我试图将json解析到应用程序中，但是当应用程序打开时，屏幕显示为空白。我试图找到错误，但什么都没有，使用每一个可能的代码，我认为问题是在获取json时..请帮助我................... ....................
main_activity.xml
<?xml version="1.0" encoding="utf-8"?>
<ListView
android:id="@+id/list"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="examle.android.com.networkexample.MainActivity">
</ListView>
list_item.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:padding="15dp"
xmlns:tools="http://schemas.android.com/tools"
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/login"
tools:text="USER_LOGIN"
android:textSize="18sp"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:paddingTop="2dp"
android:id="@+id/type"
tools:text="USER_TYPE"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
MainActivity.java
public class MainActivity extends AppCompatActivity {
private static String LOG_TAG = MainActivity.class.getSimpleName();
private static String JSON_URL = "https://api.github.com/users";
UserAdapter mAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView listView = (ListView)findViewById(R.id.list);
// Create a new adapter that takes an empty list of earthquakes as input
mAdapter = new UserAdapter(this, new ArrayList<User>());
listView.setAdapter(mAdapter);
UserAsync task = new UserAsync();
task.execute(JSON_URL);
}
private class UserAsync extends AsyncTask<String,Void,List<User>>{
@Override
protected List<User> doInBackground(String... urls) {
if(urls.length <1 || urls[0] == null){
return null;
}
List<User> result = null;
try {
result = QueryUtils.fetchJson(urls[0]);
} catch (JSONException e) {
Log.e(LOG_TAG,"Error in fetching json",e);
}
return result;
}
@Override
protected void onPostExecute(List<User> users) {
// Clear the adapter of previous earthquake data
mAdapter.clear();
// If there is a valid list of {@link user}s, then add them to the adapter's
// data set. This will trigger the ListView to update.
if(users != null && users.isEmpty()){
mAdapter.addAll(users);
}
}
}
}
QueryUtils.java
public class QueryUtils {
private static final String LOG_TAG = QueryUtils.class.getSimpleName();
public QueryUtils() {
}
/**
* Query the github dataset and return a list of {users} objects.
*/
public static List<User> fetchJson(String requestUrl) throws JSONException {
//create URL object
URL url = createUrl(requestUrl);
//perform http request to the URL and receive a json
String jsonResponse = null;
try {
jsonResponse = makeHttpRequest(url);
} catch (IOException e) {
Log.e(LOG_TAG,"problem in making http request",e);
}
// Extract relevant fields from the JSON response and create a list of {@link Users}
List<User> users = extractFromJson(jsonResponse);
//return list of {@link Users}
return users;
}
/**
* Returns new URL object from the given string URL.
*/
private static URL createUrl(String stringUrl){
URL url = null;
try {
url = new URL(stringUrl);
} catch (MalformedURLException e) {
Log.e(LOG_TAG,"Error in creating url",e);
}
return url;
}
/**
* Make an HTTP request to the given URL and return a String as the response.
*/
private static String makeHttpRequest(URL url) throws IOException{
String jsonResponse = "";
//If url is null return early
if(url == null){
return jsonResponse;
}
HttpURLConnection urlConnection = null;
InputStream inputStream = null;
try{
urlConnection = (HttpURLConnection)url.openConnection();
urlConnection.setReadTimeout(10000);
urlConnection.setConnectTimeout(15000);
urlConnection.setRequestMethod("GET");
if(urlConnection.getResponseCode() == 200){
inputStream = urlConnection.getInputStream();
jsonResponse = readFromStream(inputStream);
}else {
Log.e(LOG_TAG,"Error response code: " + urlConnection.getResponseCode());
}
}catch (IOException e){
Log.e(LOG_TAG,"Problem in retrieving the json response",e);
}finally {
if (urlConnection != null){
urlConnection.disconnect();
}
if (inputStream != null){
inputStream.close();
}
}
return jsonResponse;
}
/**
* Convert the {@link InputStream} into a String which contains the
* whole JSON response from the server.
*/
private static String readFromStream(InputStream inputStream) throws IOException {
StringBuilder output = new StringBuilder();
if (inputStream != null){
InputStreamReader inputStreamReader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
BufferedReader reader = new BufferedReader(inputStreamReader);
String line = reader.readLine();
while (line != null){
output.append(line);
line = reader.readLine();
}
}
return output.toString();
}
private static List<User> extractFromJson(String user) throws JSONException {
// If the JSON string is empty or null, then return early.
if (TextUtils.isEmpty(user)) {
return null;
}
// Create an empty ArrayList that we can start adding earthquakes to
List<User> users = new ArrayList<>();
try{
JSONArray array = new JSONArray(user);
for (int i = 0; i<array.length(); i++){
JSONObject jsonObject = array.getJSONObject(i);
String login = jsonObject.getString("login");
String type = jsonObject.getString("type");
User user1 = new User(login,type);
users.add(user1);
}
}catch (JSONException e){
Log.e(LOG_TAG,"Problem in parsing user",e);
}
return users;
}
}
UserAdapter.java
public class UserAdapter extends ArrayAdapter<User>{
public UserAdapter(@NonNull Context context, @NonNull List<User> objects) {
super(context, 0, objects);
}
@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
View listView = convertView;
if (listView == null){
listView = LayoutInflater.from(getContext()).inflate(R.layout.list_item,parent,false);
}
User currentUser = getItem(position);
TextView login = (TextView)listView.findViewById(R.id.login);
login.setText(currentUser.getUser_login());
TextView type = (TextView) listView.findViewById(R.id.type);
type.setText(currentUser.getType());
return listView;
}
}
User.java
public class User {
private String user_login;
private String type;
public User(String user_login, String type) {
this.user_login = user_login;
this.type = type;
}
public String getUser_login() {
return user_login;
}
public String getType() {
return type;
}
}
答案 0 :(得分：0)
您可能需要修改onPostExecute方法中的If语句。仅当用户不为null且用户为空时才更新适配器。您应该在非空的情况下更新适配器
if(users != null && users.isEmpty()){
mAdapter.addAll(users);
}
到
if(users != null && !users.isEmpty()){
mAdapter.addAll(users);
}
答案 1 :(得分：0)
修改users.isEmpty()。条件永远不会满足。你必须改变它，你也必须拨打mAdapter.notifyDataSetChanged();
if(users != null && !users.isEmpty()){
mAdapter.addAll(users);
mAdapter.notifyDataSetChanged();
}
答案 2 :(得分：0)
从头开始，适配器使用空数据初始化。完成异步任务后，您需要通过通知来更新UI。
@Override
protected void onPostExecute(List<User> users) {
// Clear the adapter of previous earthquake data
mAdapter.clear();
// If there is a valid list of {@link user}s, then add them to the adapter's
// data set. This will trigger the ListView to update.
if(users != null && users.isEmpty()){
mAdapter.addAll(users);
// After adding user to the adapter, Notify adapter for UI update
mAdapter.notifyDataSetChanged();
}
}
这将使用用户数据更新UI。
答案 3 :(得分：0)
代码适用于此更改
您可能需要修改onPostExecute方法中的If语句。仅当用户不为null且用户为空时才更新适配器。您应该在非空的情况下更新适配器
if(users != null && users.isEmpty()){
mAdapter.addAll(users);
}
To
if(users != null && !users.isEmpty()){
mAdapter.addAll(users);
}