Android 如何使用异步任务返回对象?
我正在尝试从异步任务解析后返回tweet列表。。。。 但我不会从任务中取回arraylist。 有人能提出解决办法吗Android 如何使用异步任务返回对象?,android,multithreading,Android,Multithreading,我正在尝试从异步任务解析后返回tweet列表。。。。 但我不会从任务中取回arraylist。 有人能提出解决办法吗 public class Main extends ListActivity { String MY_APP_TAG = "com.list"; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstance
public class Main extends ListActivity {
String MY_APP_TAG = "com.list";
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ArrayList listItems = new ArrayList();
new myAsyncTask().execute(listItems);
setListAdapter(new ArrayAdapter(this, R.layout.tweet, R.id.tweet,listItems));
ListView lv = getListView();
lv.setTextFilterEnabled(true);
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
// When clicked, show a Toaster
Toast.makeText(getApplicationContext(), ((TextView) view).getText(), Toast.LENGTH_SHORT).show();
}
});
}
private class myAsyncTask extends AsyncTask<ArrayList<Object>, Void, Void>
{
ArrayList<Object> listItems;
ProgressDialog dialog;
@Override
protected void onPreExecute() {
dialog = ProgressDialog.show(Main.this, "", "Loading....");
}
@Override
protected Void doInBackground(ArrayList<Object>... params) {
String host = "api.twitter.com";
String twitterURL = "http://"+host+"/1/statuses/user_timeline.json?screen_name=i1990jain&count;=10";
try {
HttpClient client = new DefaultHttpClient();
BasicHttpContext localContext = new BasicHttpContext();
HttpHost targetHost = new HttpHost(host, 80, "http");
HttpGet httpget = new HttpGet(twitterURL);
httpget.setHeader("Content-Type", "application/json");
HttpResponse response = client.execute(targetHost, httpget, localContext);
HttpEntity entity = response.getEntity();
Object content = EntityUtils.toString(entity);
Log.d(MY_APP_TAG, "OK: " + content.toString());
JSONArray ja = new JSONArray(content.toString());
for(int i = 0; i < ja.length(); i++){
JSONObject jo = ja.getJSONObject(i);
listItems.add(jo.getString("text"));
}
} catch(Exception e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void result) {
dialog.dismiss();
}
}
}
public类主扩展ListActivity{
字符串MY_APP_TAG=“com.list”;
/**在首次创建活动时调用*/
@凌驾
创建时的公共void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
ArrayList listItems=新的ArrayList();
新建myAsyncTask().execute(listItems);
setListAdapter(新的ArrayAdapter(this,R.layout.tweet,R.id.tweet,listItems));
ListView lv=getListView();
lv.setTextFilterEnabled(真);
lv.setOnItemClickListener(新的OnItemClickListener(){
@凌驾
public void onItemClick(AdapterView父对象、视图、整型位置、长id){
//单击后,显示烤面包机
Toast.makeText(getApplicationContext(),((TextView)视图).getText(),Toast.LENGTH_SHORT.show();
}
});
}
私有类myAsyncTask扩展了AsyncTask
{
ArrayList列表项;
进程对话;
@凌驾
受保护的void onPreExecute(){
dialog=ProgressDialog.show(Main.this,“,”加载…);
}
@凌驾
受保护的Void doInBackground(ArrayList…params){
String host=“api.twitter.com”;
String twitterURL=“http://“+host+”/1/statuses/user\u timeline.json?screen\u name=i1990jain&;count;=10”;
试一试{
HttpClient=new DefaultHttpClient();
BasicHttpContext localContext=新的BasicHttpContext();
HttpHost targetHost=新的HttpHost(主机,80,“http”);
HttpGet HttpGet=新的HttpGet(twitterURL);
setHeader(“内容类型”、“应用程序/json”);
HttpResponse response=client.execute(targetHost、httpget、localContext);
HttpEntity=response.getEntity();
对象内容=EntityUtils.toString(实体);
Log.d(MY_APP_标记,“OK:+content.toString());
JSONArray ja=新的JSONArray(content.toString());
对于(int i=0;i
这是异步任务
。因此,您应该将其声明为AsyncTask
从
doInBackground
方法返回列表。要使用来自异步线程的新数据更新活动,可以使用onProgressUpdate()/onPostExecute()方法,或者如果您使用的是Thead,则应该使用Heandler
//aciticty class:
final Handler mHandler = new Handler();
//inside an async thread
handler.post(new Runnable() {
@Override
public void run() {
//update GUI thread here
}
});
您想在哪里返回结果?您可以在以下位置访问列表项:
protected void onPostExecute(Void result) {
这就是您应该使用listItems来填充列表的地方。此方法正在UI线程上运行,因此在其中运行是安全的
在您的doInBackground中,我没有看到listItems被初始化为任何值,因此它可能为null。实际上,您应该创建单独的listItems实例以在doInBackground中使用,然后将其分配给onPostExecute中的listView 我是怎么做到的
public class Main extends ListActivity {
String MY_APP_TAG = "com.vidyut";
ArrayList<Object> list = new ArrayList<Object>();
/** Called when the activity is first created. */
@SuppressWarnings("unchecked")
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
myAsyncTask task = new myAsyncTask();
task.execute();
}
private class myAsyncTask extends AsyncTask<ArrayList<Object>, ArrayList<Object>, ArrayList<Object>>
{
ProgressDialog dialog;
@Override
protected void onPreExecute() {
dialog = ProgressDialog.show(Main.this, "", "Loading....");
}
@Override
protected ArrayList<Object> doInBackground(ArrayList<Object>... params) {
String host = "api.twitter.com";
String twitterURL = "http://"+host+"/1/statuses/user_timeline.json?screen_name=i1990jain&count;=10";
try {
HttpClient client = new DefaultHttpClient();
BasicHttpContext localContext = new BasicHttpContext();
HttpHost targetHost = new HttpHost(host, 80, "http");
HttpGet httpget = new HttpGet(twitterURL);
httpget.setHeader("Content-Type", "application/json");
HttpResponse response = client.execute(targetHost, httpget, localContext);
HttpEntity entity = response.getEntity();
Object content = EntityUtils.toString(entity);
Log.d(MY_APP_TAG, "OK: " + content.toString());
JSONArray ja = new JSONArray(content.toString());
for(int i = 0; i < ja.length(); i++){
JSONObject jo = ja.getJSONObject(i);
list.add(jo.getString("text"));
}
} catch(Exception e) {
e.printStackTrace();
}
return list;
}
protected void onPostExecute(ArrayList<Object> list) {
dialog.dismiss();
Log.d(MY_APP_TAG, "The returned list contains " +list.size()+ "elements");
setListAdapter(new ArrayAdapter<Object>(Main.this, R.layout.tweet, R.id.tweet,list));
ListView lv = getListView();
lv.setTextFilterEnabled(true);
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
// When clicked, show a Toaster
Toast.makeText(getApplicationContext(), ((TextView) view).getText(), Toast.LENGTH_SHORT).show();
}
});
}
}
}
public类主扩展ListActivity{
字符串MY_APP_TAG=“com.vidyut”;
ArrayList=新建ArrayList();
/**在首次创建活动时调用*/
@抑制警告(“未选中”)
@凌驾
创建时的公共void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
myAsyncTask=新建myAsyncTask();
task.execute();
}
私有类myAsyncTask扩展了AsyncTask
{
进程对话;
@凌驾
受保护的void onPreExecute(){
dialog=ProgressDialog.show(Main.this,“,”加载…);
}
@凌驾
受保护的ArrayList doInBackground(ArrayList…参数){
String host=“api.twitter.com”;
String twitterURL=“http://“+host+”/1/statuses/user\u timeline.json?screen\u name=i1990jain&;count;=10”;
试一试{
HttpClient=new DefaultHttpClient();
BasicHttpContext localContext=新的BasicHttpContext();
HttpHost targetHost=新的HttpHost(主机,80,“http”);
HttpGet HttpGet=新的HttpGet(twitterURL);
setHeader(“内容类型”、“应用程序/json”);
HttpResponse response=client.execute(targetHost、httpget、localContext);
HttpEntity=response.getEntity();
对象内容=EntityUtils.toString(实体);
Log.d(MY_APP_标记,“OK:+content.toString());
JSONArray ja=新的JSONArray(content.toString());
对于(int i=0;i