Question

我正在开发一个基于远程数据库的Android应用程序，我找到了如何将数据放入数据库的解决方案，但是我遇到了很多问题。当我打开获取数据的活动时，应用程序崩溃。我无法本地化我的代码中的错误！所以这是我的代码，我希望你能帮助我。谢谢。

这是“Acceuil”类，有1个按钮可以打开“教授”类。

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;


//in this class I'm just defining a button that will open another class to get data from the database.

public class Acceuil extends Activity  {
	
	
	Button b1;
	

	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		setContentView(R.layout.acceuil);
		
		b1 = (Button) findViewById(R.id.button3);
		
		b1.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View arg0) {
				// TODO Auto-generated method stub
			
				Intent i = new Intent(getApplicationContext(), Professors.class);
				startActivity(i);
				
			}
		});
		
		
		
		
		

	}
}

这是崩溃我的应用程序的“教授”课程。

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class Professors extends Activity {
	
	
	
	//URL to get JSON Array
		private static  String url = "http://waelhamda.host22.com/comments.php";
		
		//JSON Node Names 
		private static final String TAG_USER = "posts";
		private static final String TAG_ID = "last";
		
		
		JSONArray user = null;



	    @Override
	    protected void onCreate(Bundle savedInstanceState) {
	        super.onCreate(savedInstanceState);
	      
	        setContentView(R.layout.professors);
	        
			// Creating new JSON Parser
			JSONParser jParser = new JSONParser();

			// Getting JSON from URL
			JSONObject json = jParser.getJSONFromUrl(url);
			
			try {
				// Getting JSON Array
				user = json.getJSONArray(TAG_USER);
				JSONObject c = user.getJSONObject(0);
				
				// Storing  JSON item in a Variable
				String id = c.getString(TAG_ID);
			
				
				//Importing TextView
				final TextView uid = (TextView)findViewById(R.id.pro1);
			
				
				//Set JSON Data in TextView
				uid.setText(id);
				

			
		} catch (JSONException e) {
			e.printStackTrace();
		}

				

	    }


	 
	    
	}

这是“JSONParser”类。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;
 
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;


 
import android.util.Log;
 
public class JSONParser {
 
    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";
 
    // constructor
    public JSONParser() {
 
    }
 
    
    
    
   

    	public JSONObject getJSONFromUrl(String url) {

    		// Making HTTP request
    		try {
    			// defaultHttpClient
    			DefaultHttpClient httpClient = new DefaultHttpClient();
    			HttpPost httpPost = new HttpPost(url);

    			HttpResponse httpResponse = httpClient.execute(httpPost);
    			HttpEntity httpEntity = httpResponse.getEntity();
    			is = httpEntity.getContent();			

    		} catch (UnsupportedEncodingException e) {
    			e.printStackTrace();
    		} catch (ClientProtocolException e) {
    			e.printStackTrace();
    		} catch (IOException e) {
    			e.printStackTrace();
    		}
    		
    		try {
    			BufferedReader reader = new BufferedReader(new InputStreamReader(
    					is, "iso-8859-1"), 8);
    			StringBuilder sb = new StringBuilder();
    			String line = null;
    			while ((line = reader.readLine()) != null) {
    				sb.append(line + "\n");
    			}
    			is.close();
    			json = sb.toString();
    		} catch (Exception e) {
    			Log.e("Buffer Error", "Error converting result " + e.toString());
    		}

    		// try parse the string to a JSON object
    		try {
    			jObj = new JSONObject(json);
    		} catch (JSONException e) {
    			Log.e("JSON Parser", "Error parsing data " + e.toString());
    		}

    		// return JSON String
    		return jObj;

    	}
    
    
    
    
    
    
    
    // function get json from url
    // by making HTTP POST or GET mehtod
    public JSONObject makeHttpRequest(String url, String method,
            List<NameValuePair> params) {
 
        // Making HTTP request
        try {
 
            // check for request method
            if(method == "POST"){
                // request method is POST
                // defaultHttpClient
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));
 
                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
 
            }else if(method == "GET"){
                // request method is GET
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url);
 
                HttpResponse httpResponse = httpClient.execute(httpGet);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
            }           
 
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
 
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }
 
        // try parse the string to a JSON object
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }
 
        // return JSON String
        return jObj;
 
    }

	
}

最后这是应用程序的清单文件。

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.wael.enimcommunity"
    android:versionCode="1"
    android:versionName="1.0" >
    
    
<meta-data android:name="com.google.android.backup.api_key" 
        android:value="AEdPqrEAAAAIdPJ8uLgoiErqlZNYU5_jN_d8O8VPPtfbbF5MRQ" />


    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="21" />
    
     <uses-permission android:name="android.permission.INTERNET"/>

    <uses-permission 
        android:name="android.permission.ACCESS_FINE_LOCATION" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.wael.enimcommunity.Login"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.wael.enimcommunity.Register"
            android:label="@string/app_name"  >
        </activity>
        <activity
            android:name="com.wael.enimcommunity.Acceuil"
            android:label="@string/app_name"  >
        </activity>
        <activity
            android:name="com.wael.enimcommunity.JSONParser"
            android:label="@string/app_name"  >
        </activity>
        <activity
            android:name="com.wael.enimcommunity.GPSTracker"
            android:label="@string/app_name"  >
        </activity>
        <activity
            android:name="com.wael.enimcommunity.Events"
            android:label="@string/app_name"  >
        </activity>
        <activity
            android:name="com.wael.enimcommunity.Professors"
            android:label="@string/app_name"  >
        </activity>

        <activity
            android:name="com.wael.enimcommunity.Portail"
            android:label="@string/app_name"  >
        </activity>
        <activity
            android:name="com.wael.enimcommunity.Schedule"
            android:label="@string/app_name"  >
        </activity>
    </application>

</manifest>

我希望这些信息足以解决我的问题。再次谢谢我的朋友。

Answer 1

您是主线程中的网络。你需要先解决这个问题。

使用AsyncTask

示例：

private TextView uid; // Define global

在onCreate

uid = (TextView)findViewById(R.id.pro1);

new MyAsyncTask().execute();

内心课

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

 @Override
 public String doInBackground(Void a) {
            JSONParser jParser = new JSONParser();

            // Getting JSON from URL
            JSONObject json = jParser.getJSONFromUrl(url);

        try {
                // Getting JSON Array
                user = json.getJSONArray(TAG_USER);
                JSONObject c = user.getJSONObject(0);

                // Storing  JSON item in a Variable
                String id = c.getString(TAG_ID);

                return id;
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
 }

 public void onPostExecute(String result) {
    uid.setText(result);
 }

}

Answer 2

网络运营可能涉及不可预测的延迟。为防止此操作导致糟糕的用户体验，请始终在UI的单独线程上执行网络操作。 AsyncTask类提供了从UI线程启动新任务的最简单方法之一。

Connecting to the Network

从我的URL解析JSON数据时出错

2 个答案: