Question

运行下面的代码后，我总是得到一个空白屏幕。我已经创建了一个自定义数组适配器和一个自定义类，但是当我使用数组列表在列表视图中显示项目时，它没有给出任何空白屏幕。但现在我想测试解析使用Json数据现在它给出一个空白屏幕，为什么请帮助

    import android.util.Log;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;

/**
 * Helper methods related to requesting and receiving earthquake data from USGS.
 */
public final class QueryUtils {

    /** Sample JSON response for a USGS query */
    private static final String SAMPLE_JSON_RESPONSE = "{\"type\":\"FeatureCollection\",\"metadata\":{\"generated\":1462295443000,\"url\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&starttime=2016-01-01&endtime=2016-01-31&minmag=6&limit=10\",\"title\":\"USGS Earthquakes\",\"status\":200,\"api\":\"1.5.2\",\"limit\":10,\"offset\":1,\"count\":10},\"features\":[{\"type\":\"Feature\",\"properties\":{\"mag\":7.2,\"place\":\"88km N of Yelizovo, Russia\",\"time\":1454124312220,\"updated\":1460674294040,\"tz\":720,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us20004vvx\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us20004vvx&format=geojson\",\"felt\":2,\"cdi\":3.4,\"mmi\":5.82,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":1,\"sig\":798,\"net\":\"us\",\"code\":\"20004vvx\",\"ids\":\",at00o1qxho,pt16030050,us20004vvx,gcmt20160130032510,\",\"sources\":\",at,pt,us,gcmt,\",\"types\":\",cap,dyfi,finite-fault,general-link,general-text,geoserve,impact-link,impact-text,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,tectonic-summary,\",\"nst\":null,\"dmin\":0.958,\"rms\":1.19,\"gap\":17,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 7.2 - 88km N of Yelizovo, Russia\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[158.5463,53.9776,177]},\"id\":\"us20004vvx\"},\n" +
            "{\"type\":\"Feature\",\"properties\":{\"mag\":6.1,\"place\":\"94km SSE of Taron, Papua New Guinea\",\"time\":1453777820750,\"updated\":1460156775040,\"tz\":600,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us20004uks\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us20004uks&format=geojson\",\"felt\":null,\"cdi\":null,\"mmi\":4.1,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":1,\"sig\":572,\"net\":\"us\",\"code\":\"20004uks\",\"ids\":\",us20004uks,gcmt20160126031023,\",\"sources\":\",us,gcmt,\",\"types\":\",cap,geoserve,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,tectonic-summary,\",\"nst\":null,\"dmin\":1.537,\"rms\":0.74,\"gap\":25,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 6.1 - 94km SSE of Taron, Papua New Guinea\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[153.2454,-5.2952,26]},\"id\":\"us20004uks\"},\n" +
            "{\"type\":\"Feature\",\"properties\":{\"mag\":6.3,\"place\":\"50km NNE of Al Hoceima, Morocco\",\"time\":1453695722730,\"updated\":1460156773040,\"tz\":0,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us10004gy9\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us10004gy9&format=geojson\",\"felt\":117,\"cdi\":7.2,\"mmi\":5.28,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":0,\"sig\":695,\"net\":\"us\",\"code\":\"10004gy9\",\"ids\":\",us10004gy9,gcmt20160125042203,\",\"sources\":\",us,gcmt,\",\"types\":\",cap,dyfi,geoserve,impact-text,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,tectonic-summary,\",\"nst\":null,\"dmin\":2.201,\"rms\":0.92,\"gap\":20,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 6.3 - 50km NNE of Al Hoceima, Morocco\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[-3.6818,35.6493,12]},\"id\":\"us10004gy9\"},\n" +
            "{\"type\":\"Feature\",\"properties\":{\"mag\":7.1,\"place\":\"86km E of Old Iliamna, Alaska\",\"time\":1453631430230,\"updated\":1460156770040,\"tz\":-540,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us10004gqp\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us10004gqp&format=geojson\",\"felt\":1816,\"cdi\":7.2,\"mmi\":6.6,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":1,\"sig\":1496,\"net\":\"us\",\"code\":\"10004gqp\",\"ids\":\",at00o1gd6r,us10004gqp,ak12496371,gcmt20160124103030,\",\"sources\":\",at,us,ak,gcmt,\",\"types\":\",cap,dyfi,finite-fault,general-link,general-text,geoserve,impact-link,impact-text,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,tectonic-summary,trump-origin,\",\"nst\":null,\"dmin\":0.72,\"rms\":2.11,\"gap\":19,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 7.1 - 86km E of Old Iliamna, Alaska\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[-153.4051,59.6363,129]},\"id\":\"us10004gqp\"},\n" +
            "{\"type\":\"Feature\",\"properties\":{\"mag\":6.6,\"place\":\"215km SW of Tomatlan, Mexico\",\"time\":1453399617650,\"updated\":1459963829040,\"tz\":-420,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us10004g4l\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us10004g4l&format=geojson\",\"felt\":11,\"cdi\":2.7,\"mmi\":3.92,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":1,\"sig\":673,\"net\":\"us\",\"code\":\"10004g4l\",\"ids\":\",at00o1bebo,pt16021050,us10004g4l,gcmt20160121180659,\",\"sources\":\",at,pt,us,gcmt,\",\"types\":\",cap,dyfi,geoserve,impact-link,impact-text,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,tectonic-summary,\",\"nst\":null,\"dmin\":2.413,\"rms\":0.98,\"gap\":74,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 6.6 - 215km SW of Tomatlan, Mexico\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[-106.9337,18.8239,10]},\"id\":\"us10004g4l\"},\n" +
