我在运行RssReader的Android项目时出错。
代码:
URL url = new URL(urlToRssFeed);
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();
XMLReader xmlreader = parser.getXMLReader();
RssHandler theRSSHandler = new RssHandler();
xmlreader.setContentHandler(theRSSHandler);
InputSource is = new InputSource(url.openStream());
xmlreader.parse(is);
return theRSSHandler.getFeed();
它显示以下错误:
android.os.NetworkOnMainThreadException
如何解决此问题?
该错误是由于在主线程中执行长时间运行的操作造成的。您可以使用AsynTask或thread轻松纠正该问题。您可以签出此库AsyncHTTPClient以获得更好的处理。
AsyncHttpClient client = new AsyncHttpClient();
client.get("http://www.google.com", new AsyncHttpResponseHandler() {
@Override
public void onStart() {
// Called before a request is started
}
@Override
public void onSuccess(int statusCode, Header[] headers, byte[] response) {
// Called when response HTTP status is "200 OK"
}
@Override
public void onFailure(int statusCode, Header[] headers, byte[] errorResponse, Throwable e) {
// Called when response HTTP status is "4XX" (for example, 401, 403, 404)
}
@Override
public void onRetry(int retryNo) {
// Called when request is retried
}
});
已经介绍了新的线程和异步任务解决方案。
AsyncTask理想情况下应用于短操作。普通线程不适用于Android。
看看使用HandlerThread和Handler的替代解决方案
处理程序线程
用于启动带有弯针的新线程的便捷类。然后可以使用looper创建处理程序类。请注意,仍然必须调用start()。
处理程序:
处理程序允许您发送和处理与线程的MessageQueue关联的Message和Runnable对象。每个Handler实例都与一个线程和该线程的消息队列相关联。当您创建一个新的处理程序时,它被绑定到正在创建它的线程的线程/消息队列——从那时起,它将向该消息队列传递消息和可运行文件,并在它们从消息队列中出来时执行它们。
解决方案:
创建HandlerThread在HandlerThread上调用start()通过从HanlerThread获取Looper创建处理程序在Runnable对象中嵌入与网络操作相关的代码将可运行任务提交给处理程序
示例代码段,用于处理NetworkOnMainThreadException
HandlerThread handlerThread = new HandlerThread("URLConnection");
handlerThread.start();
handler mainHandler = new Handler(handlerThread.getLooper());
Runnable myRunnable = new Runnable() {
@Override
public void run() {
try {
Log.d("Ravi", "Before IO call");
URL page = new URL("http://www.google.com");
StringBuffer text = new StringBuffer();
HttpURLConnection conn = (HttpURLConnection) page.openConnection();
conn.connect();
InputStreamReader in = new InputStreamReader((InputStream) conn.getContent());
BufferedReader buff = new BufferedReader(in);
String line;
while ( (line = buff.readLine()) != null) {
text.append(line + "\n");
}
Log.d("Ravi", "After IO call");
Log.d("Ravi",text.toString());
}catch( Exception err){
err.printStackTrace();
}
}
};
mainHandler.post(myRunnable);
使用此方法的优点:
为每个网络操作创建新的线程/异步任务非常昂贵。线程/异步任务将被销毁并重新创建,以用于下一次网络操作。但使用Handler和HandlerThread方法,您可以通过使用Handler将许多网络操作(作为可运行任务)提交给单个HandlerThread。
在活动中使用此项
btnsub.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
new Thread(new Runnable() {
@Override
public void run() {
// TODO Auto-generated method stub
//Initialize soap request + add parameters
SoapObject request = new SoapObject(NAMESPACE, METHOD_NAME1);
//Use this to add parameters
request.addProperty("pincode", txtpincode.getText().toString());
request.addProperty("bg", bloodgroup.getSelectedItem().toString());
//Declare the version of the SOAP request
SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);
envelope.setOutputSoapObject(request);
envelope.dotNet = true;
try {
HttpTransportSE androidHttpTransport = new HttpTransportSE(URL);
//this is the actual part that will call the webservice
androidHttpTransport.call(SOAP_ACTION1, envelope);
// Get the SoapResult from the envelope body.
SoapObject result = (SoapObject) envelope.getResponse();
Log.e("result data", "data" + result);
SoapObject root = (SoapObject) result.getProperty(0);
// SoapObject s_deals = (SoapObject) root.getProperty(0);
// SoapObject s_deals_1 = (SoapObject) s_deals.getProperty(0);
//
System.out.println("********Count : " + root.getPropertyCount());
value = new ArrayList<Detailinfo>();
for (int i = 0; i < root.getPropertyCount(); i++) {
SoapObject s_deals = (SoapObject) root.getProperty(i);
Detailinfo info = new Detailinfo();
info.setFirstName(s_deals.getProperty("Firstname").toString());
info.setLastName(s_deals.getProperty("Lastname").toString());
info.setDOB(s_deals.getProperty("DOB").toString());
info.setGender(s_deals.getProperty("Gender").toString());
info.setAddress(s_deals.getProperty("Address").toString());
info.setCity(s_deals.getProperty("City").toString());
info.setState(s_deals.getProperty("State").toString());
info.setPinecode(s_deals.getProperty("Pinecode").toString());
info.setMobile(s_deals.getProperty("Mobile").toString());
info.setEmail(s_deals.getProperty("Email").toString());
info.setBloodgroup(s_deals.getProperty("Bloodgroup").toString());
info.setAdddate(s_deals.getProperty("Adddate").toString());
info.setWaight(s_deals.getProperty("waight").toString());
value.add(info);
}
} catch (Exception e) {
e.printStackTrace();
}
Intent intent = new Intent(getApplicationContext(), ComposeMail.class);
//intent.putParcelableArrayListExtra("valuesList", value);
startActivity(intent);
}
}).start();
}
});
永远不要在UI线程上执行任何长时间运行的工作。长时间运行的工作可以是与服务器通信、读取/写入文件等。这些任务应该在后台线程上。这就是创建服务、异步任务和线程的原因。您可以禁用StrictMode,这将防止崩溃。但是,这是绝对不建议的。
我建议您至少在调试模式下利用StrictMode。使用下面的代码获取主线程上减慢应用程序速度的任何问题的日志。
StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
.detectAll()
.penaltyLog()
.build());
您可以设置不同的惩罚:
penaltyLog() // to print log
penaltyDeath() // This will crash you App(so costly penalty)
penaltyDialog() // Show alert when something went lazy on Main thread
这里有更多关于StrictMode的信息:StrictMode|Android开发者。