我在这里有一个问题，正确设置listview适配器。我有一个listview，它从AsyncTask获取数据，然后从Json格式的Web服务获取其信息，并且Data仅在AsyncTask的OnPostExecute方法中可用，并且我在那里设置了我的适配器。问题是频繁出现新信息，每次设置适配器都会导致性能下降。当信息进入AsyncTask时，如何设置适配器一次？这是我的活动......
public class Myprofile extends Activity {
String URI_URL;
Integer page;
ProgressBar pb;
ListView mm;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.myprofile);
URI_URL = getResources().getString(R.string.PathUrl) + "/api/myprofile";
page=0;
new Myprofile_Async().execute();
// Listview for adapter
mm= (ListView)findViewById(R.id.myprofiles);
// Listview to use inside scroll event
final ListView lv=(ListView)findViewById(R.id.myprofiles);
lv.setOnScrollListener(new AbsListView.OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// fires off when scroll close to bottom
if (scrollState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE && (lv.getLastVisiblePosition() - lv.getHeaderViewsCount() - lv.getFooterViewsCount()) >= (view.getCount() - 1)) {
new Myprofile_Async().execute();
}
}
@Override
public void onScroll(AbsListView absListView, int i, int i1, int i2) {
}
});
}
public class Myprofile_Async extends AsyncTask<String,String,String> {
HttpURLConnection conn;
URL url;
String result="";
DataOutputStream wr;
int id;
@Override
protected void onPreExecute() {
super.onPreExecute();
pb=(ProgressBar)findViewById(R.id.progressBar);
pb.setVisibility(View.VISIBLE);
id= getIntent().getExtras().getInt("id");
// page Int is used to keep count of scroll events
if(page==0)
{page=1;}
else {page=page+1;}
Toast.makeText(Myprofile.this,""+page,Toast.LENGTH_SHORT).show();
}
@Override
protected String doInBackground(String... params) {
// Gets data from api
BufferedReader reader=null;
String cert="id="+id+"&page="+page;
try{
url = new URL(URI_URL);
conn = (HttpURLConnection) url.openConnection();
conn.setDoOutput(true);
conn.setRequestMethod("POST");
conn.connect();
conn.setReadTimeout(10000);
conn.setConnectTimeout(15000);
wr = new DataOutputStream(conn.getOutputStream());
wr.writeBytes(cert);
wr.flush();
wr.close();
reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
StringBuilder sBuilder = new StringBuilder();
String line = "";
while ((line = reader.readLine()) != null) {
sBuilder.append(line + "\n");
}
result = sBuilder.toString();
reader.close();
conn.disconnect();
return result;
}
catch (Exception e)
{
e.printStackTrace();
}
System.err.println("cassies"+ result);
return result;
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
try {
// Data is returned in Json Format
JSONObject jsonn= new JSONObject(result);
JSONArray jArray = jsonn.getJSONArray("myprofile");
JSONObject jobject=null;
JSONArray sss= new JSONArray();
for(int i=0; i < jArray.length(); i++) {
jobject= jArray.getJSONObject(i);
jobject.getString("post");
jobject.getString("fullname");
sss.put(jobject);
}
jsonn.put("myprofile", sss);
// Callout BaseAdapter to populate columns
Myprofile_CustomView BA=new Myprofile_CustomView(jsonn,Myprofile.this);
// Set the adapter notice the data comes from BaseAdapter BA
mm.setAdapter(DMF);
} catch (Exception e) {
}
pb.setVisibility(View.INVISIBLE);
}
}
}
}
这是我更新的代码
public class Myprofile extends Activity {
String URI_URL;
Integer page;
ProgressBar pb;
ListView mm;
Myprofile_CustomView BA;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.myprofile);
URI_URL = getResources().getString(R.string.PathUrl) + "/api/myprofile";
page=0;
new Myprofile_Async().execute();
// Listview for adapter
mm= (ListView)findViewById(R.id.myprofiles);
mm.setAdapter(BA);
// Listview to use inside scroll event
/*
final ListView lv=(ListView)findViewById(R.id.myprofiles);
lv.setOnScrollListener(new AbsListView.OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// fires off when scroll close to bottom
if (scrollState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE && (lv.getLastVisiblePosition() - lv.getHeaderViewsCount() - lv.getFooterViewsCount()) >= (view.getCount() - 1)) {
new Myprofile_Async().execute();
}
}
@Override
public void onScroll(AbsListView absListView, int i, int i1, int i2) {
}
});
*/
}
public class Myprofile_Async extends AsyncTask<String,String,String> {
HttpURLConnection conn;
