android GridView 在TV上，上下翻页的时候平滑滑动的实现

应该做过android tv开发的同学都知道，在TV上使用GridView的时候，如果焦点上下移动的时候，如果移动到在屏幕上可见的第一行或者最后一行的时候，如果再继续上下移动，

的话，是比较生硬呆滞的的上下滚动页面，焦点移动到下一个item上，这是非常不太好的体验效果，我们要的是比较平滑的滚动效果。

首先我们要来了解一下GridView的如下这个方法:

smoothScrollToPositionFromTop(int position,int offset,int duration);

滚动到position项目的位置，并且position项目距离GirdView上边的距离为offset个像素，duration指定滚动需要的时间（毫秒）。

这个方法是今天的主角，虽然是主角，但不是说只有使用这个方法就可以了？当然不是，当然也需要一定的逻辑算法配合。

今天就说说我是如何实现的。

先说说我的思路：

首先你要知道当前item所在的行，才知道按上下按键的时候，要滚动到哪一个postion。

public class AppsGridViewAdapter extends BaseAdapter {private int mCurrentSelectedPosition = 0;private int mLastSelectedPosition = 0;private static final int ITEM_BG_COLORS[] = new int[]{Color.parseColor("#e0c101"),Color.parseColor("#fbaf54"),Color.parseColor("#684cb5"),Color.parseColor("#23a5ba"),Color.parseColor("#03ba9f"),Color.parseColor("#88c04c"),Color.parseColor("#684cb5"),Color.parseColor("#23a5ba"),Color.parseColor("#03ba9f"),Color.parseColor("#88c04c"),Color.parseColor("#e0c101"),Color.parseColor("#fbaf54"),};private int mColorIndex = 0;private List<AppInfo> mApps = new ArrayList<AppInfo>();private Context mContext;private int mGridViewRows = 0;public AppsGridViewAdapter(Context context, List<AppInfo> apps) {this.mContext = context;if(apps!=null)this.mApps = apps;setRows();mColorIndex = 0;}private void setRows() {int remainder = mApps.size() % 6;mGridViewRows =(remainder == 0)? (this.mApps.size() > 0 ?  this.mApps.size() / 6:0) : (mApps.size() / 6) +1;}public int getNumRows() {return mGridViewRows;}public int getNumColumns(){return 6;}@Overridepublic void notifyDataSetChanged() {mColorIndex = 0;super.notifyDataSetChanged();}public void setApps(List<AppInfo> apps){mApps.clear();if(apps!=null)mApps = apps;setRows();}public void addApp(AppInfo app){if(app!=null && app.isValidate())mApps.add(app);setRows();}public void removeApp(AppInfo app){if(app!=null)mApps.remove(app);setRows();}public int getCurrentSelectedPosition() {return mCurrentSelectedPosition;}public int getLastSelectedPosition() {return mLastSelectedPosition;}@Overridepublic int getCount() {return mApps.size();}@Overridepublic Object getItem(int position) {return mApps.get(position);}@Overridepublic long getItemId(int position) {return position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {ViewHolder holder = null;if(convertView == null){ convertView = View.inflate(mContext, R.layout.apps_page_gridview_item_layout, null); holder = new ViewHolder(); holder.mAppIcon = (ImageView) convertView.findViewById(R.id.app_icon); holder.mAppName = (TextView) convertView.findViewById(R.id.app_name); holder.mAppIconColorBg = (RelativeLayout) convertView.findViewById(R.id.app_icon_color_bg); convertView.setTag(holder);}holder = (ViewHolder) convertView.getTag();holder.mAppName.setText(mApps.get(position).getName());holder.mAppIcon.setBackgroundDrawable(mApps.get(position).getIcon());holder.mAppIconColorBg.setBackgroundColor(ITEM_BG_COLORS[mColorIndex]);++mColorIndex;mColorIndex =( (mColorIndex / 6) != 0 && (mColorIndex / 6) % 2 == 0 ) ? 0 :mColorIndex;return convertView;}private static final class ViewHolder{private ImageView mAppIcon;private TextView mAppName;private RelativeLayout mAppIconColorBg;}}

