我正在尝试创建一个需要连接到本地服务器以提取数据的应用程序！ 当有连接时，应用程序工作正常！但是当连接断开时，应用程序会等待大约15秒然后崩溃！我在互联网上看到了所有可能的解决方案但没有人为我工作！ 请一手解决这个问题 这是源代码！
package com.example.chap6_5;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.channels.UnresolvedAddressException;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.conn.ConnectTimeoutException;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONObject;
import android.app.Activity;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
EditText Username, Password;
TextView Error_Login;
Button Button_Login;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Username = (EditText) findViewById(R.id.username);
Password = (EditText) findViewById(R.id.password);
Error_Login = (TextView)findViewById(R.id.ErrorLogin);
Button_Login = (Button)findViewById(R.id.login);
Button_Login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
new DownloadTextTask().execute("http://192.168.1.100/PHP_MVC/mobile/MLogin.php");
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
// ---Connects using HTTP POST---
public InputStream OpenHttpPOSTConnection(String url) {
InputStream inputStream = null;
try {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
// ---the key/value pairs to post to the server---
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
nameValuePairs.add(new BasicNameValuePair("username", Username.getText().toString()
.toString()));
nameValuePairs.add(new BasicNameValuePair("password", Password.getText().toString()));
httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse httpResponse = httpclient.execute(httpPost);
inputStream = httpResponse.getEntity().getContent();
}
catch (ConnectTimeoutException e)
{
Log.d("OpenHttpPOSTConnection TIMEOUT", e.getLocalizedMessage());
}
catch (Exception e) {
Log.d("OpenHttpPOSTConnection", e.getLocalizedMessage());
}
return inputStream;
}
private String DownloadText(String URL) {
int BUFFER_SIZE = 2000;
InputStream in = null;
try {
in = OpenHttpPOSTConnection(URL);
}
catch (Exception e) {
Log.d("Networking", e.getLocalizedMessage());
return "";
}
InputStreamReader isr = new InputStreamReader(in);
int charRead;
String str = "";
char[] inputBuffer = new char[BUFFER_SIZE];
try {
while ((charRead = isr.read(inputBuffer)) > 0) {
// ---convert the chars to a String---
String readString = String
.copyValueOf(inputBuffer, 0, charRead);
str += readString;
inputBuffer = new char[BUFFER_SIZE];
}
in.close();
} catch (IOException e) {
Log.d("DownloadText", e.getLocalizedMessage());
return "";
}
return str;
}
private class DownloadTextTask extends AsyncTask<String, Void, String> {
protected String doInBackground(String... urls) {
return DownloadText(urls[0]);
}
@Override
protected void onPostExecute(String result) {
try {
JSONObject jsonObject = new JSONObject(result);
String success = jsonObject.getString("Success");
Toast.makeText(getBaseContext(), success, Toast.LENGTH_LONG).show();
if (Integer.parseInt(success)==1)
{
Log.d("DownloadTextTask", "success");
Intent i_Dashboard = new Intent(getApplicationContext(),Dashboard.class);
startActivity(i_Dashboard);
finish();
}
else
{
Error_Login.setText("Error Login : Username/password are wrong !");
}
Log.d("DownloadTextTask", result);
} catch (Exception e) {
Log.d("DownloadText", e.getLocalizedMessage());
}
}
}
}
[EDITED]新的OnCreate方法
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Username = (EditText) findViewById(R.id.username);
Password = (EditText) findViewById(R.id.password);
Error_Login = (TextView)findViewById(R.id.ErrorLogin);
Button_Login = (Button)findViewById(R.id.login);
Button_Login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
ConnectionDetector conn = new ConnectionDetector(getApplicationContext());
if(conn.isConnectingToInternet())
{
Toast.makeText(getApplicationContext(), "CONNECTEDs", Toast.LENGTH_LONG).show();
new DownloadTextTask().execute("http://192.168.1.100/PHP_MVC/mobile/MLogin.php");
}
else
Toast.makeText(getApplicationContext(), "No connection", Toast.LENGTH_LONG).show();
}
});
}
这是logcat：
05-01 06:08:07.673: D/OpenGLRenderer(1276): TextureCache::get: create texture(0xb881bb38): name, size, mSize = 13, 7488, 1106852
05-01 06:08:10.773: D/OpenHttpPOSTConnection TIMEOUT(1276): Connect to /192.168.1.100:80 timed out
