这对我来说太奇怪了！
我的应用程序在此行崩溃：
ConnectivityManager connectivity = (ConnectivityManager)_context.getSystemService(Context.CONNECTIVITY_SERVICE);
logcat显示此错误：
06-12 13:27:57.755: E/AndroidRuntime(1431): FATAL EXCEPTION: AsyncTask #1
06-12 13:27:57.755: E/AndroidRuntime(1431): java.lang.RuntimeException: An error occured while executing doInBackground()
06-12 13:27:57.755: E/AndroidRuntime(1431): at android.os.AsyncTask$3.done(AsyncTask.java:200)
06-12 13:27:57.755: E/AndroidRuntime(1431): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
06-12 13:27:57.755: E/AndroidRuntime(1431): at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
06-12 13:27:57.755: E/AndroidRuntime(1431): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
06-12 13:27:57.755: E/AndroidRuntime(1431): at java.util.concurrent.FutureTask.run(FutureTask.java:138)
06-12 13:27:57.755: E/AndroidRuntime(1431): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
06-12 13:27:57.755: E/AndroidRuntime(1431): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
06-12 13:27:57.755: E/AndroidRuntime(1431): at java.lang.Thread.run(Thread.java:1019)
06-12 13:27:57.755: E/AndroidRuntime(1431): Caused by: java.lang.NullPointerException
06-12 13:27:57.755: E/AndroidRuntime(1431): at com.example.android.helper.ConnectionDetector.isConnectingToInternet(ConnectionDetector.java:21)
06-12 13:27:57.755: E/AndroidRuntime(1431): at com.example.android.helper.JSONParser.getJSONFromUrl(JSONParser.java:53)
06-12 13:27:57.755: E/AndroidRuntime(1431): at com.example.android.Login$1.doInBackground(Login.java:220)
06-12 13:27:57.755: E/AndroidRuntime(1431): at com.example.android.Login$1.doInBackground(Login.java:1)
06-12 13:27:57.755: E/AndroidRuntime(1431): at android.os.AsyncTask$2.call(AsyncTask.java:185)
06-12 13:27:57.755: E/AndroidRuntime(1431): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
06-12 13:27:57.755: E/AndroidRuntime(1431): ... 4 more
这是我的doInBackground：
inside login.java:
public class Login extends SherlockActivity{
Activity mActivity;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
final Activity mActivity = this;
}
//and some irrelevant stuff till we get to doInBackground inside AsyncTask
protected JSONObject doInBackground(String... params) {
String phoneNo2 = params[0];
uid = phoneNo2;
publishProgress(20);
jsonParser = new JSONParser(mActivity);
List<NameValuePair> nameValuePair = new ArrayList<NameValuePair>(2);
nameValuePair.add(new BasicNameValuePair("param1", phoneNo2));
nameValuePair.add(new BasicNameValuePair("retrieve", "login"));
json = jsonParser.getJSONFromUrl(loginURL, nameValuePair);// <---- here is line number 220 inside login.java
publishProgress(40);
if(json!=null){
return json;
}
else{
MyToast mToast= new MyToast(mActivity);
mToast.showText("Connection Failed", Toast.LENGTH_SHORT);
}
return null;
}
}
现在在jsonParser类中：
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
Activity _Activity;
// flag for Internet connection status
Boolean isInternetPresent = false;
// Connection detector class
ConnectionDetector cd;
// constructor
public JSONParser(Activity act) {
this._Activity = act;
}
public JSONObject getJSONFromUrl(String url, List<NameValuePair> params) {
MyToast mToast = new MyToast(_Activity);
// creating connection detector class instance
cd = new ConnectionDetector(_Activity);
// get Internet status
isInternetPresent = cd.isConnectingToInternet();//<---- here is line number 53 inside JSONParser.java
// check for Internet status
if (isInternetPresent) {
mToast.showText("Connection Present", Toast.LENGTH_SHORT);
// Making HTTP request
try {
HttpParams httpParameters = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(httpParameters, 4000);
HttpConnectionParams.setSoTimeout(httpParameters, 6000);
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (ConnectTimeoutException e) {
mToast.showText("connection failed", Toast.LENGTH_LONG);
}catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "n");
}
is.close();
json = sb.toString();
Log.e("JSON", json);
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
return jObj;
} else {
mToast.showText("please check you internet connection", Toast.LENGTH_SHORT);
}
// return JSON String
return null;
}
}
现在在ConnectionDetector类中：
public class ConnectionDetector {
private Context _context;
public ConnectionDetector(Context context){
this._context = context;
}
public boolean isConnectingToInternet(){
//here is exactly where the app crashes: line number 21 inside ConnectionDetector.java
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;
}
}
它完全崩溃在这一行：
ConnectivityManager connectivity = (ConnectivityManager)_context.getSystemService(Context.CONNECTIVITY_SERVICE);
这是在AndroidManifest.xml中：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="5"
android:targetSdkVersion="19" />
<uses-permission android:name="android.permission.READ_CONTACTS"/>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<application
android:allowBackup="false"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/Theme.Avatheme"
android:uiOptions="splitActionBarWhenNarrow" android:supportsRtl="true">
<!-- Splash screen -->
<activity
android:name="com.example.android.SplashScreen"
android:screenOrientation="portrait"
android:theme="@android:style/Theme.Black.NoTitleBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!-- Main activity -->
<activity
android:name="com.example.android.MainActivity"
android:label="@string/app_name" >
</activity>
<activity android:name="com.example.android.Login"></activity>
</application>
</manifest>