我正在尝试使用监护人API进行项目，该API从JSON获取数据，并在ListView中将所有新闻显示在屏幕上，我已经尝试了所有可能的方法，并且还记录了信息以验证代码流，并且所有工作正常，没有错误和崩溃，唯一的问题是它没有在屏幕上显示数据，屏幕为空白，请帮助我
此处输出： Blank Screen
这是AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.hannan.newsfeed">
<uses-permission android:name="android.permission.INTERNET"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
这是MainActivity.java
package com.example.hannan.newsfeed;
import android.content.Intent;
import android.os.AsyncTask;
import android.support.v4.content.AsyncTaskLoader;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private static final String LOG_TAG = MainActivity.class.getSimpleName();
private static final String GAURDIAN_URL = "https://content.guardianapis.com/search?api-key=d7262a1a-2583-4342-9b57-85ed0f621416";
private NewsAdapter mAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView listView = findViewById(R.id.list);
mAdapter = new NewsAdapter(this, new ArrayList<NewsModel>());
listView.setAdapter(mAdapter);
NewsAsyncTask task = new NewsAsyncTask();
task.execute(GAURDIAN_URL);
}
private class NewsAsyncTask extends AsyncTask<String, Void, List<NewsModel>> {
@Override
protected List<NewsModel> doInBackground(String... urls) {
Log.i(LOG_TAG, "TEST: In doInBackground");
if (urls.length < 1 || urls[0] == null) {
Log.i(LOG_TAG, "TEST: No urls available");
return null;
}
List<NewsModel> result = QueryUtils.fetch_data(urls[0]);
Log.i(LOG_TAG, "TEST: In fetch_data() method of QueryUtils class");
return result;
}
@Override
protected void onPostExecute(List<NewsModel> newsModels) {
Log.i(LOG_TAG, "TEST: Completed doInBackground() Method");
mAdapter.clear();
Log.i(LOG_TAG, "TEST: Adapter Cleared");
if (newsModels != null && !newsModels.isEmpty()) {
Log.i(LOG_TAG, "TEST:Data added to Adapter");
mAdapter.addAll();
} else {
Log.i(LOG_TAG, "TEST: No data in Model");
}
}
}
}
这是NewsAdapter.java
package com.example.hannan.newsfeed;
import android.app.Activity;
import android.content.Context;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;
public class NewsAdapter extends ArrayAdapter {
private static final String LOG_TAG = MainActivity.class.getSimpleName();
public NewsAdapter(@NonNull Context context, ArrayList<NewsModel> newslist) {
super(context, 0, newslist);
}
@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
if (convertView == null) {
LayoutInflater.from(getContext()).inflate(R.layout.list_news, parent, false);
}
NewsModel currentNews = (NewsModel) getItem(position);
TextView news_title = convertView.findViewById(R.id.news_title);
TextView news_section = convertView.findViewById(R.id.news_section);
TextView news_date = convertView.findViewById(R.id.news_date);
news_title.setText(currentNews.getmNewsTitle());
news_section.setText(currentNews.getmNewsSection());
news_date.setText(currentNews.getmNewsDate());
return convertView;
}
}
这是NewsModel.java
package com.example.hannan.newsfeed;
public class NewsModel {
private String mNewsTitle;
private String mNewsSection;
private String mNewsDate;
private String mNewsUrl;
NewsModel(String news_title,String news_section, String news_date, String news_url){
mNewsTitle = news_title;
mNewsSection = news_section;
mNewsDate = news_date;
mNewsUrl = news_url;
}
public String getmNewsTitle() {
return mNewsTitle;
}
public String getmNewsSection() {
return mNewsSection;
}
public String getmNewsDate() {
return mNewsDate;
}
public String getmNewsUrl() {
return mNewsUrl;
}
}
这是QueryUtils.java
package com.example.hannan.newsfeed;
import android.text.TextUtils;
import android.util.Log;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;
import javax.net.ssl.HttpsURLConnection;
public class QueryUtils {
private static final String LOG_TAG = QueryUtils.class.getSimpleName();
private QueryUtils() {
}
public static ArrayList<NewsModel> fetch_data(String requestedUrl) {
URL url = createURL(requestedUrl);
Log.i(LOG_TAG, "TEST: URL Requested");
String jsonResponse = null;
try {
jsonResponse = makeHttpRequest(url);
Log.i(LOG_TAG, "TEST: JSON Response created");
