我正在尝试从另一个类执行asynctask并更新listview和toast。
但是我做不到。它的崩溃位置：
progressDialog = new ProgressDialog(context);
我非常感谢您的帮助。
提取类
public class fetch extends AsyncTask<Void, Void, JSONObject> {
Context context;
Activity activity ;
ListView list;
LazyAdapter adapter;
ArrayList<HashMap<String, String>> songsList;
ProgressDialog progressDialog ;
@Override
protected JSONObject doInBackground(Void... params) {
String ResponseBody = null;
try {
String user = "1";
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://www.example.com/example.php");
// Add your data
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
nameValuePairs.add(new BasicNameValuePair("user",user) );
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
// Execute HTTP Post Request
HttpResponse response = httpclient.execute(httppost);
BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent(), "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line = "0";
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
reader.close();
String result = sb.toString();
// parsing data
return new JSONObject(result);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
runOnUiThread(new Runnable() {
@Override
public void run() {
progressDialog = new ProgressDialog(MainActivity.this);
progressDialog.setMessage("loading...");
progressDialog.setCanceledOnTouchOutside(false);
progressDialog.show();
}
});
}
@Override
protected void onPostExecute(JSONObject result) {
super.onPostExecute(result);
if (result != null) {
JSONArray arr = result.getJSONArray("Array");
for (int i = 0; i <arr.Length(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
Element e = (Element) nl.item(i);
// adding each child node to HashMap key => value
map.put(KEY_ID, parser.getValue(e, KEY_ID));
map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
map.put(KEY_ARTIST, parser.getValue(e, KEY_ARTIST));
map.put(KEY_DURATION, parser.getValue(e, KEY_DURATION));
map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));
// adding HashList to ArrayList
songsList.add(map);
}
}
list=(ListView)findViewById(R.id.ListView);
// Getting adapter by passing xml data ArrayList
adapter=new LazyAdapter(MainActivity.this, songsList);
list.setCacheColorHint(0);
list.setScrollingCacheEnabled(false);
list.setAdapter(adapter);
// Click event for single list row
list.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
Toast.makeText(getBaseContext(), position+" "+id, 5).show();
}
});
} else {
// error occured
}
runOnUiThread(new Runnable() {
@Override
public void run() {
progressDialog.dismiss();
Toast.makeText(getBaseContext(), "done", 5).show();
}
});
}
public fetch(Context context) {
activity = (context instanceof Activity) ? (Activity) context : null;
this.context = context;
progressDialog = new ProgressDialog(context);
}
}
LazyAdapter.java
package com.example.androidhive;
import java.util.ArrayList;
import java.util.HashMap;
import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
public class LazyAdapter extends BaseAdapter {
private Activity activity;
private ArrayList<HashMap<String, String>> data;
private static LayoutInflater inflater=null;
public ImageLoader imageLoader;
public LazyAdapter(Activity a, ArrayList<HashMap<String, String>> d) {
activity = a;
data=d;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader=new ImageLoader(activity.getApplicationContext());
}
public int getCount() {
return data.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
View vi=convertView;
if(convertView==null)
vi = inflater.inflate(R.layout.list_row, null);
TextView title = (TextView)vi.findViewById(R.id.title); // title
TextView artist = (TextView)vi.findViewById(R.id.artist); // artist name
TextView duration = (TextView)vi.findViewById(R.id.duration); // duration
ImageView thumb_image=(ImageView)vi.findViewById(R.id.list_image); // thumb image
HashMap<String, String> song = new HashMap<String, String>();
song = data.get(position);
// Setting all values in listview
title.setText(song.get(CustomizedListView.KEY_TITLE));
artist.setText(song.get(CustomizedListView.KEY_ARTIST));
duration.setText(song.get(CustomizedListView.KEY_DURATION));
imageLoader.DisplayImage(song.get(CustomizedListView.KEY_THUMB_URL), thumb_image);
return vi;
}
}
主要活动
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
Button btn=(Button)findViewById(R.id.button1);
btn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
RelativeLayout rootView = (RelativeLayout)findViewById(R.id.rootLayout);
PopoverView popoverView = new PopoverView(PopoverViewActivity.this, R.layout.popover_showed_view);
popoverView.setContentSizeForViewInPopover(new Point(400, 480));
popoverView.setDelegate(PopoverViewActivity.this);
popoverView.showPopoverFromRectInViewGroup(rootView, PopoverView.getFrameForView(v), PopoverView.PopoverArrowDirectionUp, true);
songsList = new ArrayList<HashMap<String, String>>();
fetch load=new fetch(getBaseContext());
load.execute();
}
});
}
最佳答案
这段代码有问题
progressDialog = new ProgressDialog(context);
需要当前显示的活动的上下文。看来您正在向它传递非显示活动上下文（在您的情况下为null）。它需要显示活动上下文才能显示进度条。
在调用fetch时，您在主要活动中将其传递为null。你应该改变
fetch(null);
至
fetch(MainActivity.this);
希望这可以帮助。