获取字符串结果后，如何停止在 <AsyncTask> 上扩展的类的 onPostExecute()？

【问题标题】：How to stop onPostExecute() of a class extends on <AsyncTask> after getting the string result?获取字符串结果后，如何停止在 <AsyncTask> 上扩展的类的 onPostExecute()？
【发布时间】：2015-11-20 20:32:55
【问题描述】：

我正在使用连接到在线数据库的 Android 应用程序的登录系统。如果我要显示 onPostExecute() 提供的结果，它可以工作，但如果我要将它放在条件语句上做某事，它就不起作用；或者我应该说，它正在工作，但它正在无限地工作。

得到字符串结果后如何停止执行onPostExecute？

无论如何，这是我的代码：

登录.php

package com.example.navigationdrawerexample;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class Login extends Activity implements OnClickListener, Connector.OnPostExecuteListener{
    EditText studnum;
    EditText pass;
    Button login;
    Button reg;
    TextView errorlog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        studnum = (EditText) findViewById(R.id.studnum);
        pass = (EditText) findViewById(R.id.password);
        login = (Button) findViewById(R.id.login);
        reg = (Button) findViewById(R.id.register);
        errorlog = (TextView) findViewById(R.id.errorlog);
        login.setOnClickListener(this);
    }

    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        if (arg0.getId() == R.id.login){
            ConnectivityManager conv = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo mWifi = conv.getNetworkInfo(ConnectivityManager.TYPE_WIFI);

            if (!(mWifi.isConnected())){
                Toast.makeText(this, "Enable your internet connection first!", Toast.LENGTH_LONG).show();
            } else {
                String student_num = studnum.getText().toString();
                String password = pass.getText().toString();
                Connector connect= new Connector(this,0,"authenticate",0,0,0,student_num,password);
                connect.setOnPostExecuteListener(this);
                connect.execute("");
            }
        }
    }

    @Override
    public void onPostExecute(String result) {


        // TODO Auto-generated method stub


        if (result == "false"){
            errorlog.setText("Incorrect login information..");
        } else if (result == "true"){
            Intent goToLogInMod = new Intent("com.example.navigationdrawerexample.MAINACTIVITY");
            startActivity(goToLogInMod); //para pumunta sa login module
        }

    }
}

Connector.php 如果您注意到一些无用的构造函数参数，请忽略它:)

package com.example.navigationdrawerexample;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URL;
import java.util.ArrayList;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.ProgressDialog;
import android.content.Context;
import android.graphics.Typeface;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup.LayoutParams;
import android.widget.LinearLayout;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class Connector extends AsyncTask<String,Void,String>{
    private OnPostExecuteListener onPostExecuteListener;
    private Context context;
    private int collegeactive;
    private String flag;
    private int spec_art;
    private String response;
    private int month;
    private int yr;
    private String username;
    private String password;

    public Connector(Context context,int college, String flag,int spec_art,int month, int yr,String username, String password){
        this.context = context;
        this.collegeactive = college;
        this.flag = flag;
        this.spec_art = spec_art;
        this.yr = yr;
        this.month = month;
        this.username = username;
        this.password = password;
    }

    public interface OnPostExecuteListener {
        void onPostExecute(String result);
    }

    public void setOnPostExecuteListener(OnPostExecuteListener listener){
        this.onPostExecuteListener = listener;
    }

    protected void onPreExecute(){
        if (flag == "authenticate"){
            Toast.makeText(context, "Please wait...", Toast.LENGTH_LONG).show();
        }

    }


    @Override
    protected String doInBackground(String... arg0) {
        // TODO Auto-generated method stub

        try{
            String link = "";
            if (flag ==  "headline"){
                link = "http://rtu-astronet.com/emag/functions.php?action=printHeadline&coll_id="+collegeactive;
            } else if (flag == "list"){
                link = "http://rtu-astronet.com/emag/functions.php?action=printArticlePerCollege&collegeid="+collegeactive+"&acadornot=1";
            } else if (flag == "spec_article"){
                link = "http://rtu-astronet.com/emag/functions.php?action=printSpecificArticle&articleid="+spec_art;
            } else if (flag == "permonth"){
                link = "http://rtu-astronet.com/emag/functions.php?action=printArticlePerMonth&month="+month+"&year="+yr+"&acadornot=1";
            } else if (flag == "authenticate"){
                link = "http://rtu-astronet.com/emag/functions.php?action=checkAccount&username="+username+"&password="+password;
            }
            URL url = new URL(link);
            HttpClient client = new DefaultHttpClient();
            HttpGet request = new HttpGet();
            request.setURI(new URI(link));
            HttpResponse response = client.execute(request);
            BufferedReader in = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));

            StringBuffer sb = new StringBuffer("");
            String line = "";

            while ((line = in.readLine()) != null) {
                sb.append(line);
                //break;
            }

            in.close();
            return sb.toString();
        } catch(Exception e){
             return new String("Exception: " + e.getMessage());
        }
    }


    @Override
    protected void onPostExecute(String result) {
        if (flag != "authenticate"){
        result = "{ \n \"Data\": \n " + result + " \n }";
        }

        if(onPostExecuteListener !=null){
            onPostExecuteListener.onPostExecute(result);
        }