} catch (IOException e) {
e.printStackTrace();
}
ArrayList<NewsModel> listnews = extractResponseFromJson(jsonResponse);
return listnews;
}
private static URL createURL(String stringUrl) {
URL url = null;
try {
url = new URL(stringUrl);
Log.i(LOG_TAG, "TEST: URL Created " + url);
} catch (MalformedURLException e) {
Log.e(LOG_TAG, "TEST:Problem Building URL..", e);
}
return url;
}
private static String makeHttpRequest(URL url) throws IOException {
String jsonResponse = "";
if (url == null) {
return jsonResponse;
}
HttpsURLConnection urlConnection = null;
InputStream is = null;
try {
urlConnection = (HttpsURLConnection) url.openConnection();
urlConnection.setReadTimeout(10000);
urlConnection.setConnectTimeout(15000);
urlConnection.setRequestMethod("GET");
urlConnection.connect();
if (urlConnection.getResponseCode() == 200) {
is = urlConnection.getInputStream();
jsonResponse = readFromStream(is);
Log.i(LOG_TAG, "TEST: Connected with HTTP");
} else {
Log.e(LOG_TAG, "TEST:Error Response Code:" + urlConnection.getResponseCode());
}
} catch (IOException e) {
Log.e(LOG_TAG, "TEST:Problem retrieving Data", e);
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (is != null) {
is.close();
}
}
return jsonResponse;
}
private static String readFromStream(InputStream inputStream) throws IOException {
StringBuilder stringBuilder = new StringBuilder();
Log.i(LOG_TAG, "TEST: String builder created");
if (inputStream != null) {
InputStreamReader inputStreamReader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
BufferedReader reader = new BufferedReader(inputStreamReader);
String line = reader.readLine();
while (line != null) {
stringBuilder.append(line);
line = reader.readLine();
}
}
Log.i(LOG_TAG, "TEST: returning String builder");
return stringBuilder.toString();
}
private static ArrayList<NewsModel> extractResponseFromJson(String newsJson) {
Log.i(LOG_TAG, "TEST: In extractResponseFromJson() method..");
if (TextUtils.isEmpty(newsJson)) {
Log.i(LOG_TAG, "TEST: newsJson is empty");
return null;
}
ArrayList<NewsModel> newslist = new ArrayList<>();
Log.i(LOG_TAG, "TEST: ArrayList created");
try {
JSONObject baseObject = new JSONObject(newsJson);
Log.i(LOG_TAG, "TEST: JSON object created");
JSONObject responseArray = baseObject.getJSONObject("response");
Log.i(LOG_TAG, "JSON object fetched" + responseArray);
JSONArray resultArray = responseArray.getJSONArray("results");
for (int i = 0; i < resultArray.length(); i++) {
Log.i(LOG_TAG, "TEST: In for loop");
JSONObject currentNews = resultArray.getJSONObject(i);
String title = currentNews.getString("webTitle");
String section_name = currentNews.getString("sectionName");
String published_date = currentNews.getString("webPublicationDate");
String url = currentNews.getString("webUrl");
NewsModel news = new NewsModel(title, section_name, published_date, url);
newslist.add(news);
Log.i(LOG_TAG, "TEST: JSON data Added to Model");
}
} catch (JSONException e) {
e.printStackTrace();
Log.e(LOG_TAG, "Error fetching Data from JSON");
}
return newslist;
}
}
这是main_activity.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<ListView
android:id="@+id/list"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</RelativeLayout>
这是list_news.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="10dp"
xmlns:tools="http://schemas.android.com/tools">
<TextView
android:id="@+id/news_title"
android:layout_width="match_parent"
android:padding="8dp"
android:textSize="20sp"
android:layout_height="wrap_content"
tools:text="News Title"/>
<TextView
android:id="@+id/news_section"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/news_title"
tools:text="News Section"
android:textSize="14sp"
android:layout_alignParentLeft="true"
android:padding="8dp"/>
<TextView
android:id="@+id/news_date"
android:textSize="12sp"
android:padding="8dp"
tools:text="News Date"
android:layout_below="@id/news_title"
android:layout_alignParentRight="true"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>