android 自定义gallerey并实现预览功能详解手机开发

自从Gallery被谷歌废弃以后，Google推荐使用ViewPager和HorizontalScrollView来实现Gallery的效果。的确HorizontalScrollView可以实现Gallery的效果，但是HorizontalScrollView存在一个很大的问题，如果你仅是用来展示少量的图片，应该是没问题的，但是如果我希望HorizontalScrollView可以想ViewPager一样，既可以绑定数据集（动态改变图片），还能做到，不管多少图片都不会OOM（ViewPager内部一直初始化，回收，至多只保持3个View）。本篇博客首先介绍HorizontalScrollView的简单用法，然后会在此基础上进行扩展，自定义HorizontalScrollView实现我们上面提到的效果，类似一屏可以显示多个View的ViewPager，再多的图片也不怕OOM。

首先差一张图片

自定义HorizontalScrollView

思想：

1、首先根据屏幕的大小和Item的大小，计算可以一个屏幕最多可以加载多少个Item，然后加载该数量Item。

2、当用户右滑（从右向左），滑动到一定距离时，加载下一张，删除第一张

3、当用户左滑（从左向右），滑动到一定距离时，加载上一张，删除最后一张

public class MyHorizontalScrollView extends HorizontalScrollView implements         OnClickListener {      private CurrentImageChangeListener mListener;     private OnItemClickListener mOnClickListener;     private LinearLayout mContainer;     private int mChildWidth;     private int mChildHeight;     private int mCurrentIndex;     private int mFristIndex;     private HorizontalScrollViewAdapter mAdapter;     private int mCountOneScreen;     private int mScreenWitdh;     private Map<View, Integer> mViewPos = new HashMap<View, Integer>();       public MyHorizontalScrollView(Context context, AttributeSet attrs) {         super(context, attrs);         WindowManager wm = (WindowManager) context                 .getSystemService(Context.WINDOW_SERVICE);         DisplayMetrics outMetrics = new DisplayMetrics();         wm.getDefaultDisplay().getMetrics(outMetrics);         mScreenWitdh = outMetrics.widthPixels;     }      @Override     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {         super.onMeasure(widthMeasureSpec, heightMeasureSpec);         mContainer = (LinearLayout) getChildAt(0);     }      protected void loadNextImg() {         if (mCurrentIndex == mAdapter.getCount() - 1) {             return;         }         scrollTo(0, 0);         mViewPos.remove(mContainer.getChildAt(0));         mContainer.removeViewAt(0);         View view = mAdapter.getView(++mCurrentIndex, null, mContainer);         view.setOnClickListener(this);         mContainer.addView(view);         mViewPos.put(view, mCurrentIndex);         mFristIndex++;         if (mListener != null) {             notifyCurrentImgChanged();         }      }      protected void loadPreImg() {         if (mFristIndex == 0)             return;         int index = mCurrentIndex - mCountOneScreen;         if (index >= 0) {             int oldViewPos = mContainer.getChildCount() - 1;             mViewPos.remove(mContainer.getChildAt(oldViewPos));             mContainer.removeViewAt(oldViewPos);             //将此View放入第一个位置             View view = mAdapter.getView(index, null, mContainer);             mViewPos.put(view, index);             mContainer.addView(view, 0);             view.setOnClickListener(this);             //水平滚动位置向左移动view的宽度个像素             scrollTo(mChildWidth, 0);             //当前位置--，当前第一个显示的下标--             mCurrentIndex--;             mFristIndex--;             if (mListener != null) {                 notifyCurrentImgChanged();              }         }     }      //更改当前背景色     public void notifyCurrentImgChanged() {         for (int i = 0; i < mContainer.getChildCount(); i++) {             mContainer.getChildAt(i).setBackgroundColor(Color.WHITE);         }         mListener.onCurrentImgChanged(mFristIndex, mContainer.getChildAt(0));     }      public void setDatas(HorizontalScrollViewAdapter mAdapter) {         this.mAdapter = mAdapter;         mContainer = (LinearLayout) getChildAt(0);         final View view = mAdapter.getView(0, null, mContainer);         mContainer.addView(view);         if (mChildWidth == 0 && mChildHeight == 0) {             int w = MeasureSpec.makeMeasureSpec(0,                     MeasureSpec.UNSPECIFIED);             int h = MeasureSpec.makeMeasureSpec(0,                     MeasureSpec.UNSPECIFIED);             view.measure(w, h);             mChildHeight = view.getMeasuredHeight();             mChildWidth = view.getMeasuredWidth();             mChildHeight = view.getMeasuredHeight();             mCountOneScreen = (mScreenWitdh / mChildWidth == 0) ? mScreenWitdh / mChildWidth + 1 : mScreenWitdh / mChildWidth + 2;         }         initFirstScreenChildren(mCountOneScreen);     }      public void initFirstScreenChildren(int mCountOneScreen) {         mContainer = (LinearLayout) getChildAt(0);         mContainer.removeAllViews();         mViewPos.clear();          for (int i = 0; i < mCountOneScreen; i++) {             View view = mAdapter.getView(i, null, mContainer);             view.setOnClickListener(this);             mContainer.addView(view);             mViewPos.put(view, i);             mCurrentIndex = i;         }         if (mListener != null) {             notifyCurrentImgChanged();         }      }      @Override     public boolean onTouchEvent(MotionEvent ev) {         switch (ev.getAction()) {             case MotionEvent.ACTION_MOVE:                 int scrollX = getScrollX();                 // 如果当前scrollX为view的宽度，加载下一张，移除第一张                 if (scrollX >= mChildWidth) {                     loadNextImg();                 }                 // 如果当前scrollX = 0， 往前设置一张，移除最后一张                 if (scrollX == 0) {                     loadPreImg();                 }                 break;         }         return super.onTouchEvent(ev);     }      @Override     public void onClick(View v) {         if (mOnClickListener != null) {             for (int i = 0; i < mContainer.getChildCount(); i++) {                 mContainer.getChildAt(i).setBackgroundColor(Color.WHITE);             }             mOnClickListener.onClick(v, mViewPos.get(v));         }     }      public void setOnItemClickListener(OnItemClickListener mOnClickListener) {         this.mOnClickListener = mOnClickListener;     }      public void setCurrentImageChangeListener(             CurrentImageChangeListener mListener) {         this.mListener = mListener;     }       public interface CurrentImageChangeListener {         void onCurrentImgChanged(int position, View viewIndicator);     }      public interface OnItemClickListener {         void onClick(View view, int pos);     } }

