在Android应用程序中为网格视图图像实现无限滚动

Question

我正在构建一个谷歌图片搜索器应用程序，它以网格视图返回结果。我想实现无限滚动机制来异步加载图像。我为EndlessScrolling创建了一个新类。我无法确定用于onLoadMore方法和customLoadMoreDataFromApi的逻辑。我发布了我的主要活动和我创建的EndlessScrolling类。

SearchActivity.java

package com.example.gridimagesearch;

import java.util.ArrayList;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.content.DialogInterface.OnClickListener;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.GridView;
import android.widget.Toast;

import com.loopj.android.http.AsyncHttpClient;
import com.loopj.android.http.JsonHttpResponseHandler;

public class SearchActivity extends Activity {
    EditText etQuery;
    GridView gvResults;
    Button btnSearch;
    ArrayList<ImageResults> imageResults= new ArrayList<ImageResults>();
    ImageResultsArrayAdapter imageAdapter;
    private final int REQUEST_CODE=20;
    String imageSize;
    String colorFilter;
    String imageType;
    String siteFilter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_search);
        setViews();
        imageAdapter= new ImageResultsArrayAdapter (this, imageResults);
        gvResults.setAdapter(imageAdapter);
        gvResults.setOnScrollListener(new EndlessScrollListener() {
            @Override
            public void onLoadMore(int page, int totalItemsCount) {
                    // Triggered only when new data needs to be appended to the list
                    // Add whatever code is needed to append new items to your AdapterView
                customLoadMoreDataFromApi(page); 
                    // or customLoadMoreDataFromApi(totalItemsCount); 
                }
            });

        gvResults.setOnItemClickListener(new OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> adapter, View parent, int position,long rowId) {
                    Intent i = new Intent(SearchActivity.this, ImageDisplayActivity.class);
                    ImageResults imageResult = imageResults.get(position);
                    i.putExtra("results", imageResult);
                    startActivity(i);
                }
        });

    }


    public void onAdvSearch(MenuItem mi){
        Intent i = new Intent(SearchActivity.this, AdvancedSearchActivity.class);
        i.putExtra("mode",2);
        startActivityForResult(i, REQUEST_CODE);
    }

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
          if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {

              imageSize = data.getExtras().getString("imagesize");
              colorFilter = data.getExtras().getString("colorfilter");
              imageType = data.getExtras().getString("imagetype");
              siteFilter = data.getExtras().getString("sitefilter");
              //Toast.makeText(this, imageSize, Toast.LENGTH_SHORT).show();
            }
          }


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

    public void setViews(){
        etQuery=(EditText) findViewById(R.id.etQuery);
        gvResults=(GridView)findViewById(R.id.gvResults);
        btnSearch=(Button)findViewById(R.id.btnSearch);
    }

    public void onImageSearch(View v){
        String query=etQuery.getText().toString();
        Toast.makeText(this, "Searching for " +query, Toast.LENGTH_SHORT).show();
        AsyncHttpClient client = new AsyncHttpClient();
        client.get("https://ajax.googleapis.com/ajax/services/search/images?rsz=8&" + "start=" + 0 + "&v=1.0&q=" + Uri.encode(query) + "&imgsz=" + Uri.encode(imageSize) + "&imgcolor=" + Uri.encode(colorFilter) + "&imgtype=" + Uri.encode(imageType) + "&as_sitesearch=" + Uri.encode(siteFilter), new JsonHttpResponseHandler(){

            @Override
            public void onSuccess(JSONObject response) {
                JSONArray imageJsonResults=null;
                try{
                    imageJsonResults=response.getJSONObject("responseData").getJSONArray("results");
                    imageResults.clear();
                    imageAdapter.addAll(ImageResults.fromJSONArray(imageJsonResults));
                    Log.d("DEBUG", imageResults.toString());
                }catch (JSONException e){
                    e.printStackTrace();
                }

            }
        });
    }

}

EndlessScrolling Class

package com.example.gridimagesearch;

import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;

public abstract class EndlessScrollListener implements 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 data set 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;
        }


        @Override
        public void onScroll(AbsListView view,int firstVisibleItem,int visibleItemCount,int totalItemCount) 
            {

            if (!loading && (totalItemCount < previousTotalItemCount)) {
                this.currentPage = this.startingPageIndex;
                this.previousTotalItemCount = totalItemCount;
                if (totalItemCount == 0) { this.loading = true; } 
            }


            if (loading) {
                if (totalItemCount > previousTotalItemCount) {
                    loading = false;
                    previousTotalItemCount = totalItemCount;
                    currentPage++;
                }
            }


            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
        }
}

有人可以告诉我如何实现onLoadMore方法以使其正常工作。

感谢。