我是Java和Android开发的新手。
坚持在Android中实现“刷新以刷新” 。我正在尝试访问其他类中的方法。我将突出显示android studio在blockquote中给出的错误。非常感谢您的帮助。
MainActivity.java
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.widget.SwipeRefreshLayout;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
public class MainActivity extends AppCompatActivity{
private String TAG = MainActivity.class.getSimpleName();
private SwipeRefreshLayout swipeRefreshLayout;
private ProgressDialog pDialog;
private ListView lv;
// URL to get contacts JSON
private static String url = "http://hooman.com/hoo.php";
ArrayList<HashMap<String, String>> contactList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
contactList = new ArrayList<>();
swipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swiperefresh);
lv = (ListView) findViewById(R.id.list);
swipeRefreshLayout.setOnRefreshListener(this); swipeRefreshLayout.post(new Runnable() { @Override public void run() { swipeRefreshLayout.setRefreshing(true); doInBackground(); } } ); new GetContacts().execute(); } @Override public void onRefresh() { doInBackground(); }
/**
* Async task class to get json by making HTTP call
*/
private class GetContacts extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Showing progress dialog
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(Void... arg0) {
HttpHandler sh = new HttpHandler();
swipeRefreshLayout.setRefreshing(true);
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(url);
Log.e(TAG, "Response from url: " + jsonStr);
if (jsonStr != null) {
try {
JSONArray contacts = new JSONArray(jsonStr);
// looping through All Contacts
for (int i = 0; i < contacts.length(); i++) {
JSONObject c = contacts.getJSONObject(0);
String kw = c.getString("kw");
String kva = c.getString("kva");
String pf = c.getString("pf");
// tmp hash map for single contact
HashMap<String, String> contact = new HashMap<>();
// adding each child node to HashMap key => value
contact.put("kw", kw);
contact.put("kva", kva);
contact.put("pf", pf);
// adding contact to contact list
contactList.add(contact);
// stopping swipe refresh
swipeRefreshLayout.setRefreshing(false);
}
} catch (final JSONException e) {
Log.e(TAG, "Json parsing error: " + e.getMessage());
Log.e("JSON Parser", "Error parsing data " + e.toString());
runOnUiThread(new Runnable() {
@Override
public void run() {
Toast.makeText(getApplicationContext(),
"Json parsing error: " + e.getMessage(),
Toast.LENGTH_LONG)
.show();
}
});
}
} else {
Log.e(TAG, "Couldn't get json from server.");
runOnUiThread(new Runnable() {
@Override
public void run() {
Toast.makeText(getApplicationContext(),
"Couldn't get json from server. Check LogCat for possible errors!",
Toast.LENGTH_LONG)
.show();
// stopping swipe refresh
swipeRefreshLayout.setRefreshing(false);
}
});
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
MainActivity.this, contactList,
R.layout.list_item, new String[]{"kw", "kva",
"pf"}, new int[]{R.id.kw,
R.id.kva, R.id.pf});
lv.setAdapter(adapter);
}
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.SwipeRefreshLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/swiperefresh"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<ListView
android:id="@+id/list"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</android.support.v4.widget.SwipeRefreshLayout>
list_item.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:padding="10dp">
<TextView
android:id="@+id/kw"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:paddingBottom="2dip"
android:paddingTop="6dip"
android:textColor="@color/colorPrimaryDark"
android:textSize="16sp"
android:textStyle="bold" />
<TextView
android:id="@+id/kva"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:paddingBottom="2dip"
android:textColor="@color/colorAccent" />
<TextView
android:id="@+id/pf"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="#5d5d5d"
android:textStyle="bold" />
</LinearLayout>
谢谢。
答案 0 :(得分:1)
首先,您具有循环依赖关系。 AsyncTask无法引用“活动”中的swipeRefreshLayout
视图,并且活动将需要一个任务实例才能调用task.doInBackground()
(您应该绝对不要这样做”)。只需要使用execute()
,很少使用execute().get()
您可以做的是在活动中覆盖postExecute函数
swipeRefreshLayout.post(new Runnable() {
@Override
public void run() {
swipeRefreshLayout.setRefreshing(true);
// Showing progress dialog
final ProgressDialog pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
contactList.clear();
new GetContacts() {
@Override
protected void onPostExecute(Void result) {
// stopping swipe refresh
swipeRefreshLayout.setRefreshing(false);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
ListAdapter adapter = new SimpleAdapter(
MainActivity.this, contactList, R.layout.list_item,
new String[]{"kw", "kva", "pf"},
new int[]{R.id.kw,R.id.kva, R.id.pf});
lv.setAdapter(adapter);
}
}.execute();
}
}
);
答案 1 :(得分:0)
首先,不要从doInBackground()方法调用UI视图。
您可以通过onPreExcute()方法或onPostExecute方法调用它们。
但是由于AsyncTask在其他文件中,因此您也不能直接调用它们。
由于您要在刷新SwipeRefreshLayout时执行AsyncTask代码。
有2种方法:
1st:使AsyncTask类成为调用活动的内部类。 (仅在您仅要在此活动中使用此Asynctask时有用。
2nd:在AsyncTask How to get the result of OnPostExecute() to main activity because AsyncTask is a separate class?
中实现回调3:使用排球/翻新(库)。 (由于您仅调用API并获取JSON数据,因此默认情况下,它们使用“主线程以外的其他线程”,并且也内置了JSON支持。