Android利用HorizontalScrollView仿ViewPager设计简单相册

最近学习了一个视频公开课，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。此篇文章参考：Android自定义HorizontalScrollView打造超强Gallery效果（这篇文章与公开课的讲的大致一样）

这里简单说一下ViewPager的缓存机制

1.进入ViewPager时，加载当前页和后一页；

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。

其实就是默认加载3页，当前页，前一页和后一页。

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。

话不多说，上代码：

代码结构如下图：

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~

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 implements
    OnClickListener {
  private LinearLayout mContainer;// MyHorizontalScrollView中的LinearLayout
  private 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index
  private int mdisplayLastIndex;// 当前显示的最后一张的index
  private int mAllFirstIndex;// 当前的第一张index 

  private 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item
      mdisplayLastIndex = 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));
  } 

  @Override
  public 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0
    scrollTo(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();
      }
    }
  } 

  @Override
  public 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)); 

  @Override
  protected 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() { 

      @Override
      public void onCurrentImgChanged(int position, View view) {
        mImg.setImageResource(mDatas.get(position));
        view.setBackgroundColor(Color.parseColor("#6d9eeb"));
      }
    });
    mHorizontalScrollView.setmOnClickImageListener(new OnClickImageChangeListener() { 

      @Override
      public 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）：

源码下载：HorizontalScrollView仿ViewPager设计相册

以上就是本文的全部内容，希望对大家学习Android软件编程有所帮助。