            "{\"type\":\"Feature\",\"properties\":{\"mag\":6.7,\"place\":\"52km SE of Shizunai, Japan\",\"time\":1452741933640,\"updated\":1459304879040,\"tz\":540,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us10004ebx\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us10004ebx&format=geojson\",\"felt\":51,\"cdi\":5.8,\"mmi\":6.45,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":1,\"sig\":720,\"net\":\"us\",\"code\":\"10004ebx\",\"ids\":\",us10004ebx,pt16014050,at00o0xauk,gcmt20160114032534,\",\"sources\":\",us,pt,at,gcmt,\",\"types\":\",associate,cap,dyfi,geoserve,impact-link,impact-text,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,\",\"nst\":null,\"dmin\":0.281,\"rms\":0.98,\"gap\":22,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 6.7 - 52km SE of Shizunai, Japan\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[142.781,41.9723,46]},\"id\":\"us10004ebx\"},\n" +
            "{\"type\":\"Feature\",\"properties\":{\"mag\":6.1,\"place\":\"12km WNW of Charagua, Bolivia\",\"time\":1452741928270,\"updated\":1459304879040,\"tz\":-240,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us10004ebw\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us10004ebw&format=geojson\",\"felt\":3,\"cdi\":2.2,\"mmi\":2.21,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":0,\"sig\":573,\"net\":\"us\",\"code\":\"10004ebw\",\"ids\":\",us10004ebw,gcmt20160114032528,\",\"sources\":\",us,gcmt,\",\"types\":\",cap,dyfi,geoserve,impact-text,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,tectonic-summary,\",\"nst\":null,\"dmin\":5.492,\"rms\":1.04,\"gap\":16,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 6.1 - 12km WNW of Charagua, Bolivia\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[-63.3288,-19.7597,582.56]},\"id\":\"us10004ebw\"},\n" +
            "{\"type\":\"Feature\",\"properties\":{\"mag\":6.2,\"place\":\"74km NW of Rumoi, Japan\",\"time\":1452532083920,\"updated\":1459304875040,\"tz\":540,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us10004djn\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us10004djn&format=geojson\",\"felt\":8,\"cdi\":3.4,\"mmi\":3.74,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":0,\"sig\":594,\"net\":\"us\",\"code\":\"10004djn\",\"ids\":\",us10004djn,gcmt20160111170803,\",\"sources\":\",us,gcmt,\",\"types\":\",cap,dyfi,geoserve,impact-text,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,tectonic-summary,\",\"nst\":null,\"dmin\":1.139,\"rms\":0.96,\"gap\":33,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 6.2 - 74km NW of Rumoi, Japan\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[141.0867,44.4761,238.81]},\"id\":\"us10004djn\"},\n" +
            "{\"type\":\"Feature\",\"properties\":{\"mag\":6.5,\"place\":\"227km SE of Sarangani, Philippines\",\"time\":1452530285900,\"updated\":1459304874040,\"tz\":480,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us10004dj5\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us10004dj5&format=geojson\",\"felt\":1,\"cdi\":2.7,\"mmi\":7.5,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":1,\"sig\":650,\"net\":\"us\",\"code\":\"10004dj5\",\"ids\":\",at00o0srjp,pt16011050,us10004dj5,gcmt20160111163807,\",\"sources\":\",at,pt,us,gcmt,\",\"types\":\",cap,dyfi,geoserve,impact-link,impact-text,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,tectonic-summary,\",\"nst\":null,\"dmin\":3.144,\"rms\":0.72,\"gap\":22,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 6.5 - 227km SE of Sarangani, Philippines\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[126.8621,3.8965,13]},\"id\":\"us10004dj5\"},\n" +
            "{\"type\":\"Feature\",\"properties\":{\"mag\":6,\"place\":\"Pacific-Antarctic Ridge\",\"time\":1451986454620,\"updated\":1459202978040,\"tz\":-540,\"url\":\"http://earthquake.usgs.gov/earthquakes/eventpage/us10004bgk\",\"detail\":\"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us10004bgk&format=geojson\",\"felt\":0,\"cdi\":1,\"mmi\":0,\"alert\":\"green\",\"status\":\"reviewed\",\"tsunami\":0,\"sig\":554,\"net\":\"us\",\"code\":\"10004bgk\",\"ids\":\",us10004bgk,gcmt20160105093415,\",\"sources\":\",us,gcmt,\",\"types\":\",cap,dyfi,geoserve,losspager,moment-tensor,nearby-cities,origin,phase-data,shakemap,\",\"nst\":null,\"dmin\":30.75,\"rms\":0.67,\"gap\":71,\"magType\":\"mww\",\"type\":\"earthquake\",\"title\":\"M 6.0 - Pacific-Antarctic Ridge\"},\"geometry\":{\"type\":\"Point\",\"coordinates\":[-136.2603,-54.2906,10]},\"id\":\"us10004bgk\"}],\"bbox\":[-153.4051,-54.2906,10,158.5463,59.6363,582.56]}";


