问题描述

OnScrollListener中的方法没有执行

  给一个girdview设置一个自定义的ArrayAdapter,该适配器同时实现了OnScrollListener接口，但是OnScrollListener中的onScroll() 以及在滑动gridview的时候onScrollStateChanged()都没有执行，自定义的ArrayAdapter中的geiView（）执行正常，这段代码主要是现实从SD卡读取图片并显示在gridview中，代码如下：
        public class PhotoGalleryFragment extends Fragment {

private static final String TAG = "PhotoGalleryFragment";

private GridView mGridView;
private ArrayList<GalleryItem> mItems;
private PhotoLoader<ImageView> mPhotoLoader;
private int mFirstVisibleItem,mVisibleItemCount;
//用于判断是否是第一次打开应用，解决第一次进入应用，图片不加载的问题
private boolean mIsFirstIn = true;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setRetainInstance(true);

    new FetchItemsTask().execute();
    //new FetchItemsTask().cancel();
    mPhotoLoader = new PhotoLoader<>(new Handler(),getActivity());
    mPhotoLoader.setmListener(new PhotoLoader.Listener<ImageView>() {
        @Override
        public void onPhotoLoadered(ImageView imageView, Bitmap bitmap) {
            if (isVisible()) imageView.setImageBitmap(bitmap);
        }
    });
    mPhotoLoader.start();
    mPhotoLoader.getLooper();
    Log.d(TAG, "backgrounp thread started");
}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.fragment_photo_gallery,container,false);

    mGridView = (GridView) view.findViewById(R.id.gridView);

    setupAdapter();
    return view;
}

private class FetchItemsTask extends AsyncTask<Void,Void,ArrayList<GalleryItem>>{

    @Override
    protected ArrayList<GalleryItem> doInBackground(Void... params) {
        Log.d(TAG,"doInBackground");
        return new PhotosFetchr().fetchItems();
    }

    @Override
    protected void onPostExecute(ArrayList<GalleryItem> galleryItems) {
        mItems = galleryItems;
        setupAdapter();
        //GalleryItemAdapter adapter = (GalleryItemAdapter)mGridView.getAdapter();
        //adapter.notifyDataSetChanged();
    }
}

private void setupAdapter(){
    //Log.d(TAG,"mItems size = " +mItems.size());
    if(getActivity() == null || mGridView == null) return;
    if(mItems != null){
        mGridView.setAdapter(new GalleryItemAdapter(mItems));
    }else {
        mGridView.setAdapter(null);
    }
}

private class GalleryItemAdapter extends ArrayAdapter<GalleryItem> implements AbsListView.OnScrollListener{

    public GalleryItemAdapter(ArrayList<GalleryItem> mItems) {
        super(getActivity(), 0, mItems);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Log.d(TAG,"getView" );
        if(convertView == null){
            convertView = getActivity().getLayoutInflater().inflate(R.layout.gallery_item,parent,false);
        }
        ImageView imageView = (ImageView) convertView.findViewById(R.id.gallery_item_imageView);
        imageView.setImageResource(R.mipmap.icon1);
        GalleryItem item = getItem(position);
        imageView.setTag(item.getPhotoName());
        //mPhotoLoader.queueLoader(imageView,item.getPhotoName());
        return convertView;
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        Log.d(TAG,"onScrollStateChanged scrollState = " + scrollState );
        if(scrollState == SCROLL_STATE_IDLE){
            loadImage(mFirstVisibleItem,mVisibleItemCount);
        }else{
            mPhotoLoader.clearQueue();
        }

    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        Log.d(TAG,"onScroll" +" firstVisibleItem = "+firstVisibleItem+" visibleItemCount = "+visibleItemCount);
        mFirstVisibleItem = firstVisibleItem;
        mVisibleItemCount = visibleItemCount;
        //首次进入时加载图片
        if(mIsFirstIn && visibleItemCount > 0){
            loadImage(mFirstVisibleItem,mVisibleItemCount);
            mIsFirstIn = false;

        }
    }
}

@Override
public void onDestroyView() {
    super.onDestroyView();
    mPhotoLoader.clearQueue();
}

@Override
public void onDestroy(){
    super.onDestroy();
    mPhotoLoader.quit();
    Log.d(TAG, "backgrounp thread destroyed");
}

public void loadImage(int firstVisibleItem,int visibleItemCount){
    Log.d(TAG,"loadImage");
    for(int i =firstVisibleItem;i<firstVisibleItem + visibleItemCount;i++){
        String photoName = mItems.get(i).getPhotoName();
        ImageView imageView = (ImageView) mGridView.findViewWithTag(photoName);
        mPhotoLoader.queueLoader(imageView,photoName);
    }
}

}

解决方案

你应该给listview设置监听器，你只说给它设置了适配器。mGridView.setOnScrollListener（new GalleryItemAdapter(mItems)）；
为什么用适配器实现监听接口？

解决方案二：

Silverlight 中 OnApplyTemplate方法没有执行