Question

我试图在android中的AsyncTask类中从Web读取文本文件，然后将结果传递给静态变量，然后将其加载到另一个类的TextView中，但是我是得到空的结果，无法弄清楚原因。显然，我在代码中弄乱了一些东西......

有人可以评论这个吗？提前谢谢！

package com.example.cuccandroid;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;

import android.os.AsyncTask;

public class readtextfile extends AsyncTask<String, Integer, Void>{

    @Override
    protected Void doInBackground(String... params) {
        try {

               URL url = new URL("http://example.com/example.txt");       

            BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
            String line = null;
            while ((line = in.readLine()) != null) {
                //get lines
                Kezdoh.descriptiontext=line;
            }
            in.close();


            } catch (MalformedURLException e) {

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

                e.printStackTrace();
            }
        return null;
    }

     protected void onProgressUpdate() {
        //called when the background task makes any progress
     }

      protected void onPreExecute() {
         //called before doInBackground() is started
     }
     protected void onPostExecute() {
         //called after doInBackground() has finished 
     }
      }

我的班级，我试图加载

package com.example.cuccandroid;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import com.example.cluppandroid.R;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class Kezdoh extends Fragment{

    TextView description;
    static String descriptiontext;
  @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
          Bundle savedInstanceState) {
          View android = inflater.inflate(R.layout.kezdoh, container, false);
        //GetDescription();
        description = ((TextView)android.findViewById(R.id.description1));

        new readtextfile().execute("http://example.com/example.txt");
        description.setText(descriptiontext);
        return android;
        }   
}

Answer 1

您必须记住AsyncTask在不同的时间在不同的线程中执行。

在你的情况下，description.setText（descriptiontext）;首先执行。

一种好的方法是阻止使用descriptiontext的静态引用。

在这种情况下，您可以做的是向readtextfile添加构造函数并传递TextView实例。 onPostExecute（）方法将在读取字符串内容的doInBackground（）之后执行。随后，应在onPostExecute（）方法中访问任何与UI相关的方法。

我稍微修改了你的readtextfile类，如下所示：

public class readtextfile extends AsyncTask<String, Integer, String>{

private TextView textViewToSet;
public readtextfile(TextView descriptionTextView){
    this.textViewToSet = descriptionTextView;
    }

@Override
protected String doInBackground(String... params) {
    String result = "";
    try {
           URL url = new URL("http://example.com/example.txt");       

        BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
        String line = null;

        while ((line = in.readLine()) != null) {
            //get lines
            result+=line;
        }
        in.close();


        } catch (MalformedURLException e) {

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

            e.printStackTrace();
        }
    return result;
}

 protected void onProgressUpdate() {
    //called when the background task makes any progress
 }

  protected void onPreExecute() {
     //called before doInBackground() is started
 }

@Override
 protected void onPostExecute(String result) {
     this.textViewToSet.setText(result); 
 }
  }

接下来你需要做的就是打电话

new readtextfile().execute("http://example.com/example.txt");

并从onCreateView方法中删除此行

description.setText(descriptiontext);

Answer 2

我已更改了您的asynctask课程，请在TextView被调用后检查并在onpostExecute()中设置super()。请检查以下代码。

public class readtextfile extends AsyncTask<String, String, String> {
        ProgressDialog progressDialog;

        @Override
        protected String doInBackground(String... params) {
            StringBuilder response = new StringBuilder();
            try {

                URL url = new URL(
                        "http://example.com/example.txt");

                BufferedReader in = new BufferedReader(new InputStreamReader(
                        url.openStream()));
                String line = null;
                while ((line = in.readLine()) != null) {
                    // get lines
                    response.append(line);

                }
                in.close();
            } catch (MalformedURLException e) {

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

                e.printStackTrace();
            }
            return response.toString();
        }

        protected void onProgressUpdate() {
            // called when the background task makes any progress
        }

        protected void onPreExecute() {
            progressDialog = new ProgressDialog(MainActivity.this);
            progressDialog.show();
        }

        @Override
        protected void onPostExecute(String result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            progressDialog.dismiss();

            Log.d("tag", "Response is " + result.toString());
        //set your Textview here
        description.setText(result.toString());
        }
    }

您的主要班级

package com.example.cuccandroid;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import com.example.cluppandroid.R;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class Kezdoh extends Fragment{

    TextView description;
    static String descriptiontext;
  @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
          Bundle savedInstanceState) {
          View android = inflater.inflate(R.layout.kezdoh, container, false);
        //GetDescription();
        description = ((TextView)android.findViewById(R.id.description1));

        new readtextfile().execute("http://example.com/example.txt");

        return android;
        }   
}

试图在Android中的AsyncTask中读取文本文件，但我得到空结果

2 个答案: