Question

我是java的新手，我正在阅读有关listviews的内容如果我是对的，如果列表视图有数千个项目，它将消耗设备的内存，以避免我应该创建一个滚动侦听器，每次加载x项时都会加载更多的itens。正确？

我找到了这段代码，我正在尝试使用它，但在主要活动中，当我尝试实现它并设置onLoadMOre时，我不知道该怎么做。

public abstract class EndlessScrollListener implements AbsListView.OnScrollListener {
    // The minimum amount of items to have below your current scroll position
    // before loading more.
    private int visibleThreshold = 5;
    // The current offset index of data you have loaded
    private int currentPage = 0;
    // The total number of items in the dataset after the last load
    private int previousTotalItemCount = 0;
    // True if we are still waiting for the last set of data to load.
    private boolean loading = true;
    // Sets the starting page index
    private int startingPageIndex = 0;

    public EndlessScrollListener() {
    }

    public EndlessScrollListener(int visibleThreshold) {
        this.visibleThreshold = visibleThreshold;
    }

    public EndlessScrollListener(int visibleThreshold, int startPage) {
        this.visibleThreshold = visibleThreshold;
        this.startingPageIndex = startPage;
        this.currentPage = startPage;
    }

    // This happens many times a second during a scroll, so be wary of the code you place here.
    // We are given a few useful parameters to help us work out if we need to load some more data,
    // but first we check if we are waiting for the previous load to finish.
    @Override
    public void onScroll(AbsListView view,int firstVisibleItem,int visibleItemCount,int totalItemCount)
    {
        // If the total item count is zero and the previous isn't, assume the
        // list is invalidated and should be reset back to initial state
        if (totalItemCount < previousTotalItemCount) {
            this.currentPage = this.startingPageIndex;
            this.previousTotalItemCount = totalItemCount;
            if (totalItemCount == 0) { this.loading = true; }
        }
        // If it’s still loading, we check to see if the dataset count has
        // changed, if so we conclude it has finished loading and update the current page
        // number and total item count.
        if (loading && (totalItemCount > previousTotalItemCount)) {
            loading = false;
            previousTotalItemCount = totalItemCount;
            currentPage++;
        }

        // If it isn’t currently loading, we check to see if we have breached
        // the visibleThreshold and need to reload more data.
        // If we do need to reload some more data, we execute onLoadMore to fetch the data.
        if (!loading && (totalItemCount - visibleItemCount)<=(firstVisibleItem + visibleThreshold)) {
            onLoadMore(currentPage + 1, totalItemCount);
            loading = true;
        }
    }

    // Defines the process for actually loading more data based on page
    public abstract void onLoadMore(int page, int totalItemsCount);

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // Don't take any action on changed
    }
}

mycode的：

public class MainActivity extends ActionBarActivity implements EndlessScrollListener{

    List<Paises> paisesList = new ArrayList<Paises>();
    EditText j_search;

    ListView j_listview;

    String[] j_paises;
    String[] j_nota;

  PaisesAdapter j_adapter;


    int[] j_flags  =
            {
                    R.drawable.flag_brazil,
                    R.drawable.flag_bolivia,
                    R.drawable.flag_argentina,
                    R.drawable.flag_chile,
                    R.drawable.flag_colombia,
                    R.drawable.flag_equador,
                    R.drawable.flag_france,
                    R.drawable.flag_guyana,
                    R.drawable.flag_paraguay,
                    R.drawable.flag_peru,
                    R.drawable.flag_suriname,
                    R.drawable.flag_uruguay,
                    R.drawable.flag_venezuela

            };


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);



        j_paises = getResources().getStringArray(R.array.r_arrayPais);
        j_nota = getResources().getStringArray(R.array.r_arrayNota);

        j_listview = (ListView)findViewById(R.id.l_lView);
        j_search = (EditText)findViewById(R.id.l_searchView);

        j_adapter = new PaisesAdapter(this, paisesList);


        j_adapter.notifyDataSetChanged();
        j_listview.setAdapter(j_adapter);
        j_listview.setChoiceMode(AbsListView.CHOICE_MODE_SINGLE);


        int i = 0;
        for(String paises : j_paises)
        {
            Paises dataProvider = new Paises(j_flags[i], paises, j_nota[i]);
            j_adapter.add(dataProvider);
            i++;
        }

        Collections.sort(paisesList, new AbcComparator());

        j_listview.setTextFilterEnabled(true);
        j_search.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                System.out.println("Text ["+s+"]");
                j_adapter.getFilter().filter(s.toString());
            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }


    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onLoadMore(int page, int totalItemsCount) {

    }


}

Answer 1

在这种情况下，您需要处理存储在适配器中的项目。适配器是处理模型列表（项目，数据）的适配器。

假设，如果你的适配器

扩展ArrayAdapter
有一个getter / setter来更新其项目列表MyAdapter.getItems()/setItems(List<Item> newItems)

您可以使用适配器或列表视图，然后

@Override
public void onLoadMore(int page, int totalItemsCount) {
    // download or fetch next page(s) items, then add them to your adapter list
    List<Item> newPageOfItems = .....;

    // if list view reference, cast and get a reference to your adapter
    MyAadapter myAdapter = (MyAdapter) listView.getAdapter();

    if (newPageOfItems != null && !newPageOfItems.isEmpty()) {
        List<Item> currentItems = myAdapter.getItems();
        currentItems.addAll(newPageOfItems);
        currentItems.setItems(currentItems);
        // if for some reason new page is not updated properly, uncomment below
        // myAdapter.notifyDataSetChanged();
    }
}

无尽的滚动侦听器

1 个答案: