仿ViewPager相册（使用HorizontalScrollView）

本文主要是介绍仿ViewPager相册（使用HorizontalScrollView），希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

</pre>      <p></p><p>       近期看了一堂某在线IT学习的视频公开课，这里就不说名字了，省的有打广告的嫌疑。讲到了利用HorizontalScrollView仿ViewPager设计的一个简单相册。其实主要用了ViewPager缓存的思想。此篇博客参考<a target=_blank target="_blank" href="http://blog.csdn.net/lmj623565791/article/details/38140505" style="text-decoration:none; color:rgb(12,137,207); font-family:'microsoft yahei'; font-size:15px; line-height:35px">http://blog.csdn.net/lmj623565791/article/details/38140505</a>（这篇博客与公开课的讲的大致一样）</p><p>       这里简单说一下ViewPager的缓存机制</p><p>       1.进入ViewPager时，加载当前页和后一页；</p><p>       2.当滑动ViewPager至下一页时，加载后一页，此时第一页是不会销毁的，同时加载当前页的下一页。</p><p>其实就是默认加载3页，当前页，前一页和后一页。</p><p>       而此HorizontalScrollView是默认加载两页的，这个要注意，不然调度代码会让人晕。</p><p>       话不多说，上代码：</p><p>       代码结构如下图：<img src="https://img-blog.csdn.net/20160521161649394?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" /></p><p>       一个View，一个Adapter，一个MainActivity，相信不用解释，大家也相当清楚了，典型的MVC模式~</p><p></p><pre code_snippet_id="1691658" snippet_file_name="blog_20160521_2_7131836" name="code" class="java">package com.ssa.horizontalscrollview.myview;import java.util.HashMap;
import java.util.Map;import com.ssa.horizontalscrollview.myUtils.DisplayUtil;import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.HorizontalScrollView;
import android.widget.LinearLayout;public class GalleryHorizontalScrollView extends HorizontalScrollView implementsOnClickListener {private LinearLayout mContainer;// MyHorizontalScrollView中的LinearLayoutprivate int mChildWidth;// 子元素的宽度private int mChildHeight;// 子元素的高度private int mAllLastIndex;// 当前的最后一张的indexprivate int mdisplayLastIndex;// 当前显示的最后一张的indexprivate int mAllFirstIndex;// 当前的第一张indexprivate GalleryHorizontalScrollViewAdapter mAdapter;// 数据适配器private int mScreenWidth;// 屏幕的宽度private int mCountOneScreen;private Map<View, Integer> mViewPos = new HashMap<View, Integer>();private OnCurrentImageChangeListener mOnCurrentImageChangeListener;private OnClickImageChangeListener mOnClickImageChangeListener;public void setmOnCurrentImageChangeListener(OnCurrentImageChangeListener mListener) {this.mOnCurrentImageChangeListener = mListener;}public void setmOnClickImageListener(OnClickImageChangeListener mListener) {this.mOnClickImageChangeListener = mListener;}/*** 图片滚动时回调接口*/public interface OnCurrentImageChangeListener {void onCurrentImgChanged(int position, View view);}/*** 点击图片时回调接口*/public interface OnClickImageChangeListener {void onClickImageChangeListener(int position, View view);}public GalleryHorizontalScrollView(Context context, AttributeSet attrs) {super(context, attrs);// 获取屏幕宽度mScreenWidth = getResources().getDisplayMetrics().widthPixels;}/*** 初始化数据，设置适配器*/public void initData(GalleryHorizontalScrollViewAdapter mAdapter) {this.mAdapter = mAdapter;mContainer = (LinearLayout) getChildAt(0);final View view = mAdapter.getView(0, null, mContainer);mContainer.addView(view);if (mChildHeight == 0 && mChildWidth == 0) {/*int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);*//*** 上面注释掉的是一位老师的写法，但我查了好多资料，用参数0和View.MeasureSpec.UNSPECIFIED是一种不太优美的做法；* 好的做法应该是* 当View为match_parent时，无法测量出View的大小（任玉刚大神讲的，确实是这么一回事,这个具体的原因要结合源码分析，可以看一下任大神的博客）* 当View宽高为具体的数值时，比如100px：* int w =View.MeasureSpec.makeMeasureSpec(100, View.MeasureSpec.EXACTLY);* int h =View.MeasureSpec.makeMeasureSpec(100, View.MeasureSpec.EXACTLY);* view.measure(w, h);* 当View宽高为wrap_content时：* int w =View.MeasureSpec.makeMeasureSpec((1<<30)-1, View.MeasureSpec.AT_MOST);* int h =View.MeasureSpec.makeMeasureSpec((1<<30)-1, View.MeasureSpec.AT_MOST);* view.measure(w, h);* * 我的此View高度为固定的150dip,宽度为wrap_content*/int heightPx = DisplayUtil.dip2px(getContext(), 150);int w =View.MeasureSpec.makeMeasureSpec((1<<30)-1, View.MeasureSpec.AT_MOST);int h =View.MeasureSpec.makeMeasureSpec(heightPx, View.MeasureSpec.EXACTLY);view.measure(w, h);mChildHeight = view.getMeasuredHeight();mChildWidth = view.getMeasuredWidth();// 计算每次加载多少个itemmdisplayLastIndex = mScreenWidth / mChildWidth;mCountOneScreen = mdisplayLastIndex + 1;initFirstScreenChildren(mdisplayLastIndex + 1);}}/*** 加载第一屏的元素* * @param mDisplayCountOneScreen*/private void initFirstScreenChildren(int mDisplayCountOneScreen) {mContainer = (LinearLayout) getChildAt(0);mContainer.removeAllViews();mViewPos.clear();for (int i = 0; i < mDisplayCountOneScreen; i++) {View view = mAdapter.getView(i, null, mContainer);// 待完善的点击事件view.setOnClickListener(this);mContainer.addView(view);mViewPos.put(view, i);mAllLastIndex = i;}// 初始化并刷新界面if (null != mOnCurrentImageChangeListener) {notifyCurrentImgChanged();}}private void notifyCurrentImgChanged() {// 先清除所有的背景颜色，点击时设置为蓝色for (int i = 0; i < mContainer.getChildCount(); i++) {mContainer.getChildAt(i).setBackgroundColor(Color.WHITE);}mOnCurrentImageChangeListener.onCurrentImgChanged(mAllFirstIndex,mContainer.getChildAt(0));}@Overridepublic boolean onTouchEvent(MotionEvent ev) {/** Log.e("X", getX()+""); Log.e("ChildX",* mContainer.getChildAt(0).getX()+""); Log.e("RawX",getLeft() +"");*/switch (ev.getAction()) {case MotionEvent.ACTION_MOVE:int scrollX = getScrollX();Log.e("ScrollX", scrollX + "");if (scrollX >= mChildWidth) {// 加载下一页，移除第一张loadNextImg();}if (scrollX == 0) {// 加载上一页，移除最后一张loadPreImg();}break;}return super.onTouchEvent(ev);}private void loadNextImg() {// 数组边界值计算if (mAllLastIndex == mAdapter.getCount() - 1) {return;}// 移除第一张图片，且将水平滚动位置置0scrollTo(0, 0);mViewPos.remove(mContainer.getChildAt(0));mContainer.removeViewAt(0);// 获取下一张图片，并且设置onclick事件，且加入容器中View view = mAdapter.getView(++mAllLastIndex, null, mContainer);view.setOnClickListener(this);mContainer.addView(view);mViewPos.put(view, mAllLastIndex);// 当前第一张图片小标mAllFirstIndex++;// 如果设置了滚动监听则触发if (mOnCurrentImageChangeListener != null) {notifyCurrentImgChanged();}}private void loadPreImg() {if (mAllFirstIndex == 0) {return;}int index = mAllLastIndex - mCountOneScreen;if (index >= 0) {// 移除最后一张int oldViewPos = mContainer.getChildCount() - 1;mViewPos.remove(mContainer.getChildAt(oldViewPos));mContainer.removeViewAt(oldViewPos);// 将加入的View放在第一个位置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的宽度的像素scrollTo(mChildWidth, 0);mAllLastIndex--;mAllFirstIndex--;if (null != mOnCurrentImageChangeListener) {notifyCurrentImgChanged();}}}@Overridepublic void onClick(View v) {if(null!=mOnClickImageChangeListener){mOnClickImageChangeListener.onClickImageChangeListener(mViewPos.get(v), v);}}
}

下面是Adapter的源码：

package com.ssa.horizontalscrollview.myview;import java.util.List;import com.ssa.horizontalscrollview.R;import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;public class GalleryHorizontalScrollViewAdapter {private LayoutInflater mInflater;private List<Integer> mDatas;public GalleryHorizontalScrollViewAdapter(Context context, List<Integer> mDatas) {mInflater = LayoutInflater.from(context);this.mDatas = mDatas;}public Object getItem(int position) {return mDatas.get(position);}public long getItemId(int position) {return position;}public int getCount() {return mDatas.size();}public View getView(int position, View contentView, ViewGroup parent) {ViewHolder myHolder = null;if (null == contentView) {contentView = mInflater.inflate(R.layout.activity_gallery_item,parent, false);myHolder = new ViewHolder(contentView);contentView.setTag(myHolder);}else {myHolder = (ViewHolder)contentView.getTag();}myHolder.ivImg.setImageResource(mDatas.get(position));myHolder.tvText.setText("Img_"+position);return contentView;}private static class ViewHolder {ImageView ivImg;TextView tvText;public ViewHolder(View view) {ivImg = (ImageView)view.findViewById(R.id.iv_content);tvText =(TextView)view.findViewById(R.id.tv_index);}}}

下面是MainActivity的源码：

package com.ssa.horizontalscrollview;import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;import com.ssa.horizontalscrollview.myview.GalleryHorizontalScrollView;
import com.ssa.horizontalscrollview.myview.GalleryHorizontalScrollView.OnClickImageChangeListener;
import com.ssa.horizontalscrollview.myview.GalleryHorizontalScrollView.OnCurrentImageChangeListener;
import com.ssa.horizontalscrollview.myview.GalleryHorizontalScrollViewAdapter;public class MainActivity extends Activity {private GalleryHorizontalScrollView mHorizontalScrollView;private GalleryHorizontalScrollViewAdapter mAdapter;private ImageView mImg;private List<Integer> mDatas = new ArrayList<Integer>(Arrays.asList(R.drawable.a, R.drawable.b, R.drawable.c, R.drawable.d,R.drawable.e,R.drawable.f,R.drawable.g));@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mImg = (ImageView)findViewById(R.id.iv_content);mHorizontalScrollView = (GalleryHorizontalScrollView)findViewById(R.id.mhsv_gallery_container);mAdapter = new GalleryHorizontalScrollViewAdapter(this, mDatas);mHorizontalScrollView.setmOnCurrentImageChangeListener(new OnCurrentImageChangeListener() {@Overridepublic void onCurrentImgChanged(int position, View view) {mImg.setImageResource(mDatas.get(position));view.setBackgroundColor(Color.parseColor("#6d9eeb"));}});mHorizontalScrollView.setmOnClickImageListener(new OnClickImageChangeListener() {@Overridepublic void onClickImageChangeListener(int position, View view) {mImg.setImageResource(mDatas.get(position));}});mHorizontalScrollView.initData(mAdapter);}
}

至些，调试运行，读者会发现，整个相册会非常卡，

甚至有的图片还没有显示出来如img_4，看一下logcat，相信大家会发现原因：

信息已经提示的很清楚了，图片太大，

此时大家应该明白了，笔者故意选择了几张很大的图片加载，虽然没大到直接让应用崩掉，但是体验性已经变得非常差了，这是因为课堂上的老师讲课时用的图片都是几十K的小图片，加载当然不会有问题，所以要想使这个相册作为一个实用的相册，还要处理图片过大的问题，不然，依旧会造成OOM。

此时就用到这个工具类了：

package com.ssa.horizontalscrollview.myUtils;import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;public class BitmapUtil {public static Bitmap decodeSampledBitmapFromResources(Resources res,int resId, int reqWidth, int reqHeight) {final BitmapFactory.Options options = new BitmapFactory.Options();options.inJustDecodeBounds = true;BitmapFactory.decodeResource(res, resId, options);options.inSampleSize = calculateInsampleSize(options, reqWidth,reqHeight);options.inJustDecodeBounds = false;return BitmapFactory.decodeResource(res, resId, options);}public static int calculateInsampleSize(BitmapFactory.Options options,int reqWidth, int reqHeight) {final int height = options.outHeight;final int width = options.outWidth;int inSampleSize = 1;if (height > reqHeight || width > reqWidth) {final int halfHeight = height / 2;final int halfWidth = width / 2;while ((halfHeight / inSampleSize) >= reqHeight&& (halfWidth / inSampleSize) >= reqWidth) {inSampleSize *= 2;}}return inSampleSize;}
}

添加了这个工具类，上面几个类的代码也要略微修改一下，具体怎么改，大家可以下载下面我上传的源码：

至于效果如下动图所示（生成的gif图有点卡，大家可以运行看效果）：