Android设计模式之适配器(Adapter)模式

 /**
 * Target角色
 */
public interface FiveVolt {
  public int getVolt5();
}

/**
 * Adaptee角色,需要被转换的对象
 */
public class Volt220 {
  public int getVolt220() {
    return 220;
  }
}

// adapter角色
public class ClassAdapter extends Volt220 implements FiveVolt {

  @Override
  public int getVolt5() {
    return 5;
  }

}

public class Test {
  public static void main(String[] args) {
    ClassAdapter adapter = new ClassAdapter();
    System.out.println("输出电压 : " + adapter.getVolt5());
  }
}

/**
 * Target角色
 */
public interface FiveVolt {
  public int getVolt5();
}

/**
 * Adaptee角色,需要被转换的对象
 */
public class Volt220 {
  public int getVolt220() {
    return 220;
  }
}

// 对象适配器模式
public class ObjectAdapter implements FiveVolt {

  Volt220 mVolt220;

  public ObjectAdapter(Volt220 adaptee) {
    mVolt220 = adaptee;
  }

  public int getVolt220() {
    return mVolt220.getVolt220();
  }

  @Override
  public int getVolt5() {
    return 5;
  }

}

  // 适配器
public class MyAdapter extends BaseAdapter{

    private LayoutInflater mInflater;
    List<String> mDatas ;

    public MyAdapter(Context context, List<String> datas){
      this.mInflater = LayoutInflater.from(context);
      mDatas = datas ;
    }
    @Override
    public int getCount() {
      return mDatas.size();
    }

    @Override
    public String getItem(int pos) {
      return mDatas.get(pos);
    }

    @Override
    public long getItemId(int pos) {
      return pos;
    }

    // 解析、设置、缓存convertView以及相关内容
    @Override
    public View getView(int position, View convertView, ViewGroup parent) { 
      ViewHolder holder = null;
      // Item View的复用
      if (convertView == null) {
        holder = new ViewHolder(); 
        convertView = mInflater.inflate(R.layout.my_listview_item, null);
        // 获取title
        holder.title = (TextView)convertView.findViewById(R.id.title);
        convertView.setTag(holder);
      } else {
        holder = (ViewHolder)convertView.getTag();
      }
      holder.title.setText(mDatas.get(position));
      return convertView;
    }

  }

public abstract class AbsListView extends AdapterView<ListAdapter> implements TextWatcher,
    ViewTreeObserver.OnGlobalLayoutListener, Filter.FilterListener,
    ViewTreeObserver.OnTouchModeChangeListener,
    RemoteViewsAdapter.RemoteAdapterConnectionCallback {

  ListAdapter mAdapter ;

  // 关联到Window时调用的函数
  @Override
  protected void onAttachedToWindow() {
    super.onAttachedToWindow();
    // 代码省略
    // 给适配器注册一个观察者,该模式下一篇介绍。
    if (mAdapter != null && mDataSetObserver == null) {
      mDataSetObserver = new AdapterDataSetObserver();
      mAdapter.registerDataSetObserver(mDataSetObserver);

      // Data may have changed while we were detached. Refresh.
      mDataChanged = true;
      mOldItemCount = mItemCount
      // 获取Item的数量,调用的是mAdapter的getCount方法
      mItemCount = mAdapter.getCount();
    }
    mIsAttached = true;
  }

 　/**
   * 子类需要覆写layoutChildren()函数来布局child view,也就是Item View
   */
  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
    super.onLayout(changed, l, t, r, b);
    mInLayout = true;
    if (changed) {
      int childCount = getChildCount();
      for (int i = 0; i < childCount; i++) {
        getChildAt(i).forceLayout();
      }
      mRecycler.markChildrenDirty();
    }

    if (mFastScroller != null && mItemCount != mOldItemCount) {
      mFastScroller.onItemCountChanged(mOldItemCount, mItemCount);
    }
    // 布局Child View
    layoutChildren();
    mInLayout = false;

    mOverscrollMax = (b - t) / OVERSCROLL_LIMIT_DIVISOR;
  }

  // 获取一个Item View
  View obtainView(int position, boolean[] isScrap) {
    isScrap[0] = false;
    View scrapView;
    // 从缓存的Item View中获取,ListView的复用机制就在这里
    scrapView = mRecycler.getScrapView(position);

    View child;
    if (scrapView != null) {
      // 代码省略
      child = mAdapter.getView(position, scrapView, this);
      // 代码省略
    } else {
      child = mAdapter.getView(position, null, this);
      // 代码省略
    }

    return child;
  }
 }

  @Override
  protected void layoutChildren() {
    // 代码省略

    try {
      super.layoutChildren();
      invalidate();
      // 代码省略
      // 根据布局模式来布局Item View
      switch (mLayoutMode) {
      case LAYOUT_SET_SELECTION:
        if (newSel != null) {
          sel = fillFromSelection(newSel.getTop(), childrenTop, childrenBottom);
        } else {
          sel = fillFromMiddle(childrenTop, childrenBottom);
        }
        break;
      case LAYOUT_SYNC:
        sel = fillSpecific(mSyncPosition, mSpecificTop);
        break;
      case LAYOUT_FORCE_BOTTOM:
        sel = fillUp(mItemCount - 1, childrenBottom);
        adjustViewsUpOrDown();
        break;
      case LAYOUT_FORCE_TOP:
        mFirstPosition = 0;
        sel = fillFromTop(childrenTop);
        adjustViewsUpOrDown();
        break;
      case LAYOUT_SPECIFIC:
        sel = fillSpecific(reconcileSelectedPosition(), mSpecificTop);
        break;
      case LAYOUT_MOVE_SELECTION:
        sel = moveSelection(oldSel, newSel, delta, childrenTop, childrenBottom);
        break;
      default:
        // 代码省略
        break;
      }

  }

  // 从上到下填充Item View [ 只是其中一种填充方式 ]
  private View fillDown(int pos, int nextTop) {
    View selectedView = null;

    int end = (mBottom - mTop);
    if ((mGroupFlags & CLIP_TO_PADDING_MASK) == CLIP_TO_PADDING_MASK) {
      end -= mListPadding.bottom;
    }

    while (nextTop < end && pos < mItemCount) {
      // is this the selected item?
      boolean selected = pos == mSelectedPosition;
      View child = makeAndAddView(pos, nextTop, true, mListPadding.left, selected);

      nextTop = child.getBottom() + mDividerHeight;
      if (selected) {
        selectedView = child;
      }
      pos++;
    }

    return selectedView;
  }

  // 添加Item View
  private View makeAndAddView(int position, int y, boolean flow, int childrenLeft,
      boolean selected) {
    View child;

    // 代码省略 
    // Make a new view for this position, or convert an unused view if possible
    child = obtainView(position, mIsScrap);

    // This needs to be positioned and measured
    setupChild(child, position, y, flow, childrenLeft, selected, mIsScrap[0]);

    return child;
  }