如何在不冻结程序的情况下更新ListView

Question

So I have a list of strings (ISBNs), and I need to fill a listview with the objects (Book objects) associated with these strings . The problem is that the function I have to get the Book object using the string takes time, and so to get, say 30 books, the wait approaches 4 or 5 seconds.

One approach I've thought of is to get the Book objects one at a time, and to add them to the list as I get them. But this process will freeze the UI until it's done adding them all. If I try to put this process in a new thread, it won't let me add to the any UI objects (since it's from another thread). If I try to put it in an AsyncTask , I can't access the ListView since it's in the MainActivity class.

There must be a way to dynamically update a UI element, I'm sure I've seen it done. Any suggestions?

EDIT :

This is the code I'm using to actually add items to the list:

//List view and adapter setup
listView = (ListView) findViewById(R.id.listViewCheckout);
bookAdapter = new SearchBookAdapter(getApplicationContext(), R.layout.search_row_layout);
listView.setAdapter(bookAdapter);

for(int i = 0; i < searches.size(); i++) {

    //Get the book
    Book book = BackendFunctions.getBookFromISBN(fbSnapshot, searches.get(i));

    //Assign data to the adapter variables
    Bitmap cover = book.getCover();
    String title = book.getTitle();
    String author = book.getAuthor();

    //Add data to the adapter and set the list
    SearchBookDataProvider dataProvider = new SearchBookDataProvider(cover, title, author);
    bookAdapter.add(dataProvider);
    bookAdapter.notifyDataSetChanged();
}

Answer 1

Can you make some changes to your code like this it simple it think it will work

//List view and adapter setup
listView = (ListView) findViewById(R.id.listViewCheckout);
bookAdapter = new SearchBookAdapter(getApplicationContext(), R.layout.search_row_layout);
SearchBookDataProvider dataProvider;
listView.setAdapter(bookAdapter);

 new AsyncTask() {
            @Override
            protected Object doInBackground(Object[] objects) {
                for(int i = 0; i < searches.size(); i++) {

                //Get the book
                Book book = BackendFunctions.getBookFromISBN(fbSnapshot, searches.get(i));

                //Assign data to the adapter variables
                Bitmap cover = book.getCover();
                String title = book.getTitle();
                String author = book.getAuthor();

                //Add data to the adapter and set the list
                dataProvider = new SearchBookDataProvider(cover, title, author);
                bookAdapter.add(dataProvider);
                }
            }
            @Override
            protected void onPostExecute(Object o) {
                if (bookAdapter!= null) {
                    bookAdapter.notifyDataSetChanged();
                }
                super.onPostExecute(o);
            }
 }.execute();

Answer 2

you can use TimerTask to update the listview or runUiThread() or doInBackground(). But remember should use notifysetChanges() when you update the list.

Answer 3

Step 1: Declare a Executer service

 private ExecutorService mExecuterService = null;

Step 2:Declare a class for your list iteration and view update

  class ListViewUpdater implements Runnable{

            public ListViewUpdater(/* if you need you can pass list params here */){

            }

            @Override
            public void run() {
                for(int i = 0; i < searches.size(); i++) {

                    //Get the book
                    Book book = BackendFunctions.getBookFromISBN(fbSnapshot, searches.get(i));

                    //Assign data to the adapter variables
                    Bitmap cover = book.getCover();
                    String title = book.getTitle();
                    String author = book.getAuthor();



                }
//below code is important for Updating UI ,you should run UI Updates in UI thread
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        bookAdapter.notifyDataSetChanged();
                    }
                });
            }
        }

Step 3: Initilize and call below methods

//Add data to the adapter and set the list
    SearchBookDataProvider dataProvider = new SearchBookDataProvider(cover, title, author);
   bookAdapter.add(dataProvider);
    mExecuterService = Executors.newSingleThreadExecutor()
    mExecuterService.execute(new ListViewUpdater());

It may solve your problems.

Answer 4

I think if you are open to use a open source project ,then my suggestion will be use RX-JAVA.Which is based in reactive and push based model.

link for rx-java .

rx-java example .

Answer 5

You can get the list of the books in a Thread and send a Broadcast with the data received. Register a broadcast receiver in your MainActivity class and update the Adapter in the receiver. That should not freeze the UI.

EDIT -

  BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        Book book = (Book)intent.getSerializableExtra("Book");
        SearchBookDataProvider dataProvider = new SearchBookDataProvider(cover, title, author);
        bookAdapter.add(dataProvider);
        bookAdapter.notifyDataSetChanged();
    }
};

Thread thread = new Thread(){
    @Override
    public void run()
    {
        for(int i = 0; i < searches.size(); i++) {

            //Get the book
            Book book = BackendFunctions.getBookFromISBN(fbSnapshot, searches.get(i));

            Intent intent = new Intent();
            intent.setAction("Book Received");
            intent.putExtra("Book",book);
            sendBroadcast(intent);
        }
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    listView = (ListView) findViewById(R.id.listView);
    listView.setAdapter(bookAdapter);
    registerReceiver(broadcastReceiver,new IntentFilter("Book Received"));
    thread.start();

}