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java - 如何为 android 的连接 json 调用创建线程

转载 作者:行者123 更新时间:2023-11-30 04:04:51 25 4
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我在第 97 行收到此错误 java.lang.NullPointerException

我认为是为了 de json 调用,因为没有获取数据,

我如何创建一个线程,首先获取这些数据然后执行下一步。

我在这方面真的很新,所以任何帮助我们都很感激。

package com.zoada;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

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.app.Activity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.Window;
import android.view.WindowManager;
import android.widget.TableLayout;
import android.widget.TableRow;
import android.widget.TextView;



public class MainActivity extends Activity {

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

// esconde el titlebar de la aplicaci�n
// tiene que estar antes de colocar el mainLayout
requestWindowFeature(Window.FEATURE_NO_TITLE);
// esconde el statusbar de Android
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.activity_main);

JSONArray posiciones = null;

// *** Comienza la comunicaci�n con el servidor

BufferedReader in = null;
try {
HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet("http://zoada.com/blah.php");
HttpResponse response = client.execute(request);


// leyendo "response" un string gigantesco
in = new BufferedReader(
new InputStreamReader(
response.getEntity().getContent()));

// imprimpiendo el tarugo de texto linea a linea

StringBuffer sb = new StringBuffer("");
String line = "";
String NL = System.getProperty("line.separator");
while ((line = in.readLine()) != null) {
sb.append(line + NL);
}
in.close();

String page = sb.toString();
//System.out.println(page);

//aqui viene la parte JSON!!!

JSONObject jObject = new JSONObject(page);
posiciones = jObject.getJSONArray("positions");

for (int i=0; i< posiciones.length(); i++) {
JSONObject jo = posiciones.getJSONObject(i);
//System.out.println(jo.getString("name"));
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (in != null) {
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

// *** termina comunicaci�n con el servidor


TableLayout tl = (TableLayout)findViewById(R.id.containerTable);
LayoutInflater inflater = getLayoutInflater();

for (int i = 0; i < posiciones.length(); i++) {
try {
JSONObject jo = posiciones.getJSONObject(i);

TableRow row = (TableRow)inflater.inflate(R.layout.tablerow, tl, false);

TextView pos = (TextView)row.findViewById(R.id.position);
String posTxt=jo.getString("position");
pos.setText(posTxt);

TextView team = (TextView)row.findViewById(R.id.team);
String teamTxt=jo.getString("name");
team.setText(teamTxt);

TextView points = (TextView)row.findViewById(R.id.points);
String pointsTxt=jo.getString("points");
points.setText(pointsTxt);

TextView games = (TextView)row.findViewById(R.id.games);
String gamesTxt=jo.getString("played");
games.setText(gamesTxt);

TextView victories = (TextView)row.findViewById(R.id.victories);
String victoriesTxt=jo.getString("won");
victories.setText(victoriesTxt);

TextView draw = (TextView)row.findViewById(R.id.draw);
String drawsTxt=jo.getString("draw");
draw.setText(drawsTxt);

TextView lost = (TextView)row.findViewById(R.id.loss);
String loseTxt=jo.getString("lost");
lost.setText(loseTxt);

TextView goals = (TextView)row.findViewById(R.id.goals);
int goalsInt = Integer.parseInt(jo.getString("gol"));
int againstInt = Integer.parseInt(jo.getString("against"));
String goalsTxt=goalsInt+":"+againstInt;
goals.setText(goalsTxt);

TextView diff = (TextView)row.findViewById(R.id.difference);
int diffInt=goalsInt-againstInt;
String diffTxt=""+diffInt;
diff.setText(diffTxt);
/**/
tl.addView(row);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

// text = (EditText) findViewById(R.id.EditText01);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}

最佳答案

您不应该在 UI 线程中执行网络操作!例如,您可以在您的类(class)中创建 AsyncTask。它可能看起来类似于此

   private class ParseTask extends AsyncTask<Params, Progress, Result> {
@Override
protected Result doInBackground(Params params) {
// get url
Params url = params[0];
// create HttpClient etc.
...
// get response, and parse json
// return
return result;
}

@Override
protected void onPostExecute (Result result) {
// now when you have result from parsed json,
// update application UI or whatever you need
someEditText.setText(value_from_result);
}
}

然后调用onCreate方法

ParseTask task = new ParseTask();
task.execute(url);

启动 AsyncTask。

另一方面,也可以在IntentService中处理json,或者一般的服务,解析后的json通过广播返回给Activity,也可以达到同样的效果。

关于java - 如何为 android 的连接 json 调用创建线程,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/11870864/

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