Question

我有一个带有标签式布局的Android应用程序，其中包含列表视图。我在从服务器检索信息后尝试更新列表。但是，在触摸屏幕之前，列表不会更新。所有信息都是正确的，但无论我等多久，列表都不会填充屏幕，直到我点击它为止。有谁知道如何解决这个问题？

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对这个问题是正确的，但还有一些我不得不改变的事情。

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();
    }

Answer 1

在Tab1.java中，您有方法retrievePosts()，其中包含AsyncTask。在此AsyncTask的doInBackground()内，您拨打newAdapter.updateList()，在updateList()内拨打notifyDataSetChanged()。

文档here说，notifyDataSetChanged()刷新了用户界面。但据我所知，刷新UI应该只能从UI线程，而不是从任何后台线程。您可以尝试在AsyncTask中的newAdapter.updateList()中调用onPostExecute()，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：我认为如果没有像e.printStackTrace()等那样的事情就抓住所有例外情况是不好的。

Android标签视图直到触摸才更新

1 个答案: