以前我使用过ArrayAdapter和列表视图，所以我做了这段代码来更新UI。
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);
// After adding user to the adapter, Notify adapter for UI update
mAdapter.notifyDataSetChanged();
}
}
}
现在我已尝试RecyclerView和CardView来获取数据，但上述代码不适用于recyclerview ..
我想知道如何为回收商视图实施doInBackground和onPostExecute
activity_main.xml中
<android.support.constraint.ConstraintLayout 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.recyclerviewnetwork.MainActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerview"
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.v7.widget.RecyclerView>
</android.support.constraint.ConstraintLayout>
items.xml
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/card"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:elevation="8dp"
app:cardCornerRadius="5dp"
android:layout_marginTop="5dp"
android:layout_marginLeft="5dp"
android:layout_marginRight="5dp"
android:padding="25dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal">
<ImageView
android:id="@+id/avatar"
android:layout_width="108dp"
android:layout_height="108dp"
android:padding="15dp"
tools:src="@mipmap/ic_launcher" />
<LinearLayout
android:paddingRight="15dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView
android:id="@+id/login"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="15dp"
tools:text="LOGIN_USER" />
<TextView
android:id="@+id/type"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="3dp"
tools:text="USER_TYPE" />
</LinearLayout>
</LinearLayout>
</android.support.v7.widget.CardView>
Main_activity.java
public class MainActivity extends AppCompatActivity {
RecyclerView recyclerView;
UserAdapter mAdapter;
RecyclerView.LayoutManager layoutManager;
private static final String JSON_URL = "https://api.github.com/users";
private static final String LOG_TAG = MainActivity.class.getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView) findViewById(R.id.recyclerview);
mAdapter = new UserAdapter(new ArrayList<User>(),this);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setAdapter(mAdapter);
UserAsyncTask task = new UserAsyncTask();
task.execute(JSON_URL);
}
public class UserAsyncTask 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) {
super.onPostExecute(users);
}
}
}
QueryUtils.java
public class QueryUtils {
private static final String LOG_TAG = QueryUtils.class.getSimpleName();
public QueryUtils() {
}
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);
}
List<User> users = extractJson(jsonResponse);
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 == 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 Json Response",e);
}finally {
if (urlConnection != null){
urlConnection.disconnect();
}
if (inputStream !=null){
inputStream.close();
}
}
return jsonResponse;
}
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> extractJson(String json) throws JSONException{
// If the JSON string is empty or null, then return early.
if(TextUtils.isEmpty(json)){
return null;
}
//create an empty arrylist
List<User> users = new ArrayList<>();
try{
JSONArray jsonArray = new JSONArray();
for (int i = 0; i<jsonArray.length(); i++){
JSONObject jsonObject = jsonArray.getJSONObject(i);
String login = jsonObject.getString("login");
String type = jsonObject.getString("type");
String avatar = jsonObject.getString("avatar_url");
User user = new User(login,type,avatar);
users.add(user);
}
}catch (JSONException e){
Log.e(LOG_TAG,"Error in parsing the JSON",e);
}
return users;
}
}
UserAdapter.java
public class UserAdapter extends RecyclerView.Adapter<UserAdapter.UserViewHolder> {
ArrayList<User> users = new ArrayList<>();
Context context;
public UserAdapter(ArrayList<User> users, Context context) {
this.users = users;
this.context = context;
}
@Override
public UserViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.items,parent,false);
return new UserViewHolder(view);
}
@Override
public void onBindViewHolder(UserViewHolder holder, int position) {
holder.login.setText(users.get(position).getUser_login());
holder.type.setText(users.get(position).getType());
Picasso.with(context).load(String.valueOf(users.get(position))).into(holder.avatar);
}
@Override
public int getItemCount() {
return users.size();
}
public class UserViewHolder extends RecyclerView.ViewHolder {
TextView login;
TextView type;
ImageView avatar;
public UserViewHolder(View itemView) {
super(itemView);
login = (TextView)itemView.findViewById(R.id.login);
type = (TextView)itemView.findViewById(R.id.type);
avatar = (ImageView)itemView.findViewById(R.id.avatar);
}
}
}
User.java
public class User {
private String user_login;
private String type;
private String url;
public User(String user_login, String type, String url) {
this.user_login = user_login;
this.type = type;
this.url = url;
}
public String getUser_login() {
return user_login;
}
public String getType() {
return type;
}
public String getUrl() {
return url;
}
}
答案 0 :(得分：0)
更新代码：
在您的活动中：
public class MainActivity extends AppCompatActivity {
RecyclerView recyclerView;
UserAdapter mAdapter;
RecyclerView.LayoutManager layoutManager;
private static final String JSON_URL = "https://api.github.com/users";
private static final String LOG_TAG = MainActivity.class.getSimpleName();
public ArrayList users = new ArrayList＆lt;＆gt;（）;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView) findViewById(R.id.recyclerview);
mAdapter = new UserAdapter(users,this);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setAdapter(mAdapter);
UserAsyncTask task = new UserAsyncTask();
task.execute(JSON_URL);
}
在您的异步任务中：
public class UserAsyncTask extends AsyncTask<String, Void, List<User>>{
@Override
protected List<User> doInBackground(String... urls) {
if(urls.length < 1 || urls[0] == null ){
return null;
}
try{
users = 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) {
super.onPostExecute(users);
if(users != null && !users.isEmpty()){
mAdapter.notifyDataSetChanged();
}
}
}
或者使用您用于Listview的相同onPostExecute方法，并在recyclerview适配器中创建mAdapter.addAll(users);相同的方法。
答案 1 :(得分：0)
在适配器中创建以下方法：
清理数据：
public void clear() {
int itemCount = getItemCount();
users.clear();
// notify your adapter that the data has been changed. You can also use notifyDataSetChanged() if you don't have an animation
if (itemCount > 0)
notifyItemRangeRemoved(0, itemCount);
}
将项目添加到适配器：
public void addAll(List<User> addUsers) {
for (User user : addUsers) {
users.add(l_user);
// notify your adapter that the data has been changed. You can also use notifyDataSetChanged() if you don't have an animation.
// If you use notifyDataSetChanged() you can call it on the outside of this loop just once
notifyItemInserted(users.size());
}
}
现在，您可以在AsyncTask的onPostExecute()中调用这些方法：
@Override
protected void onPostExecute(List<User> users) {
// clear the previous data
mAdapter.clear();
// add the new data
if(users != null)
mAdapter.addAll(users);
}