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我正在尝试连接到我服务器上的数据库。我刚刚开始使用 AsyncTask，因为它被推荐给我。在此之前，我在主 UI 线程上有 HTTP 请求，这当然意味着它不起作用。它现在工作得更好了，但我仍然遇到问题。如果我的服务器关闭，我会强制关闭。如果您查看下面的代码，我会附上一个祝酒词，告诉我是否无法建立连接。但是，这没有显示。

我需要更改什么以使其停止强制关闭并仅显示敬酒吗？

当我打开服务器并且数据库启动时，我查看了 logcat，我的 android 应用程序确实检索了数据，但它在 logcat 中并且没有显示在页面上。其中一些代码来自教程和搜索谷歌，所以我知道“// PARSING DATA”位现在只计算数据的长度，没有别的。我想那是我需要添加代码才能显示的地方。只是表明这对我来说是多么新鲜。

真的对这一切感到沮丧，这绝对无济于事:(。

这是我的代码：

package com.android.history;

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

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.ParseException;
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.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;

public class CurrentSeasonDrivers extends Activity {

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.currentseason_drivers);

    new HttpTask().execute();

}

private static class HttpTask extends AsyncTask<Void, Void, Void> {
    @Override
    protected void onPreExecute() {

    }

    @Override
    protected Void doInBackground(Void... params) {
        doStuff();

        return null;
    }

    public static void doStuff() {
        JSONArray jArray;
        String result = null;
        InputStream is = null;
        StringBuilder sb = null;
        HttpResponse response;
        HttpEntity entity;

        ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
        // HTTP POST REQUEST
        try {
            HttpClient httpclient = new DefaultHttpClient();

            HttpPost httppost = new HttpPost("http://192.168.0.13/testdatabase.php");

            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            response = httpclient.execute(httppost);

            entity = response.getEntity();

            is = entity.getContent();

        } catch (Exception e) {
            Log.e("log_tag", "Error in http connection" + e.toString());
            Toast.makeText(null, "Could not connect to server", Toast.LENGTH_LONG).show();
        }

        // CONVERT RESPONSE TO STRING
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);
            sb = new StringBuilder();
            sb.append(reader.readLine() + "\n");

            String line;
            while ((line = reader.readLine()) != null) {
                sb.append(line);
            }
            is.close();
            result = sb.toString();

            Log.i("json string", result);
        } catch (Exception e) {
            Log.e("log_tag", "Error converting result " + e.toString());
        }


        // PARSING DATA
        String drivername;
        String drivesfor;
        try {
            jArray = new JSONArray(result);
            JSONObject json_data = null;

            System.out.println("Length " + jArray.length());
            Log.d("DB", "Length " + jArray.length());

            for (int i = 0; i < jArray.length(); i++) {

                System.out.println("counter " + i);
                json_data = jArray.getJSONObject(i);
                drivername = json_data.getString("Driver_full_name");
                drivesfor = json_data.getString("Drives_for");

                System.out.println("Drives_for" + drivesfor);
            }
        } catch (JSONException e1) {
            Log.d("DB", "Error somewhere");
        } catch (ParseException e1) {
            e1.printStackTrace();
        }
    }
}
}

以下是我的 log_cat 中的错误：

08-22 12:26:39.405: E/log_tag(14327): Error in http connectionorg.apache.http.conn.HttpHostConnectException: Connection to http://192.168.0.13 refused
08-22 12:26:39.405: W/dalvikvm(14327): threadid=13: thread exiting with uncaught exception (group=0x40a051f8)
08-22 12:26:39.455: E/AndroidRuntime(14327): FATAL EXCEPTION: AsyncTask #2
08-22 12:26:39.455: E/AndroidRuntime(14327): java.lang.RuntimeException: An error occured while executing doInBackground()
08-22 12:26:39.455: E/AndroidRuntime(14327):    at android.os.AsyncTask$3.done(AsyncTask.java:278)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at java.lang.Thread.run(Thread.java:856)
08-22 12:26:39.455: E/AndroidRuntime(14327): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
08-22 12:26:39.455: E/AndroidRuntime(14327):    at android.os.Handler.<init>(Handler.java:121)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at android.widget.Toast$TN.<init>(Toast.java:317)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at android.widget.Toast.<init>(Toast.java:91)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at android.widget.Toast.makeText(Toast.java:233)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at com.android.history.CurrentSeasonDrivers$HttpTask.doStuff(CurrentSeasonDrivers.java:74)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at com.android.history.CurrentSeasonDrivers$HttpTask.doInBackground(CurrentSeasonDrivers.java:44)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at com.android.history.CurrentSeasonDrivers$HttpTask.doInBackground(CurrentSeasonDrivers.java:1)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at android.os.AsyncTask$2.call(AsyncTask.java:264)
08-22 12:26:39.455: E/AndroidRuntime(14327):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
08-22 12:26:39.455: E/AndroidRuntime(14327):    ... 5 more
4

2 回答 2

1

doInBackground 在单独的线程上运行。您不能显示来自 chaild 线程的 Toast。

在 catch 块内改用以下代码。

 runOnUiThread(new Runnable() {          
   public void run() {                 
    Toast.makeText(null, "Could not connect to server", Toast.LENGTH_LONG).show();     
 }            
});
于 2012-08-22T11:25:34.903 回答
0

Toast 应该通过 UI 线程显示。Android 不允许从后台线程修改 UI。正如 Umesh 建议的那样。

还有一件事可能会导致下一行崩溃

jArray = new JSONArray(result);

如果代码在上述两个异常之后出现在这一行，则此处为result空。

所以你应该在这一行上方添加一个空检查，比如

if(null != result){
     jArray = new JSONArray(result);
}
else{ 
    //Do something else 
      }
于 2012-08-22T11:32:49.087 回答