我们看到，Adapter中定一个了两个方法，可以用来获取多少行，和多少列(列一般是已知的)。

setRows() ;是每次设置给adapter数据的时候，都重新弄设置一下总行数。

getNumRows，返回获取当前所有的行数，getNumColumns返回所有的列数。

OK，接下来，我们就可以通过postion来算出当前选中的postion在哪一行了。

package net.sunniwell.projector.luncher.page;import java.util.List;import net.sunniwell.projector.luncher.CategoryPageActivity;import net.sunniwell.projector.luncher.R;import net.sunniwell.projector.luncher.adapter.AppsGridViewAdapter;import net.sunniwell.projector.luncher.bean.AppInfo;import net.sunniwell.projector.luncher.engine.PackageAsyncTask;import net.sunniwell.projector.luncher.engine.PackageAsyncTask.OnQueryPackageStateListener;import net.sunniwell.projector.luncher.engine.PackageEngine;import net.sunniwell.projector.luncher.engine.PackageEngine.OnPackageStateChangeListener;import net.sunniwell.projector.luncher.views.CommonGridView;import android.content.Intent;import android.view.View;import android.view.ViewGroup;import android.widget.AdapterView;import android.widget.AdapterView.OnItemClickListener;import android.widget.AdapterView.OnItemSelectedListener;import android.widget.TextView;/** *  * @author zhanghuagang 2017.7.6 * */public class AppsPage extends BasePage implements OnPackageStateChangeListener, OnItemSelectedListener,OnQueryPackageStateListener ,OnItemClickListener{static{sCategory = 3;}private int mCurrentRow = 0;private TextView mIndexTextView;private CommonGridView mGridView;private AppsGridViewAdapter mAppsAdapter;private PackageAsyncTask mAsyncTask;private PackageEngine mPackageEngine;public AppsPage(CategoryPageActivity activity, ViewGroup contentView,int category) {super(activity, contentView, category);this.mPackageEngine = PackageEngine.getDefault(activity);this.mPackageEngine.setOnPackageStateChangeListener(this);}@Overridepublic void initView() {mIndexTextView = (TextView) mContentView.findViewById(R.id.index_textview);mGridView = (CommonGridView) mContentView.findViewById(R.id.apps_gridview);mGridView.setOnItemSelectedListener(this);mGridView.setOnItemClickListener(this);mAppsAdapter = new AppsGridViewAdapter(mActivity,null);mGridView.setAdapter(mAppsAdapter);mAppsAdapter.notifyDataSetChanged();}@Overridepublic void onResume() {mPackageEngine.register();queryApps();}private void queryApps() {if(mAsyncTask!=null)mAsyncTask.stop();mAsyncTask = new PackageAsyncTask(mActivity, this);mAsyncTask.start();}@Overridepublic void onStop() {}@Overridepublic void onPause() {mPackageEngine.unregister();}@Overridepublic void onDestroy() {}private int getItemIndex(int position){int r = position % mAppsAdapter.getNumColumns() ;if(r  == 0){ if(position > 0 ){  return (position/mAppsAdapter.getNumColumns())+1; }else{ return 1; }}else{    return (position/mAppsAdapter.getNumColumns())+1;}}@Overridepublic void onItemSelected(AdapterView<?> parent, View view, int position,long id) {if(getItemIndex(position) > mCurrentRow){mGridView.smoothScrollToPositionFromTop(position, 0,500);}else if(getItemIndex(position) < mCurrentRow){mGridView.smoothScrollToPositionFromTop(position-2, 0,500);}mGridView.onItemSelected(parent, view, position, id);mIndexTextView.setText(getItemIndex(position)+"  |  "+mAppsAdapter.getNumRows());mCurrentRow =getItemIndex(position); }@Overridepublic void onNothingSelected(AdapterView<?> parent) {}@Overridepublic void onFinish(List<AppInfo> apps) {mAppsAdapter.setApps(apps);mAppsAdapter.notifyDataSetChanged();}@Overridepublic void onItemClick(AdapterView<?> parent, View view, int position,long id) {AppInfo app = (AppInfo) mAppsAdapter.getItem(position);if(app!=null){final Intent intent = new Intent();intent.setClassName(app.packageName, app.className);intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);mActivity.startActivity(intent);}}@Overridepublic void onPackageAdded(AppInfo app) {mAppsAdapter.addApp(app);mAppsAdapter.notifyDataSetChanged();}@Overridepublic void onPackageDeleted(AppInfo app) {mAppsAdapter.removeApp(app);mAppsAdapter.notifyDataSetChanged();}}

我的getItemIndex(int postion)就是根据position获取当前所在行的。

然后我们在onItemSelected对平滑滑动做处理。

如果下一个获取焦点的item所在行小于当前行，说明是向上按的，如果是大于当前行，说明是向下按住的。

这里我们特殊的处理的向下按的，position-2，这个意思就是当我向下按的时候，每次移动两个postion的距离，并且postion和边缘距离为0