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
07-16 05:05:48.284: E/AndroidRuntime(313): ... 4 more
07-16 05:05:48.294: W/ActivityManager(61): Force finishing activity com.example.mysqltest/.Login
07-16 05:05:48.434: W/IInputConnectionWrapper(313): showStatusIcon on inactive InputConnection
07-16 05:05:48.964: E/WindowManager(313): Activity com.example.mysqltest.Login has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@40564ea8 that was originally added here
07-16 05:05:48.964: E/WindowManager(313): android.view.WindowLeaked: Activity com.example.mysqltest.Login has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@40564ea8 that was originally added here
07-16 05:05:48.964: E/WindowManager(313): at android.view.ViewRoot.<init>(ViewRoot.java:258)
07-16 05:05:48.964: E/WindowManager(313): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
07-16 05:05:48.964: E/WindowManager(313): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
07-16 05:05:48.964: E/WindowManager(313): at android.view.Window$LocalWindowManager.addView(Window.java:424)
07-16 05:05:48.964: E/WindowManager(313): at android.app.Dialog.show(Dialog.java:241)
07-16 05:05:48.964: E/WindowManager(313): at com.example.mysqltest.Login$AttemptLogin.onPreExecute(Login.java:103)
07-16 05:05:48.964: E/WindowManager(313): at android.os.AsyncTask.execute(AsyncTask.java:391)
07-16 05:05:48.964: E/WindowManager(313): at com.example.mysqltest.Login.onClick(Login.java:82)
07-16 05:05:48.964: E/WindowManager(313): at android.view.View.performClick(View.java:2485)
07-16 05:05:48.964: E/WindowManager(313): at android.view.View$PerformClick.run(View.java:9080)
07-16 05:05:48.964: E/WindowManager(313): at android.os.Handler.handleCallback(Handler.java:587)
07-16 05:05:48.964: E/WindowManager(313): at android.os.Handler.dispatchMessage(Handler.java:92)
07-16 05:05:48.964: E/WindowManager(313): at android.os.Looper.loop(Looper.java:123)
07-16 05:05:48.964: E/WindowManager(313): at android.app.ActivityThread.main(ActivityThread.java:3683)
07-16 05:05:48.964: E/WindowManager(313): at java.lang.reflect.Method.invokeNative(Native Method)
07-16 05:05:48.964: E/WindowManager(313): at java.lang.reflect.Method.invoke(Method.java:507)
07-16 05:05:48.964: E/WindowManager(313): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
07-16 05:05:48.964: E/WindowManager(313): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
07-16 05:05:48.964: E/WindowManager(313): at dalvik.system.NativeStart.main(Native Method)
07-16 05:05:54.016: D/dalvikvm(313): GC_EXPLICIT freed 118K, 53% free 2662K/5639K, external 551K/961K, paused 105ms
07-16 05:05:54.376: D/SntpClient(61): request time failed: java.net.SocketException: Address family not supported by protocol
07-16 05:05:56.704: I/Process(313): Sending signal. PID: 313 SIG: 9
07-16 05:05:56.754: W/InputManagerService(61): Window already focused, ignoring focus gain of: com.android.internal.view.IInputMethodClient$Stub$Proxy@407536a8
07-16 05:05:56.854: I/ActivityManager(61): Process com.example.mysqltest (pid 313) has died.
07-16 05:08:00.014: I/dalvikvm(61): Jit: resizing JitTable from 1024 to 2048
07-16 05:10:00.135: D/dalvikvm(129): GC_CONCURRENT freed 223K, 51% free 2813K/5703K, external 544K/1021K, paused 9ms+4ms
07-16 05:10:54.386: D/SntpClient(61): request time failed: java.net.SocketException: Address family not supported by protocol
07-16 05:11:00.125: D/dalvikvm(61): GC_CONCURRENT freed 673K, 44% free 4282K/7623K, external 1226K/2327K, paused 5ms+6ms
07-16 05:15:54.396: D/SntpClient(61): request time failed: java.net.SocketException: Address family not supported by protocol
07-16 05:20:54.404: D/SntpClient(61): request time failed: java.net.SocketException: Address family not supported by protocol.
根据LogCat的主要问题在于doInBackground方法。
以下是完整源代码的下载链接。 http://dchabmztumu0g.cloudfront.net/wp-content/uploads/2013/05/remote-sql-android-6.zip 感谢任何帮助。
答案 0 :(得分：0)
我认为logcat告诉你这是什么问题
Error converting result java.lang.NullPointerException
以及
Error parsing data org.json.JSONException: End of input at character 0 of
你正在从后台线程操纵UI，所以它引发了一个错误，另一个是你从doinbackground返回null然后使用该null作为file_url
并且JSONException告诉您字符串结果为空
答案 1 :(得分：0)
通过执行以下检查确保您的json不为空 -
@Override
protected String doInBackground(String... args) {
// TODO Auto-generated method stub
// Check for success tag
int success;
String username = user.getText().toString();
String password = pass.getText().toString();
try {
// Building Parameters
List<NameValuePair> params = new
ArrayList<NameValuePair>();
params.add(new
BasicNameValuePair("username", username));
params.add(new
BasicNameValuePair("password", password));
Log.d("request!", "starting");
// getting product details by making HTTP request
JSONObject json = jsonParser.
makeHttpRequest(LOGIN_URL, "POST",
params);
if(json != null && !json.isNull(TAG_SUCCESS)){
// check your log for json response
Log.d("Login attempt", json.toString());
// json success tag
success = json.getInt(TAG_SUCCESS);
}
else
{
Log.d("Login attempt", "Null Json");
success = 0;
}
return success + "";
}
protected void onPostExecute(String success) {
// dismiss the dialog once product deleted
pDialog.dismiss();
if(success.equals("1"))
tv.setText("Success");
else
tv.setText("Failed");
}
}
另请注意，您无法从后台线程更新UI的内容。您可以将结果传递给可以更新UI的onPostExecute，如上面的代码中所述。