    /**
     * Create a private constructor because no one should ever create a {@link QueryUtils} object.
     * This class is only meant to hold static variables and methods, which can be accessed
     * directly from the class name QueryUtils (and an object instance of QueryUtils is not needed).
     */
    private QueryUtils() {
    }

    /**
     * Return a list of {@link Earthquake} objects that has been built up from
     * parsing a JSON response.
     */
    public static ArrayList<Earthquake> extractEarthquakes() {

        // Create an empty ArrayList that we can start adding earthquakes to
        ArrayList<Earthquake> earthquakes = new ArrayList<>();

        // Try to parse the SAMPLE_JSON_RESPONSE. If there's a problem with the way the JSON
        // is formatted, a JSONException exception object will be thrown.
        // Catch the exception so the app doesn't crash, and print the error message to the logs.
        try {

            //  Parse the response given by the SAMPLE_JSON_RESPONSE string and
            // build up a list of Earthquake objects with the corresponding data.

                JSONObject BaseJsonResponse = new JSONObject(SAMPLE_JSON_RESPONSE);
                // Getting JSON Array Node
                JSONArray earthquakeArray = BaseJsonResponse.getJSONArray("Features");
                // looping through All Contacts
                for (int i = 0; i < earthquakeArray.length(); i++) {
                    JSONObject currentEarthquake = earthquakeArray.getJSONObject(i);
                    JSONObject properties= currentEarthquake.getJSONObject("properties");
                    String magnitude=properties.getString("mag");
                    String location=properties.getString("place");
                    String time=properties.getString("time");
                    Earthquake earthquake= new Earthquake(magnitude,location,time);
                    earthquakes.add(earthquake);



