请帮我解决有关网格视图的问题。目前我正在开发一个图库应用程序，其中显示图像的网格视图。现在，问题是每次我通过触发滚动方法在网格视图上加载更多项目时，UI在显示新加载的项目之前滞后一段时间。我只想修复滞后，或者你可以提出一些改进我的网格视图的想法或技巧。也许，如果可能的话，你可以给我一个关于如何在网格视图底部放置一个进度条的想法，该进度条将在添加网格视图项目时显示，并在添加网格视图项目后消失
这些是代码：
这是实现on scroll方法的主要活动，当触发scroll方法时，如果满足条件，它将调用Utils的GenerateData内部类，该类扩展AsyncTask并返回数组列表和此数组列表将被添加到主要活动的数组中。
GridViewActivity：
public class GridViewActivity extends Activity implements AbsListView.OnScrollListener, AbsListView.OnItemClickListener{
private GridView gridView;
private GridViewImageAdapter adapter;
private Utils utils;
private GenerateData generateData;
private ArrayList<HashMap<String, String>> galleryAttributes;
private int columnWidth;
private int urlPageIndex = 1;
private boolean hasRequestedMore;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_grid_view);
setTitle("Gallery");
gridView = (GridView) findViewById(R.id.grid_view);
utils = new Utils(this);
InitializeGridLayout();
galleryAttributes = new ArrayList<HashMap<String, String>>();
generateData = utils.new GenerateData(urlPageIndex);
try {
galleryAttributes.addAll(generateData.execute().get());
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
adapter = new GridViewImageAdapter(GridViewActivity.this, galleryAttributes , columnWidth);
gridView.setAdapter(adapter);
gridView.setOnScrollListener(this);
gridView.setOnItemClickListener(this);
}
public void InitializeGridLayout() {
Resources r = getResources();
float padding = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,AppConstant.GRID_PADDING, r.getDisplayMetrics());
columnWidth = (int) ((utils.getScreenWidth() - ((AppConstant.NUM_OF_COLUMNS + 1) * padding)) / AppConstant.NUM_OF_COLUMNS);
gridView.setNumColumns(AppConstant.NUM_OF_COLUMNS);
gridView.setColumnWidth(columnWidth);
gridView.setStretchMode(GridView.NO_STRETCH);
gridView.setPadding((int) padding, (int) padding, (int) padding,(int) padding);
gridView.setHorizontalSpacing((int) padding);
gridView.setVerticalSpacing((int) padding);
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
// TODO Auto-generated method stub
Intent intent = new Intent(GridViewActivity.this,
CarouselViewActivity.class);
intent.putExtra("position", position);
intent.putExtra("galleryAttributes", galleryAttributes);
startActivity(intent);
Log.e("onItemClick: ", "" + position);
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
Log.e("onScrollStateChanged: ", "" + scrollState);
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
// TODO Auto-generated method stub
Log.e("onScroll: ", "firstVisibleItem:" + firstVisibleItem
+ " visibleItemCount:" + visibleItemCount + " totalItemCount:"
+ totalItemCount);
if (!hasRequestedMore) {
int lastInScreen = firstVisibleItem + visibleItemCount;
if (lastInScreen >= totalItemCount) {
hasRequestedMore = true;
onLoadMoreItems();
}
}
}
public void onLoadMoreItems() {
if (urlPageIndex < 3) {
urlPageIndex++;
generateData = utils.new GenerateData(urlPageIndex);
try {
galleryAttributes.addAll(generateData.execute().get());
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
adapter.notifyDataSetChanged();
hasRequestedMore = false;
}
}
}
这是我的Utils类，这个类负责从Json检索数据并将其放在将从其调用者返回的数组列表中。
的Utils：
public class Utils {
private Context context;
private ProgressDialog progressDialog;
public Utils(){}
public Utils(Context context){
this.context = context;
}
public class GenerateData extends AsyncTask<Void, Void, ArrayList<HashMap<String, String>>>{
private JSONArray dataJsonArr;
private JsonParser jParser;
private JSONObject json;
private JSONObject c;
private HashMap<String, String> map;
private ArrayList<HashMap<String,String>> galleryAttributes;
private int urlPageIndex;
private GridViewImageAdapter gridViewAdapter;
private boolean onLoadMore = false;
public GenerateData(int urlPageIndex){
this.urlPageIndex = urlPageIndex;
new InitializeJsonArray().execute();
}
@Override
protected ArrayList<HashMap<String, String>> doInBackground(
Void... params) {
// TODO Auto-generated method stub
try{
for(int i = 0; i< dataJsonArr.length(); i++)
{
c = dataJsonArr.getJSONObject(i);
map = new HashMap<String, String>();
map.put("Link", c.getString("Link"));
galleryAttributes.add(map);
}
}
catch (JSONException e) {
e.printStackTrace();
}
return galleryAttributes;
}
public class InitializeJsonArray extends AsyncTask<Void, Void, Void>{
@Override
protected Void doInBackground(Void... params) {
// TODO Auto-generated method stub
dataJsonArr = null;
jParser = new JsonParser();
json = jParser.getJSONFromUrl(AppConstant.JSON_URL+urlPageIndex);
try {
dataJsonArr = json.getJSONArray(AppConstant.JSON_ARRAY_NAME);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
galleryAttributes = new ArrayList<HashMap<String, String>>();
galleryAttributes.ensureCapacity(dataJsonArr.length());
return null;
}
}
}
@SuppressLint("NewApi") public int getScreenWidth() {
int columnWidth;
WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
Display display = wm.getDefaultDisplay();
final Point point = new Point();
try {
display.getSize(point);
} catch (java.lang.NoSuchMethodError ignore) {
point.x = display.getWidth();
point.y = display.getHeight();
}
columnWidth = point.x;
return columnWidth;
}
}
最后我的GridViewImageAdapter类：
public class GridViewImageAdapter extends BaseAdapter{
private Context context;
private int imageWidth;
private ArrayList<HashMap<String, String>> galleryAttributes;
ImageView imageView;
public GridViewImageAdapter(Context context, ArrayList<HashMap<String, String>> galleryAttributes, int imageWidth){
this.galleryAttributes = galleryAttributes;
this.context = context;
this.imageWidth = imageWidth;
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return galleryAttributes.size();
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return galleryAttributes.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
imageView = new ImageView(context);
} else {
imageView = (ImageView) convertView;
}
Picasso.with(context).load(galleryAttributes.get(position).get("Link")).placeholder(R.drawable.loadingimage).into(imageView);
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setLayoutParams(new GridView.LayoutParams(imageWidth,imageWidth));
return imageView;
}
}