java - JSONArray在Android中将对象转换为数组找不到标签

Question

我正在尝试通过 Android 上的 JSON 从 API 中提取信息。我已经成功下载了信息，现在我需要将其放入带有“类别”标签的 JSONArray 中。最终这将进入 ListView 。这是我的代码:

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.StatusLine;
import org.apache.http.client.ClientProtocolException;
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.util.Log;


public class jsonParser {

    //initialize
    static JSONObject object =null;

    public jsonParser(){

    }

     public JSONObject getJSONfromURL (String url){
            //HTTP call
            try{
                URLConnection connection = new URL(url).openConnection();

                BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()), 2048 * 16);
                StringBuffer builder = new StringBuffer();
                String line;

                while ((line = reader.readLine()) != null) {
                  builder.append(line).append("\n");
                }
                String blah = builder.toString();

                //Parsing string into JSONArray
                JSONObject object = new JSONObject ( new String(builder.toString()) );
                Log.e("success","created object: " + object);

                } catch(Exception e){
                    Log.e("Http Error","Error in http connection " + e.toString());

                }


            return object;
        }
}

这是 Logcat:

05-12 16:57:54.040: E/success(9625): created object: {"Categories":[{"id":"2","name":"Glass Repair"},{"id":"3","name":"Appliance Repair"},{"id":"4","name":"Air Conditioning"},{"id":"5","name":"Community Involvement"},{"id":"6","name":"Electrical"},{"id":"7","name":"Flooring"},{"id":"8","name":"Heating Repair"},{"id":"9","name":"Landscaping"},{"id":"10","name":"Plumbing"},{"id":"11","name":"Remodeling\/Renovation"},{"id":"12","name":"Window Coverings"}]}
05-12 16:57:54.040: E/JSON Variable(9625): json returns this value: null
05-12 16:57:54.070: E/Test JSON(9625): JSON s returns: null
05-12 16:57:54.070: W/dalvikvm(9625): threadid=1: thread exiting with uncaught exception (group=0x416bf438)
05-12 16:57:54.070: E/AndroidRuntime(9625): FATAL EXCEPTION: main
05-12 16:57:54.070: E/AndroidRuntime(9625): java.lang.NullPointerException
05-12 16:57:54.070: E/AndroidRuntime(9625):     at com.example.hstnc_activity.DisplayServiceActivity$Request.onPostExecute(DisplayServiceActivity.java:104)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at com.example.hstnc_activity.DisplayServiceActivity$Request.onPostExecute(DisplayServiceActivity.java:1)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at android.os.AsyncTask.finish(AsyncTask.java:631)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at android.os.AsyncTask.access$600(AsyncTask.java:177)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at android.os.Looper.loop(Looper.java:137)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at android.app.ActivityThread.main(ActivityThread.java:4918)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at java.lang.reflect.Method.invokeNative(Native Method)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at java.lang.reflect.Method.invoke(Method.java:511)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)
05-12 16:57:54.070: E/AndroidRuntime(9625):     at dalvik.system.NativeStart.main(Native Method)

最后这是 JSON 信息(使用 jsonlint.com 获取):

{
    "Categories": [
        {
            "id": "2",
            "name": "Glass Repair"
        },
        {
            "id": "3",
            "name": "Appliance Repair"
        },
        {
            "id": "4",
            "name": "Air Conditioning"
        },
        {
            "id": "5",
            "name": "Community Involvement"
        },
        {
            "id": "6",
            "name": "Electrical"
        },
        {
            "id": "7",
            "name": "Flooring"
        },
        {
            "id": "8",
            "name": "Heating Repair"
        },
        {
            "id": "9",
            "name": "Landscaping"
        },
        {
            "id": "10",
            "name": "Plumbing"
        },
        {
            "id": "11",
            "name": "Remodeling/Renovation"
        },
        {
            "id": "12",
            "name": "Window Coverings"
        }
    ]
}

这是异步方法:

public class Request extends AsyncTask<String, Void, JSONObject> {

    private static final int REGISTRATION_TIMEOUT = 3 * 1000;
    private static final int WAIT_TIMEOUT = 30 * 1000;
    private ProgressDialog dialog = 
            new ProgressDialog(DisplayServiceActivity.this);


    protected void onPreExecute() {
        dialog = new ProgressDialog(DisplayServiceActivity.this);
        dialog.setMessage("Getting your info real quick... Please wait...");
        dialog.show();
    }

    protected JSONObject doInBackground(String... params) {

        json = jParser.getJSONfromURL(url);
        Log.e("JSON Variable", "json returns this value: " + json);

        return json;

    }

    protected void onPostExecute(JSONObject s) {          
        super.onPostExecute(s);

        dialog.dismiss();
        Log.e("Test JSON","JSON s returns: " + s);
        try {
            directory = s.getJSONArray("Categories");
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        for(int i = 0; i< directory.length(); i++){
            String str_id = directory.optString(i, "id");
            String str_name = directory.optString(i, "name");
            displayCatList(str_id, str_name);

            Log.e("Test directory","Directory returns: " + json);
        }

    }

}

感谢所有的帮助!

Answer 1

您需要从 getJSONFromURL() 方法返回 data 对象。

现在在 doInBackground() 中执行此操作->

JSONArray categories = data.getJSONArray("Categories");

现在您将拥有类别数组。

您需要在 onPreExecute 下初始化您的dialog，如下所示 ->

protected void onPreExecute() {
    dialog = new ProgressDialog(DisplayServiceActivity.this);
    dialog.setMessage("Getting your info real quick... Please wait...");
    dialog.show();
}

执行此操作 ->

public JSONObject getJSONfromURL (String url){
        //HTTP call
        JSONObject object = new JSONObject();
        try{
            URLConnection connection = new URL(url).openConnection();

            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()), 2048 * 16);
            StringBuffer builder = new StringBuffer();
            String line;

            while ((line = reader.readLine()) != null) {
              builder.append(line).append("\n");
            }
            String blah = builder.toString();

            //Parsing string into JSONArray
            object = new JSONObject ( new String(builder.toString()) );
            Log.e("success","created object: " + object);

            } catch(Exception e){
                Log.e("Http Error","Error in http connection " + e.toString());

            }


        return object;
    }