Question

我是Android的新手，我希望有人可以帮助我。我有一个活动教员和一个按钮。

这是我的XML布局browse_faculty：

<Button
    android:onClick="searchFSTEHandler"
    android:id="@+id/bFSTE"
    android:layout_width="220dp"
    android:layout_height="80dp"
    android:layout_alignLeft="@+id/bFBE"
    android:layout_below="@+id/bFBE"
    android:layout_marginTop="20dp"
    android:text="@string/fste" />

这是我的教师活动，显示按钮：我使用Intent来查看ListView

public class Faculty extends Activity{

    @Override
    protected void onCreate(Bundle BrowseFaculty) {
        // TODO Auto-generated method stub
        super.onCreate(BrowseFaculty);
        setContentView(R.layout.browse_faculty);
    }

    //on the XML,this is the "searchFSTEHandler" i want to use to show ListView
    public void searchFSTEHandler(View target){
        Intent courseList = new Intent(this, HttpActivity.class);
        startActivity(courseList);
    }
}

以下是“HttpActivity”类是显示我的ListView的类。这个类读取一个php文件，该文件从MySQL服务器获取数据并转换为JSON数据，然后将其解析为数组列表。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;



import android.os.AsyncTask;
import android.os.Bundle;
import android.app.ListActivity;
import android.widget.ArrayAdapter;

public class HttpActivity extends ListActivity {

public String f1 = "FSTE";




@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.faculty_course);


    new getHttp().execute();

    getHttp test =new getHttp();


    String strJsonData = test.doInBackground(f1);

    // Convert String JSON data to Java class
    ArrayList<Courses> arrayCourse= test.parseJsonData(strJsonData);

    //Create an ArrayAdapter which shows the ArrayList data
    this.setListAdapter(new ArrayAdapter<Courses>(this,android.R.layout.simple_list_item_1,arrayCourse));



}




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

  public getHttp() { 











  }

  @Override
    protected String doInBackground(String... faculty) {



    InputStream is = null;
    try {
        URL url = new URL("http://10.0.2.2/sqlWebService.php?faculty=FSTE");
        URLConnection con = url.openConnection();
        con.setConnectTimeout(10000);
        con.setReadTimeout(10000);
        is = con.getInputStream();

        BufferedReader br = new BufferedReader(
                new InputStreamReader(is));
        StringBuffer sb = new StringBuffer();
        String str;
        while ((str = br.readLine()) != null) {
            sb.append(str);
        }
        return sb.toString();

    } catch (IOException e) {
        e.printStackTrace();
        return "";

    } finally {
        try {
            if (is != null)
                is.close();
        } catch (IOException e2) {
            e2.printStackTrace();
        }
    }


}

//------------------------------------------------------  
  private ArrayList<Courses> parseJsonData(String strJson) {
        ArrayList<Courses> Course = new ArrayList<Courses>();

        try {
            // Generate JSONArray object by JSON String data
            JSONArray arr = new JSONArray(strJson);

            //from the JSONArray, get one element (row) of JSONData
            for (int i = 0; i < arr.length(); i++) {

                //Get JSON Object which is one element of the array
                JSONObject ob = arr.getJSONObject(i);

                Courses exam = new Courses();
                //get the value by key, and set to exam class
                exam.setCode(ob.optString("code"));

                //save exam class to exam array list
                Course.add(exam);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return Course;
    }





 }









 }

单击按钮后应用程序崩溃并出错： “android.os.NetworkOnMainThreadException”

请帮助！

Answer 1

您遇到的问题是网络操作，就像您尝试做的那样，不能也不应该在主UI线程上执行。这样做会导致 ANR（Android无响应），这正是您刚刚获得的错误。您要执行的操作是将代码移至单独的主题或 AsyncTask ，以便使用 doInBackground()在后台的其他主题上执行此操作方法，无法访问主UI线程上的视图。例如，

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

    public ExampleOperation() { //ctor }

    @Override
    protected void onPreExecute() {
        //things that you want to initialize and maybe show dialog to user.
    }

    @Override
    protected String doInBackground(String... params) {
       //this is where you perform that network related operation.  
    }

    @Override
    protected void onPostExecute(String result) {
       //this is where get the results from the network related task.
    }

    @Override
    protected void onProgressUpdate(Void... values) {
       //you can update your progressbar if any; otherwise omit method.
    }

}

然后你要做的就是调用AsyncTask你想要使用它的地方：new ExampleOperation().execute();

Answer 2

您不能在主线程中进行HTTP调用，它们需要太长时间并且会使UI无响应。您需要在AsyncTask中执行此操作。

按钮单击时显示ListView

2 个答案: