Android - android.os.NetworkOnMainThreadException

问题

I have this exception and I was reading a thread on this, and it seemed confusing:

How to fix android.os.NetworkOnMainThreadException?

I already added this line to my manifest:

<uses-permission android:name=\"android.permission.INTERNET\" />

On that discussion, they talk about the main execution thread of the app not being able to do networking. What I am wondering is how to restructure my code so that it is inline with Android good practices.

Here is my Activity class for this:

package com.problemio;

import java.io.InputStream;
import java.util.ArrayList;

import org.apache.http.HttpEntity;
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.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class LoginActivity extends Activity 
{
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        // Show form for login_email
        final EditText loginEmail = (EditText) findViewById(R.id.login_email);  
        String name = loginEmail.getText().toString();  

        // Show field for password  
        final EditText password = (EditText) findViewById(R.id.password);  
        String text = password.getText().toString();                  

        // Show button for submit
        Button submit = (Button)findViewById(R.id.submit);   




        // Show options for create-profile and forgot-password




        submit.setOnClickListener(new Button.OnClickListener() 
        {  
           public void onClick(View v) 
           {
              String email = loginEmail.getText().toString();
              String pass = password.getText().toString(); 
              sendFeedback(pass, email);
            }
        });        
    }


    public void sendFeedback(String pass , String email) 
    {  
        Log.d( \"1\" , pass );
        Log.d( \"1\" , email );

        // Go to db and check if these r legit
        // How do I do that? :)
        ArrayList<NameValuePair> postParameters = new ArrayList<NameValuePair>();  
        postParameters.add(new BasicNameValuePair(\"username\", email ));  
        postParameters.add(new BasicNameValuePair(\"password\", pass ));

        String responseString = null;

        try 
        {  
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost(\"myUrl\");

            // no idea what this does :)
            httppost.setEntity(new UrlEncodedFormEntity(postParameters));

            // This is the line that send the request
            HttpResponse response = httpclient.execute(httppost);

            HttpEntity entity = response.getEntity();            

            InputStream is = entity.getContent();
        } 
        catch (Exception e) 
        {     
            Log.e(\"log_tag\", \"Error in http connection \"+e.toString());
        }        
    }          
}

What am I doing wrong here and how could I fix it? :) Thanks!!

回答1:

NetworkOnMainThreadException: The exception that is thrown when an application attempts to perform a networking operation on its main thread.

You should call sendfeedback method on asynctask then only above code will work. As webserver is taking lot of time to response main thread becomes unresponsive. To avoid it you should call it on another thread. Hence asynctask is better.

here is link that illustrates how to use asynctask

回答2:

NetworkOnMainThreadException is thrown when your app tries networking operation in main thread.

To fix that you can use a private inner class within your Activity that extends android.os.AsyncTask<Params, Progress, Result> which will do the server call stuffs.

Something as,

private class SendfeedbackJob extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String[] params) {
        // do above Server call here
        return "some message";
    }

    @Override
    protected void onPostExecute(String message) {
        //process message
    }
}

And then invoke above class from submit.setOnClickListener as below,

SendfeedbackJob job = new SendfeedbackJob();
job.execute(pass, email);

References

AsyncTask doc

AsyncTask Android example

回答3:

if (android.os.Build.VERSION.SDK_INT > 9) {
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);
}

回答4:

 try 
    {  
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost("myUrl");

        // no idea what this does :)
        httppost.setEntity(new UrlEncodedFormEntity(postParameters));

        // This is the line that send the request
        HttpResponse response = httpclient.execute(httppost);

        HttpEntity entity = response.getEntity();            

        InputStream is = entity.getContent();
    } 
    catch (Exception e) 
    {     
        Log.e("log_tag", "Error in http connection "+e.toString());
    }

Here is your problem. Since api 11, this exception will inform you that you are running long tasks on the ui thread (the http communication in your class), and according with the new StrictGuard policy this is not possibile. So you have two different choice

Use thread or aynctask in order to execut yout long term task (better way)

回答5:

You made network call on main thread which is against to android rules, so you have to do your network call on separate thread like asynctask or handler etc.

回答6:

You can just create Async class as below

class Retrievedata extends AsyncTask<String, Void, String> {
@Override
    protected String doInBackground(String... params) {
         try{
                //Your code 
                }
        return null;
    }
}

You can just put your all code inside doInBackground method

回答7:

look at this link : https://developer.android.com/reference/android/os/NetworkOnMainThreadException.html

The exception that is thrown when an application attempts to perform a networking operation on its main thread. Applications targeting earlier SDK versions are allowed to do networking on their main event loop threads, but it's heavily discouraged.

if you set minSdkVersion <11, then your application will work and you can run network operation in main thread.

回答8:

Main thread is the UI thread and you cannot do a operation in the main thread which may block the user Interaction.So to avoid this create a simple handler and update main thread if you want.

Runnable runnable;
Handler newHandler;

newHandler = new Handler();
runnable = new Runnable() {
    @Override
    public void run() {
        try {
            //update UI
        } catch (Exception e) {
            e.printStackTrace();
        } 
    }
};
runnable.run();

to stop the thread use

newHandler.removeCallbacks(runnable);

For more info check this out. https://android-developers.googleblog.com/2009/05/painless-threading.html

回答9:

After a long research (lasted half day) I have found a solution for my problem which is similar to the problem indicated here. The exception displayed by my Android Studio 2.3.3 was this:

android studio android.os.networkonmainthreadexception

The problem was based on the impossibility to set a UI variable in the MainActivity. So I saw the following video and I solved my problem. I hope it is also useful to others:

How to avoid android os NetworkOnMainThreadException

来源：https://stackoverflow.com/questions/9413625/android-android-os-networkonmainthreadexception

标签

android

networkonmainthread