我有一个带有选项卡式布局的 Android 应用程序,其中包含 ListView 。我正在尝试从服务器检索信息后更新列表。但是,在触摸屏幕之前该列表不会更新。所有信息都是正确的,但无论我等待多久,该列表都不会填充屏幕,直到我点击它。有谁知道如何解决这个问题吗?
Tab1.java
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
/**
* Created by hp1 on 21-01-2015.
*/
//NEW
public class Tab1 extends Fragment {
MainActivity mainActivity;
List<Post> postList;
public static NewAdapter newAdapter;
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View v =inflater.inflate(R.layout.tab_1,container,false);
return v;
}
@Override
public void onStart() {
super.onStart();
postList = new ArrayList<Post>();
try {
//get data from azure
mainActivity = (MainActivity) getActivity();
//set lists
ListView newListView = (ListView) mainActivity.findViewById(R.id.newListView);
newAdapter = new NewAdapter(mainActivity, postList);
newListView.setAdapter(newAdapter);
}catch(Exception e){
}
//get the posts loaded asynchronously
retrievePosts();
}
public void retrievePosts(){
AsyncTask<Void,Void,Void> task = new AsyncTask<Void,Void,Void>(){
@Override
protected Void doInBackground(Void... params) {
try {
postList= mainActivity.postTable.execute().get();
Log.e("TAG",postList.get(0).text);
newAdapter.updateList(postList);
} catch (final Exception e) {
}
return null;
}
};
runAsyncTask(task);
}
private AsyncTask<Void, Void, Void> runAsyncTask(AsyncTask<Void, Void, Void> task) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
return task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
} else {
return task.execute();
}
}
}
NewAdapter.java
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;
import android.widget.Toast;
import java.util.List;
public class NewAdapter extends BaseAdapter {
List<Post> postList;
Context context;
LayoutInflater inflater;
public NewAdapter(MainActivity mainActivity, List<Post> myPostList) {
postList=myPostList;
context=mainActivity;
inflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return postList.size();
}
@Override
public Object getItem(int position) {
return postList.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
PostCell postCell=new PostCell();
View cellView = inflater.inflate(R.layout.post_cell, null);
postCell.textView=(TextView) cellView.findViewById(R.id.textView1);
postCell.textView.setText(postList.get(position).text);
cellView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(context, "You Clicked "+postList.get(position).text, Toast.LENGTH_LONG).show();
}
});
return cellView;
}
public List<Post> updateList(List<Post> myPostList){
postList = myPostList;
notifyDataSetChanged();
return postList;
}
public List<Post> addToList(Post post){
postList.add(post);
notifyDataSetChanged();
return postList;
}
}
编辑:最终答案 - 这是我解决问题的最终代码。 Bnydev 对这个问题的看法是正确的,但还有一些事情我还必须更改。
public void retrievePosts(){
//NOTE: must have a return type for an async task to run onpostexecute, which
//is executed on the ui thread so the screen can be updated
AsyncTask<Void,Void,Boolean> task = new AsyncTask<Void,Void,Boolean>(){
@Override
protected Boolean doInBackground(Void... params) {
try {
postList= mainActivity.postTable.execute().get();
} catch (final Exception e) {
e.printStackTrace();
}
return true;
}
protected void onPostExecute(Boolean reult) {
newAdapter.updateList(postList);
}
};
task.execute();
}
最佳答案
在 Tab1.java 中,您有方法 retrievePosts()
,它包含一个 AsyncTask。在此 AsyncTask 的 doInBackground()
中,您调用 newAdapter.updateList()
,并在 updateList()
中调用 notifyDataSetChanged( )
。
文档 here表示 notifyDataSetChanged()
刷新 UI。但据我所知,刷新 UI 只能从 UI 线程进行,而不是从任何后台线程进行。您可以尝试在 AsyncTask 内的 onPostExecute()
中调用 newAdapter.updateList()
,请参阅示例 here 。 doInBackground()
在后台线程上执行,onPostExecute()
在 UI 线程上执行。
public void retrievePosts(){
AsyncTask<Void,Void,Void> task = new AsyncTask<Void,Void,Void>(){
@Override
protected Void doInBackground(Void... params) {
try {
postList= mainActivity.postTable.execute().get();
Log.e("TAG",postList.get(0).text);
} catch (final Exception e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute() {
newAdapter.updateList(postList);
}
};
runAsyncTask(task);
}
PS:我认为在没有诸如 e.printStackTrace()
等的情况下捕获所有异常并不好。
关于java - Android 选项卡式 View 在触摸之前不会更新,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/39176631/