                }


            } catch (JSONException e) {
                // If an error is thrown when executing any of the above statements in the "try" block,
                // catch the exception here, so the app doesn't crash. Print a log message
                // with the message from the exception.
                Log.e("QueryUtils", "Problem parsing the earthquake JSON results", e);
            }

            // Return the list of earthquakes
            return earthquakes;
        }

    }

这是我的主要活动代码

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ListView;

import java.util.ArrayList;

public class EarthquakeActivity extends AppCompatActivity {

    public static final String LOG_TAG = EarthquakeActivity.class.getName();

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

        // Create a fake list of earthquake locations.
        ArrayList<Earthquake> earthquakes = QueryUtils.extractEarthquakes();

        // Find a reference to the {@link ListView} in the layout
        ListView earthquakeListView = (ListView) findViewById(R.id.list);

        // Create an {@link EarthquakeAdapter}, whose data source is a list of
        // {@link Earthquake}s. The adapter knows how to create list item views for each item
        // in the list.
        EarthquakeAdapter quakeAdapter = new EarthquakeAdapter(this,earthquakes);

        // Set the adapter on the {@link ListView}
        // so the list can be populated in the user interface
        earthquakeListView.setAdapter(quakeAdapter);
    }
}

以下是我制作的自定义类的代码。

public class Earthquake {


    //Magnitude of earthquake (e.g. 7.5,5.5,6.4 etc)
        private String mMagnitude;

        //Place of Earthquake (Kolkata, Delhi etc)
        private String mPlace;

        // Date Of the occurrence
        private String mDate;

        /*
        * Create a new Earthquake object.
        *
        * @param vName is the name of the Android version (e.g. Gingerbread)
        * @param vNumber is the corresponding Android version number (e.g. 2.3-2.7)
        * @param image is drawable reference ID that corresponds to the Android version
        * */
        public Earthquake(String eMagnitude, String ePlace, String eDate)
        {
            mMagnitude = eMagnitude;
            mPlace = ePlace;
            mDate = eDate;
        }

        /**
         * Get value of magnitude
         */
        public String getMagnitude() {
            return mMagnitude;
        }

        /**
         * Get the place of occurrence
         */
        public String getPlace() {
            return mPlace;
        }

        /**
         * Get the Date of occurrence
         */
        public String  getDate() {
            return mDate;
        }


    }

这是Custom数组适配器。

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.ArrayList;

/**
 * Created by Atanu on 25-06-2017.
 */

/*
* {@link EarthquakeAdapter} is an {@link ArrayAdapter} that can provide the layout for each list
* based on a data source, which is a list of {@link Earthquake} objects.
* */
public class EarthquakeAdapter extends ArrayAdapter<Earthquake> {

    private static final String LOG_TAG = EarthquakeAdapter.class.getSimpleName();

    /**
     * This is our own custom constructor (it doesn't mirror a superclass constructor).
     * The context is used to inflate the layout file, and the list is the data we want
     * to populate into the lists.
     *
     * @param context        The current context. Used to inflate the layout file.
     * @param earthquakes A List of Earthquake objects to display in a list
     */
    public EarthquakeAdapter(Activity context, ArrayList<Earthquake> earthquakes) {
        // Here, we initialize the ArrayAdapter's internal storage for the context and the list.
        // the second argument is used when the ArrayAdapter is populating a single TextView.
        // Because this is a custom adapter for three TextViews , the adapter is not
        // going to use this second argument, so it can be any value. Here, we used 0.
        super(context, 0, earthquakes);
    }

    /**
     * Provides a view for an AdapterView (ListView, GridView, etc.)
     *
     * @param position The position in the list of data that should be displayed in the
     *                 list item view.
     * @param convertView The recycled view to populate.
     * @param parent The parent ViewGroup that is used for inflation.
     * @return The View for the position in the AdapterView.
     */
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // Check if the existing view is being reused, otherwise inflate the view
        View listItemView = convertView;
        if(listItemView == null) {
            listItemView = LayoutInflater.from(getContext()).inflate(R.layout.list_item, parent, false);
        }

