下载json并设置适配器后，ArrayList为空

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解决

     

我试图从json url中保存img url，我有点卡在这里。请帮忙 我是android开发的新手，很抱歉，如果这是一个noob问题。谢谢！

public class images {

private ArrayList<String> url;
private String TAG = "Array list";


public images() {

  url = new ArrayList<>();
    new setupJson().execute("https://wallapp.000webhostapp.com");
}

public ArrayList<String> getImages() {
    return url;
}

public String getOneImage(int position) {
    return url.get(position);
}


public class setupJson extends AsyncTask<String, String, String> {
    @Override
    protected String doInBackground(String... strings) {

        // Http connection
        HttpURLConnection connection = null;
        BufferedReader reader = null;

        try {
            URL urlConn = new URL(strings[0]);

            connection = (HttpURLConnection) urlConn.openConnection();
            connection.connect();

            InputStream istream = connection.getInputStream();

            reader = new BufferedReader(new InputStreamReader(istream));

            StringBuffer buffer = new StringBuffer();
            String line = "";
            while((line = reader.readLine()) != null) {
                buffer.append(line+"\n");
            }
            return buffer.toString();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(connection != null) {
                connection.disconnect();
            }
            try {
                if(reader != null) {
                    reader.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }


        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);

       // Log.e(TAG,"Result: "+result);


        try {
    JSONObject jsonObj = new JSONObject(result);

    // Getting JSON Array node
    JSONArray imgs = jsonObj.getJSONArray("img");


    for (int i = 0; i < imgs.length(); i++) {
        JSONObject url_img = imgs.getJSONObject(i);
        String get_url = url_img.getString("url");
        //String get_cat = url_img.getString("category");

        url.add(get_url);

    }

} catch (final JSONException e)
{
    Log.e(TAG, "Json parsing error: " + e.getMessage());
}
    }

在for循环之后，如果我记录url变量，它会显示值，但之后 new setupJson（）。execute（）; 当我记录url时它显示为空（即[]）

已更新

感谢@Selvin我弄清楚我修复的代码是什么问题，将setupJson类移动到mainactivity和onPostExecute我设置了适配器。

MainAcitivity

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

    gridView = (GridView) findViewById(R.id.gridview);

    new setupJson().execute();

    gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
            String image_url = image.getOneImage(i);
            Intent intent = new Intent(MainActivity.this,WallImage.class);
            intent.putExtra("url",image_url);
            startActivity(intent);
            //Toast.makeText(getApplicationContext(),image_url,Toast.LENGTH_LONG).show();
        }
    });



}

public class setupJson extends AsyncTask<Void, Void, Void> {
    @Override
    protected Void doInBackground(Void... arg0) {

        HttpHandler sh = new HttpHandler();
        String url = "https://wallapp.000webhostapp.com";

        String jsonStr = sh.makeServiceCall(url);


        try {
            JSONObject jsonObj = new JSONObject(jsonStr);

            // Getting JSON Array node
            JSONArray imgs = jsonObj.getJSONArray("img");


            for (int i = 0; i < imgs.length(); i++) {
                JSONObject url_img = imgs.getJSONObject(i);
                String get_url = "https://wallapp.000webhostapp.com/"+url_img.getString("url");
                //String get_cat = url_img.getString("category");
                image.url.add(get_url);
            }




        } catch (final JSONException e)
        {
            Log.e(TAG, "Json parsing error: " + e.getMessage());
        }


        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);

        gridView.setAdapter(new ImageAdapter(MainActivity.this));

    }


}
}