我正在开发一个应该从Web服务获得JSON响应的应用程序并编写 listview 中的每个元素，我已经读过我应该使用 AsyncTask 获得HTTP响应，我做了它，我可以从Web服务检索数据并在 TextViews 中显示它们。但是当我尝试在列表视图中显示元素时，它不会显示任何内容，并在logcat中给我以下消息：06-05 19:44:27.418: I/Choreographer(20731): Skipped 60 frames! The application may be doing too much work on its main thread.
这是我的主要代码：
public class MainActivity extends Activity {
private static JsonObject response = new JsonObject();
private ArrayList<SearchResults> results = new ArrayList<SearchResults>();
private SearchResults sr1 = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new LoginAction().execute("");
ArrayList<SearchResults> searchResults = results;
final ListView lv1 = (ListView) findViewById(R.id.ListView01);
lv1.setAdapter(new MyCustomBaseAdapter(this, searchResults));
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
private class LoginAction extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String... params) {
Map<String, String> callArgs = new HashMap<String, String>(1);
callArgs.put("suuid", "dtr0bdQGcqwSh3QO7fVwgVfBNWog6mvEbAyljlLX9E642Yfmur");
try {
response = EventPulseCloud.call("ListEvents", callArgs);
} catch (HttpClientException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JsonException e) {
e.printStackTrace();
}
return response.get("Type").toString();
}
protected void onPostExecute(String result) {
if(result.equals("success")) {
JsonArray records = null;
try {
records = response.getObject ("Data").getArray ("Records");
} catch (JsonException e) {
e.printStackTrace();
}
for(int i = 0; i < records.count(); i++) {
JsonObject record = (JsonObject) records.get(i);
sr1 = new SearchResults();
sr1.setAddress(record.get("address").toString());
results.add(sr1);
}
}
}
}
}
我的列表适配器：
public class MyCustomBaseAdapter extends BaseAdapter {
private static ArrayList<SearchResults> searchArrayList;
private LayoutInflater mInflater;
public MyCustomBaseAdapter(Context context, ArrayList<SearchResults> results) {
searchArrayList = results;
mInflater = LayoutInflater.from(context);
}
public int getCount() {
return searchArrayList.size();
}
public Object getItem(int position) {
return searchArrayList.get(position);
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.custom_row_view, null);
holder = new ViewHolder();
holder.txtAddress = (TextView) convertView.findViewById(R.id.address);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.txtAddress.setText(searchArrayList.get(position).getAddress());
return convertView;
}
static class ViewHolder {
TextView txtAddress;
}
}
最后，SearchResults.java：
public class SearchResults {
private String address = "";
public void setAddress(String address) {
this.address = address;
}
public String getAddress() {
return address;
}
}
那么，我做错了什么？你对此有所了解吗？
谢谢。
答案 0 :(得分：21)
onPostExecute()发生在主UI线程上。看起来你仍然在该方法中做了相当多的工作，应该在UI线程上完成，即处理响应，迭代JSON对象等。在doInBackground()中执行此操作并返回一个列表结果，所以onPostExecute唯一需要做的就是将新项目传递给列表适配器。
此外，不要使用与适配器保持的ArrayList相同的ArrayList。如果由于某种原因，适配器在没有调用notifyDataSetChanged()的情况下发现数据已更改，则可能会崩溃（或至少显示奇怪的行为）。在AsyncTask中创建一个新的ArrayList，然后将其放入适配器并从onPostExecute调用它：
public void setListItems(ArrayList<SearchResult> newList) {
searchArrayList = newList;
notifyDataSetChanged();
}
答案 1 :(得分：10)
private class LoginAction extends AsyncTaskList<String, Void, ArrayList<SearchResult>> {
@Override
protected ArrayList<SearchResult> doInBackground(String... params) {
List<SearchResults> resultList = new ArrayList<SearchResults>();
Map<String, String> callArgs = new HashMap<String, String>(1);
callArgs.put("suuid", "dtr0bdQGcqwSh3QO7fVwgVfBNWog6mvEbAyljlLX9E642Yfmur");
try {
response = EventPulseCloud.call("ListEvents", callArgs);
} catch (HttpClientException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JsonException e) {
e.printStackTrace();
}
//See here I am running the loop in the background so its not on the main thread, then passing the list off to the onpostexecute that way all the main thread does is set the adapter list and notify it of the data update and the list should be updated on the screen
if( response.get("Type").toString().equals("success")) {
JsonArray records = null;
try {
records = response.getObject ("Data").getArray ("Records");
} catch (JsonException e) {
e.printStackTrace();
}
for(int i = 0; i < records.count(); i++) {
JsonObject record = (JsonObject) records.get(i);
sr1 = new SearchResults();
sr1.setAddress(record.get("address").toString());
resultList.add(sr1);
}
}
return resultList;
}
protected void onPostExecute(ArrayList<SearchResult> resultList) {
setListItems(resultList);
}
}
}
在oncreate之前添加此行以及所有其他全局var
//here you want to create an adapter var with your base adapter so you can set it the updated list later when you have populated data from the internet
ArrayList<SearchResults> searchResults = new ArrayList<SearchResults>();
MyCustomBaseAdapter adapter = new MyCustomBaseAdapter(this, searchResults)
将其粘贴到您的oncreate方法上（替换它）
//here is just the code to update your main method to reflect all the changes I made
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new LoginAction().execute("");
final ListView lv1 = (ListView) findViewById(R.id.ListView01);
lv1.setAdapter(adapter);
}
并将此方法添加到适配器（MyCustomnBaseAdapter类）代码
public void setListItems(ArrayList<SearchResult> newList) {
searchArrayList = newList;
notifyDataSetChanged();
}