    }

}

【问题讨论】：

  • 你是说点击登录按钮一次后，onPostExecute()方法会被多次调用？
  • 我认为是这样，或者它被调用了一次但执行永远不会结束。这就是为什么我能够显示数据但不能将其放在条件语句中。
  • 也许你可以在登录活动中打印出字符串结果，看看它是否只被调用过一次，值是否正确。除此之外，我真的不确定这里可能存在什么问题。
  • 请不要使用 StringBuffer，因为它在十多年前被 StringBuilder 取代，即。在 Android 出现之前。

标签： java android android-asynctask


【解决方案1】：

如果我是对的，我认为它与您的听众有关，您永远不会在 onPostExecute 方法中向您的听众返回 false 或 true，但您正在检查登录活动中的 true 或 false 值。 我希望它有帮助

在您的 AsyncTask 中：

protected void onPostExecute(String result) {
    if (flag != "authenticate"){
    result = "{ \n \"Data\": \n " + result + " \n }";
    }

    if(onPostExecuteListener !=null){
        onPostExecuteListener.onPostExecute(result);
    }

}

并且您正在检查登录中的字符串，您正在检查 true 或 false 字符串

【讨论】：

  • 是的，我知道，但我在谈论监听器 onPostExecuteListener.onPostExecute(result);
【解决方案2】：

  1. 创建一个名为 OnPostExecuteListener 的类文件

    公共接口 OnPostExecuteListener { 公共无效 onPostExecute（字符串结果）； }

  2. 在Login类中实现上面创建的接口。

    package com.example.navigationdrawerexample;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class Login extends Activity implements OnClickListener, OnPostExecuteListener {

EditText studnum;
EditText pass;
Button login;
Button reg;
TextView errorlog;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.login);

    studnum = (EditText) findViewById(R.id.studnum);
    pass = (EditText) findViewById(R.id.password);
    login = (Button) findViewById(R.id.login);
    reg = (Button) findViewById(R.id.register);
    errorlog = (TextView) findViewById(R.id.errorlog);
    login.setOnClickListener(this);
}

@Override
public void onClick(View arg0) {
    // TODO Auto-generated method stub
    if (arg0.getId() == R.id.login) {
        ConnectivityManager conv = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo mWifi = conv.getNetworkInfo(ConnectivityManager.TYPE_WIFI);

        if (!(mWifi.isConnected())) {
            Toast.makeText(this, "Enable your internet connection first!", Toast.LENGTH_LONG).show();
        } else {
            String student_num = studnum.getText().toString();
            String password = pass.getText().toString();
            Connector connect = new Connector(Login.this, 0, "authenticate", 0, 0, 0, student_num, password);
            connect.execute("");
        }
    }
}

// this method provides you the result of onPost execute;
@Override
public void onPostExecute(String result) {
    // TODO Auto-generated method stub
    if (result == "false") {
        errorlog.setText("Incorrect login information..");
    } else if (result == "true") {
        Intent goToLogInMod = new Intent("com.example.navigationdrawerexample.MAINACTIVITY");
        startActivity(goToLogInMod); // para pumunta sa login module
    }

}
}

  3. 连接器类

    public class Connector extends AsyncTask<String, Void, String> {

private OnPostExecuteListener onPostExecuteListener;
private Context context;
private int collegeactive;
private String flag;
private int spec_art;
private String response;
private int month;
private int yr;
private String username;
private String password;

public Connector(Context context, int college, String flag, int spec_art, int month, int yr, String username,
        String password) {
    this.context = context;
    this.collegeactive = college;
    this.flag = flag;
    this.spec_art = spec_art;
    this.yr = yr;
    this.month = month;
    this.username = username;
    this.password = password;
}

protected void onPreExecute() {
    if (flag == "authenticate") {
        Toast.makeText(context, "Please wait...", Toast.LENGTH_LONG).show();
    }
    onPostExecuteListener = (OnPostExecuteListener) context;
}

@Override
protected String doInBackground(String... arg0) {
    // TODO Auto-generated method stub

    try {
        String link = "";
        if (flag == "headline") {
            link = "http://rtu-astronet.com/emag/functions.php?action=printHeadline&coll_id=" + collegeactive;
        } else if (flag == "list") {
            link = "http://rtu-astronet.com/emag/functions.php?action=printArticlePerCollege&collegeid="
                    + collegeactive + "&acadornot=1";
        } else if (flag == "spec_article") {
            link = "http://rtu-astronet.com/emag/functions.php?action=printSpecificArticle&articleid=" + spec_art;
        } else if (flag == "permonth") {
            link = "http://rtu-astronet.com/emag/functions.php?action=printArticlePerMonth&month=" + month
                    + "&year=" + yr + "&acadornot=1";
        } else if (flag == "authenticate") {
            link = "http://rtu-astronet.com/emag/functions.php?action=checkAccount&username=" + username
                    + "&password=" + password;
        }
        URL url = new URL(link);
        HttpClient client = new DefaultHttpClient();
        HttpGet request = new HttpGet();
        request.setURI(new URI(link));
        HttpResponse response = client.execute(request);
        BufferedReader in = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));

        StringBuffer sb = new StringBuffer("");
        String line = "";

        while ((line = in.readLine()) != null) {
            sb.append(line);
            // break;
        }

        in.close();
        return sb.toString();
    } catch (Exception e) {
        return new String("Exception: " + e.getMessage());
    }
}

@Override
protected void onPostExecute(String result) {
    if (flag != "authenticate") {
        result = "{ \n \"Data\": \n " + result + " \n }";
    }

    if (onPostExecuteListener != null) {
        onPostExecuteListener.onPostExecute(result);
    }
}
}

【讨论】：

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