接下来我们写一个Adapter用来填充界面，然后在我们首页组装下数据，设置下适配器就好了，是不是很简单。

public class HorizontalScrollViewAdapter extends BaseAdapter{      private Context mContext;     private LayoutInflater mInflater;     private List<GalleryModel> mDatas;      public HorizontalScrollViewAdapter(Context context, List<GalleryModel> mDatas) {         this.mContext = context;         mInflater = LayoutInflater.from(context);         this.mDatas = mDatas;     }      public int getCount() {         return mDatas.size();     }      public Object getItem(int position) {         return mDatas.get(position);     }      public long getItemId(int position) {         return position;     }      public View getView(int position, View convertView, ViewGroup parent) {         ViewHolder viewHolder = null;         if (convertView == null) {             convertView = mInflater.inflate(                     R.layout.activity_gallery_item, parent, false);             viewHolder = new ViewHolder(convertView);         } else {             viewHolder = (ViewHolder) convertView.getTag();         }          initItem(viewHolder,position);         return convertView;     }      private void initItem(ViewHolder viewHolder, int position) {         viewHolder.itemImage.setImageResource(mDatas.get(position).image);         viewHolder.itemText.setText(mDatas.get(position).name);     }       class ViewHolder {         @Bind(R.id.item_image)         ImageView itemImage;         @Bind(R.id.item_text)         TextView itemText;          public ViewHolder(View parent) {             ButterKnife.bind(this, parent);             parent.setTag(this);         }     }  }

有兴趣的可以下载代码：

https://github.com/xiangzhihong/gallery