URL url;
String result="";
DataOutputStream wr;
int id;
@Override
protected void onPreExecute() {
super.onPreExecute();
pb=(ProgressBar)findViewById(R.id.progressBar);
pb.setVisibility(View.VISIBLE);
id= getIntent().getExtras().getInt("id");
// page Int is used to keep count of scroll events
if(page==0)
{page=1;}
else {page=page+1;}
Toast.makeText(Myprofile.this,""+page,Toast.LENGTH_SHORT).show();
}
@Override
protected String doInBackground(String... params) {
// Gets data from api
BufferedReader reader=null;
String cert="id="+id+"&page="+page;
try{
url = new URL(URI_URL);
conn = (HttpURLConnection) url.openConnection();
conn.setDoOutput(true);
conn.setRequestMethod("POST");
conn.connect();
conn.setReadTimeout(10000);
conn.setConnectTimeout(15000);
wr = new DataOutputStream(conn.getOutputStream());
wr.writeBytes(cert);
wr.flush();
wr.close();
reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
StringBuilder sBuilder = new StringBuilder();
String line = "";
while ((line = reader.readLine()) != null) {
sBuilder.append(line + "\n");
}
result = sBuilder.toString();
reader.close();
conn.disconnect();
return result;
}
catch (Exception e)
{
e.printStackTrace();
}
System.err.println("cassies"+ result);
return result;
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
try {
// Data is returned in Json Format
JSONObject jsonn= new JSONObject(result);
JSONArray jArray = jsonn.getJSONArray("myprofile");
JSONObject jobject=null;
JSONArray sss= new JSONArray();
for(int i=0; i < jArray.length(); i++) {
jobject= jArray.getJSONObject(i);
jobject.getString("post");
jobject.getString("fullname");
sss.put(jobject);
}
System.err.println("mpee: "+ sss);
jsonn.put("myprofile", sss);
// Callout BaseAdapter
// Myprofile_CustomView DMF=new Myprofile_CustomView(jsonn,Myprofile.this);
// Set the adapter again
BA.updateResults(jsonn,Myprofile.this);
BA.notifyDataSetChanged();
} catch (Exception e) {
System.err.println("mpee: " + e.toString());
}
pb.setVisibility(View.INVISIBLE);
}
}
}
这是我的BaseAdapter
public class Myprofile_CustomView extends BaseAdapter {
JSONObject names;
Context ctx;
LayoutInflater myiflater;
// Have data come in and do a toast to see changes
public Myprofile_CustomView(JSONObject arr, Context c) {
notifyDataSetChanged();
ctx = c;
names = arr;
myiflater = (LayoutInflater) c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
public void updateResults(JSONObject results, Context c) {
names=results;
ctx=c;
notifyDataSetChanged();
Toast.makeText(c,names+"",Toast.LENGTH_SHORT).show();
}
@Override
public int getCount() {
try {
JSONArray jaLocalstreams = names.getJSONArray("myprofile");
return jaLocalstreams.length();
} catch (Exception e) {
Toast.makeText(ctx, "Error: Please try again", Toast.LENGTH_LONG).show();
return names.length();
}
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View row=convertView;
MyViewHolder holder=null;
try {
if(row==null) {
LayoutInflater li = (LayoutInflater) ctx.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
row = li.inflate(R.layout.zmyprofile,parent,false);
holder=new MyViewHolder(row);
row.setTag(holder);
// Log.d("VIX", "Creating new Row");
}
else
{
holder=(MyViewHolder)row.getTag();
// Log.d("VIX", "Recycling");
}
JSONArray jaLocalstreams = names.getJSONArray("myprofile");
final JSONObject jsonObject = jaLocalstreams.getJSONObject(position);
holder.post.setText(jsonObject.getString("post"));
holder.fullname.setText(jsonObject.getString("fullname"));
return row;
} catch (Exception e) {
e.printStackTrace();
}
return row;
}
class MyViewHolder{
TextView post,fullname;
MyViewHolder(View v)
{
post= (TextView)v.findViewById(R.id.post);
fullname= (TextView)v.findViewById(R.id.fullname);
}
}
}
答案 0 :(得分：0)
适配器通常采用物品清单。
您可以在onCreate中定义一个空的项目列表，然后传递给您的适配器。
现在，当你获得新数据时，只需更新该项目列表，然后调用此函数告诉Adapter数据已更改。
yourAdapterObject.notifyDataSetChanged();
答案 1 :(得分：0)
您可以使用notifyDataSetChanged方法。在适配器类中：
private List myList;
...
...
public void update(List newList) {
myList = newList;
notifyDataSetChanged();
}
您第一次定义适配器，在下次更新中，您只使用新列表调用更新方法。
答案 2 :(得分：0)
Sharj是正确的，因为您可以向现有（空）适配器添加新数据。没有必要调用该方法 .notifyDataSetChanged（） 因为这是在适配器代码内部调用的。
请参阅显示内部呼叫的source for ArrayAdapter。