05-01 06:08:10.773: W/dalvikvm(1276): threadid=10: thread exiting with uncaught exception (group=0xa62b0288)
05-01 06:08:10.773: E/AndroidRuntime(1276): FATAL EXCEPTION: AsyncTask #1
05-01 06:08:10.773: E/AndroidRuntime(1276): java.lang.RuntimeException: An error occured while executing doInBackground()
05-01 06:08:10.773: E/AndroidRuntime(1276): at android.os.AsyncTask$3.done(AsyncTask.java:299)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
05-01 06:08:10.773: E/AndroidRuntime(1276): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.lang.Thread.run(Thread.java:856)
05-01 06:08:10.773: E/AndroidRuntime(1276): Caused by: java.lang.NullPointerException
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.io.Reader.<init>(Reader.java:64)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.io.InputStreamReader.<init>(InputStreamReader.java:122)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.io.InputStreamReader.<init>(InputStreamReader.java:59)
05-01 06:08:10.773: E/AndroidRuntime(1276): at com.example.chap6_5.MainActivity.DownloadText(MainActivity.java:118)
05-01 06:08:10.773: E/AndroidRuntime(1276): at com.example.chap6_5.MainActivity.access$0(MainActivity.java:106)
05-01 06:08:10.773: E/AndroidRuntime(1276): at com.example.chap6_5.MainActivity$DownloadTextTask.doInBackground(MainActivity.java:140)
05-01 06:08:10.773: E/AndroidRuntime(1276): at com.example.chap6_5.MainActivity$DownloadTextTask.doInBackground(MainActivity.java:1)
05-01 06:08:10.773: E/AndroidRuntime(1276): at android.os.AsyncTask$2.call(AsyncTask.java:287)
05-01 06:08:10.773: E/AndroidRuntime(1276): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
05-01 06:08:10.773: E/AndroidRuntime(1276): ... 5 more
05-01 06:08:10.893: D/OpenGLRenderer(1276): TextureCache::get: create texture(0xb87ab998): name, size, mSize = 24, 7488, 1114340
05-01 06:08:11.329: D/OpenGLRenderer(1276): TextureCache::flush: target size: 668604
05-01 06:08:11.329: D/OpenGLRenderer(1276): TextureCache::callback: name, removed size, mSize = 2, 5184, 1109156
05-01 06:08:11.329: D/OpenGLRenderer(1276): TextureCache::callback: name, removed size, mSize = 4, 20736, 1088420
05-01 06:08:11.329: D/OpenGLRenderer(1276): TextureCache::callback: name, removed size, mSize = 10, 2304, 1086116
05-01 06:08:11.329: D/OpenGLRenderer(1276): TextureCache::callback: name, removed size, mSize = 13, 7488, 1078628
05-01 06:08:11.329: D/OpenGLRenderer(1276): TextureCache::callback: name, removed size, mSize = 6, 7488, 1071140
05-01 06:08:11.329: D/OpenGLRenderer(1276): TextureCache::callback: name, removed size, mSize = 1, 1048576, 22564
非常感谢！
答案 0 :(得分：2)
第一种方法
在OpenHttpPOSTConnection功能中，检查互联网状态
...
HttpResponse httpResponse = httpclient.execute(httpPost);
if(httpResponse.getStatusLine().getStatusCode() == 200) //which means there is connection
inputStream = httpResponse.getEntity().getContent();
else
return null;
然后检查null是否离开AsyncTask ..通过提供onPostExcute和null值，并依赖null显示toast告诉用户没有Internet连接。
第二种方法
您也可以拥有一个ConnectionDetector类，在执行AsyncTask之前检查是否存在Internet连接。
public class ConnectionDetector {
private Context _context;
public ConnectionDetector(Context context){
this._context = context;
}
public boolean isConnectingToInternet(){
ConnectivityManager connectivity = (ConnectivityManager) _context.getSystemService(Context.CONNECTIVITY_SERVICE);
if (connectivity != null)
{
NetworkInfo[] info = connectivity.getAllNetworkInfo();
if (info != null)
for (int i = 0; i < info.length; i++)
if (info[i].getState() == NetworkInfo.State.CONNECTED)
{
return true;
}
}
return false;
}
}
然后在执行AysncTask：
ConnectionDetector conn = new ConnectionDetector(getApplicationContext());
if(conn.isConnectiontoInternet())
new DownloadTextTask().execute("http://192.168.1.100/PHP_MVC/mobile/MLogin.php");
else
//show toast.
P.S：请务必将此权限添加到您的清单中：
<!-- Network State Permissions -->
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
答案 1 :(得分：1)
你得到一个空指针异常。检查空值，然后如果得到空值，则相应地执行逻辑。最重要的是，您应该在执行网络IO之前检查是否有网络连接，以帮助防止发生这些类型的问题。
您可以按照此问题中列出的解决方案执行此操作：Detect whether there is an Internet connection available on Android
答案 2 :(得分：0)
如果InputStream in = null，则会发生这种情况。如果网络关闭，OpenHttpPOSTConnection将尝试从网络读取并将失败并抛出异常。你抓住这个。这将导致函数返回null，并且inputstream将为null。
对OpenHttpPOSTConnection的返回值进行空检查将解决此问题