        // Get the {@link Earthquake} object located at this position in the list
        Earthquake currentEarthquake = getItem(position);

        // Find the TextView in the list_item.xml layout with the ID mag
        TextView magTextView = (TextView) listItemView.findViewById(R.id.mag);
        // Get the magnitude from the current Earthquake object and
        // set this text on the name TextView
        magTextView.setText(currentEarthquake.getMagnitude());

        // Find the TextView in the list_item.xml layout with the ID place
        TextView placeTextView = (TextView) listItemView.findViewById(R.id.place);
        // Get the place of occurrence from the current Earthquake object and
        // set this text on the number TextView
        placeTextView.setText(currentEarthquake.getPlace());

        // Find the Date of occurrence in the list_item.xml layout with the ID date
        TextView dateTextView = (TextView) listItemView.findViewById(R.id.date);
        // Get the Date of occurrence from the current Earthquake object and
        // set the date to TextView
        dateTextView.setText(currentEarthquake.getDate());

        // Return the whole list item layout (containing 3 TextViews )
        // so that it can be shown in the ListView
        return listItemView;
    }

}

请帮助我无法解决这个问题。提前谢谢。

Answer 1

您的Json字符串不正确

private static final String SAMPLE_JSON_RESPONSE="incorrect json"

请在在线验证器上验证[就像您在内联屏幕截图中看到的那样]并进行解析。

Answer 2

我只知道我犯的错误，JSON代码是正确的。我正在使用

JSONArray earthquakeArray = BaseJsonResponse.getJSONArray("Features");

insted of

JSONArray earthquakeArray = BaseJsonResponse.getJSONArray("features");

因为我的JSON脚本有一个名为“features”而不是“Features”的键。

Answer 3

你的json有问题。尝试通过两个虚拟变量来解析它。

PS：检查旁边的图像。 Json看起来不合适。Screenshot

Answer 4

只需从您从源代码复制的完整JSON字符串中删除'\'此斜杠。这将使您的JSON字符串有效，并且您的JSONObject调用将能够轻松地理解和解析您想要说的内容。使用像jsonlint.com

这样的json验证器

这是你的json没有\ slashes的第一个对象来证明你必须这样做：

{“type”：“FeatureCollection”，“metadata”：{“generated”：   1462295443000，“url”：   “http://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&starttime=2016-01-01&endtime=2016-01-31&minmag=6&limit=10”，         “title”：“USGS Earthquakes”，“status”：200，“api”：“1.5.2”，         “limit”：10，“offset”：1，“count”：10}，“features”：[{         “type”：“Feature”，“properties”：{“mag”：7.2，“place”：   “俄罗斯Yelizovo 88km N”，“时间”：1454124312220，“更新”：   1460674294040，“tz”：720，“url”：   “http://earthquake.usgs.gov/earthquakes/eventpage/us20004vvx”，             “详情”：   “http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=us20004vvx&format=geojson”，             “感觉”：2，“cdi”：3.4，“mmi”：5.82，“警告”：“绿色”，             “状态”：“已审核”，“海啸”：1，“sig”：798，“net”：   “us”，“code”：“20004vvx”，“ids”：   “，at00o1qxho，pt16030050，us20004vvx，gcmt20160130032510，”，“来源”：   “，at，pt，us，gcmt，”，“types”：   ”帽，dyfi，有限的故障，一般的链接，一般的文字，geoserve，冲击连杆，冲击文本，losspager，矩张量，附近的城市，产地，相数据，震动图，构造，总结， ”             “nst”：null，“dmin”：0.958，“rms”：1.19，“gap”：17，             “magType”：“mww”，“type”：“地震”，“标题”：“M 7.2 -   俄罗斯Yelizovo 88km N“}，”geometry“：{”type“：”Point“，             “coordinates”：[158.5463,53.9776,177]}，“id”：“us20004vvx”     }]

}

您可以复制此对象并在JSON验证器中验证或直接尝试解析它将起作用。

希望这有助于解决你的问题。

从网站Api中提取的Json代码解析数据时的空白屏幕输出

4 个答案: