Android利用HorizontalScrollView仿ViewPager設計簡單相冊

最近學習了一個視頻公開課，講到了利用HorizontalScrollView仿ViewPager設計的一個簡單相冊，其實主要用了ViewPager緩存的思想。此篇文章參考：Android自定義HorizontalScrollView打造超強Gallery效果（這篇文章與公開課的講的大致一樣）

 這裡簡單說一下ViewPager的緩存機制

       1.進入ViewPager時，加載當前頁和後一頁；

       2.當滑動ViewPager至下一頁時，加載後一頁，此時第一頁是不會銷毀的，同時加載當前頁的下一頁。

其實就是默認加載3頁，當前頁，前一頁和後一頁。

而此HorizontalScrollView是默認加載兩頁的，這個要注意，不然調度代碼會讓人暈。

話不多說，上代碼：

代碼結構如下圖：

一個View，一個Adapter，一個MainActivity，相信不用解釋，大家也相當清楚了，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;// 子元素的寬度 
  private int mChildHeight;// 子元素的高度 
 
  private int mAllLastIndex;// 當前的最後一張的index 
  private int mdisplayLastIndex;// 當前顯示的最後一張的index 
  private int mAllFirstIndex;// 當前的第一張index 
 
  private GalleryHorizontalScrollViewAdapter mAdapter;// 數據適配器 
  private int mScreenWidth;// 屏幕的寬度 
 
  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; 
  } 
 
  /** 
   * 圖片滾動時回調接口 
   */ 
  public interface OnCurrentImageChangeListener { 
    void onCurrentImgChanged(int position, View view); 
  } 
 
  /** 
   * 點擊圖片時回調接口 
   */ 
  public interface OnClickImageChangeListener { 
    void onClickImageChangeListener(int position, View view); 
  } 
 
  public GalleryHorizontalScrollView(Context context, AttributeSet attrs) { 
    super(context, attrs); 
    // 獲取屏幕寬度 
    mScreenWidth = getResources().getDisplayMetrics().widthPixels; 
  } 
 
  /** 
   * 初始化數據，設置適配器 
   */ 
  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);*/ 
      /** 
       * 上面注釋掉的是一位老師的寫法，但我查了好多資料，用參數0和View.MeasureSpec.UNSPECIFIED是一種不太優美的做法； 
       * 好的做法應該是 
       * 當View為match_parent時，無法測量出View的大小（任玉剛大神講的，確實是這麼一回事,這個具體的原因要結合源碼分析，可以看一下任大神的博客） 
       * 當View寬高為具體的數值時，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); 
       * 當View寬高為wrap_content時： 
       * 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高度為固定的150dip,寬度為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(); 
      // 計算每次加載多少個item 
      mdisplayLastIndex = mScreenWidth / mChildWidth; 
      mCountOneScreen = mdisplayLastIndex + 1; 
      initFirstScreenChildren(mdisplayLastIndex + 1); 
 
    } 
  } 
 
  /** 
   * 加載第一屏的元素 
   * 
   * @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); 
      // 待完善的點擊事件 
      view.setOnClickListener(this); 
      mContainer.addView(view); 
      mViewPos.put(view, i); 
      mAllLastIndex = i; 
    } 
 
    // 初始化並刷新界面 
    if (null != mOnCurrentImageChangeListener) { 
      notifyCurrentImgChanged(); 
    } 
  } 
 
  private void notifyCurrentImgChanged() { 
    // 先清除所有的背景顏色，點擊時設置為藍色 
    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) { 
        // 加載下一頁，移除第一張 
        loadNextImg(); 
      } 
      if (scrollX == 0) { 
        // 加載上一頁，移除最後一張 
        loadPreImg(); 
      } 
      break; 
    } 
 
    return super.onTouchEvent(ev); 
  } 
 
  private void loadNextImg() {// 數組邊界值計算 
    if (mAllLastIndex == mAdapter.getCount() - 1) { 
      return; 
    } 
    // 移除第一張圖片，且將水平滾動位置置0 
    scrollTo(0, 0); 
    mViewPos.remove(mContainer.getChildAt(0)); 
    mContainer.removeViewAt(0); 
 
    // 獲取下一張圖片，並且設置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); 
 
    // 當前第一張圖片小標 
    mAllFirstIndex++; 
    // 如果設置了滾動監聽則觸發 
    if (mOnCurrentImageChangeListener != null) { 
      notifyCurrentImgChanged(); 
    } 
 
  } 
 
  private void loadPreImg() { 
    if (mAllFirstIndex == 0) { 
      return; 
    } 
    int index = mAllLastIndex - mCountOneScreen; 
    if (index >= 0) { 
      // 移除最後一張 
      int oldViewPos = mContainer.getChildCount() - 1; 
      mViewPos.remove(mContainer.getChildAt(oldViewPos)); 
      mContainer.removeViewAt(oldViewPos); 
      // 將加入的View放在第一個位置 
      View view = mAdapter.getView(index, null, mContainer); 
      mViewPos.put(view, index); 
      mContainer.addView(view, 0); 
      view.setOnClickListener(this); 
      // 水平滾動位置向左移動View的寬度的像素 
      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的源碼：

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的源碼：

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，調試運行，讀者會發現，整個相冊會非常卡，

甚至有的圖片還沒有顯示出來如img_4，看一下logcat，相信大家會發現原因：

信息已經提示的很清楚了，圖片太大，

此時大家應該明白了，筆者故意選擇了幾張很大的圖片加載，雖然沒大到直接讓應用崩掉，但是體驗性已經變得非常差了，這是因為課堂上的老師講課時用的圖片都是幾十K的小圖片，加載當然不會有問題，所以要想使這個相冊作為一個實用的相冊，還要處理圖片過大的問題，不然，依舊會造成OOM。

此時就用到這個工具類了：

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; 
  } 
} 

添加了這個工具類，上面幾個類的代碼也要略微修改一下，具體怎麼改，大家可以下載下面我上傳的源碼：
至於效果如下動圖所示（生成的gif圖有點卡，大家可以運行看效果）：

源碼下載：HorizontalScrollView仿ViewPager設計相冊

以上就是本文的全部內容，希望對大家學習Android軟件編程有所幫助。