Android 最常用的设计模式九 安卓源码分析—— 适配器模式（Adapter）_安卓项目适配器源码是什么

• 目标(Target)角色：这就是所期待得到的接口。注意：由于这里讨论的是类适配器模式，因此目标不可以是类。
• 源(Adapee)角色：现在需要适配的接口。

• 适配器(Adaper)角色：适配器类是本模式的核心。适配器把源接口转换成目标接口。显然，这一角色不可以是接口，而必须是具体类。

  在上述电源接口这个示例中，5V电压就是Target接口，220v电压就是Adaptee类，而将电压从220V转换到5V就是Adapter。

  //本来是220的电压，现在用户需求转成5v的电压
  public void testAdapterMode2(){
      ObjectAdapter adapter=new ObjectAdapter(new Volt220());
      adapter.getVolt5();
  
  }

public class ObjectAdapter implements FiveVolt {

    Volt220 mVolt220;

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

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

    @Override
    public int getVolt5() {
        return 0;
    }
}

/**
 * Created by Administrator on 2017/9/15.
 * target角色
 */

public interface FiveVolt {

    public int getVolt5();
}

/**
 * Created by Administrator on 2017/9/15.
 * Adaptee角色,需要被转换的对象
 */

public class Volt220  {

    public int getVolt220() {
        return 220;
    }
}

ListView中的Adapter模式

在开发过程中,ListView的Adapter是我们最为常见的类型之一。一般的用法大致如下:

public class HottestAdapter extends BaseAdapter implements OnClickListener, DownloadManager.DownloadListener, ApkHelper.InstallListener,
        ApkHelper.UnInstallListener {


    String TAG="HottestAdapter";

    private ArrayList<LaunNearbyHotBean> list;
    private LayoutInflater inflater;
    private Context mContext;
    private DownloadManager downloadManager;
    private String mDownloadSavePath;
    private ApkHelper apkHelper2;
    private ApkInstalledManager installedManager;
//    private ExpandableListView listView;

    public HottestAdapter(ArrayList<LaunRecommendGroup> groupDatas, Context mContext) {
        list = new ArrayList<LaunNearbyHotBean>();
        for (LaunRecommendGroup group : groupDatas) {
            list.addAll(group.getApkList());
        }
        this.mContext = mContext;
        inflater = LayoutInflater.from(mContext);
        downloadManager = DownloadManager.getInstance(mContext);
        mDownloadSavePath = HJStorageUtil.getDirDownload(mContext).getAbsolutePath() + "/";
        apkHelper2 = ApkHelper.getInstance(mContext.getApplicationContext());
        apkHelper2.registListener(this);
        apkHelper2.registUninstallListener(this);
        installedManager = ApkInstalledManager.getInstance(mContext.getApplicationContext());
        EventBus.getDefault().register(this);
        mSwitchInstallPlungi=CXPolicyUtil.isShowUpdateSwitch(mContext, CXPolicyUtil.ON_HOTTEST_INSTALL_SWITCH);
        mSwitchInstallPlungi=!mSwitchInstallPlungi;

        if(PermissionUtilsO.isAndroidO()){
            mSwitchInstallPlungi=false;
        }

//        if(CXConfig.DEBUG){
//            mSwitchInstallPlungi=true;
//        }
    }

    public void destroy(){   EventBus.getDefault().unregister(this);}

    /**应用装容器还是装在系统
     * false,装系统，
     * True,装容器
     *
     * */
    private boolean mSwitchInstallPlungi=false;

    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder = null;
        if (convertView == null) {
            viewHolder = new ViewHolder();
            convertView = inflater.inflate(R.layout.launcher_recommend_item, null);
            viewHolder.ivAppIcon = (RoundImageView) convertView.findViewById(R.id.iv_appIc);
            viewHolder.tvAppName = (TextView) convertView.findViewById(R.id.tv_name);
            viewHolder.tvDownloadCount = (TextView) convertView.findViewById(R.id.tv_downNumber);
            viewHolder.tvDescription = (TextView) convertView.findViewById(R.id.tv_description);
            viewHolder.tvAppSize = (TextView) convertView.findViewById(R.id.tv_appSize);
            viewHolder.rlDownloadLayout = (RelativeLayout) convertView.findViewById(R.id.down_app);
            viewHolder.pbDownload = (ProgressBar) convertView.findViewById(R.id.child_right_progress_green);
            viewHolder.tvAppStatus = (TextView) convertView.findViewById(R.id.child_right_progress_txt);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        LaunNearbyHotBean apkModel = (LaunNearbyHotBean) getItem(position);
        apkModel.fromSource=5;
        viewHolder.position = position;
        viewHolder.key = apkModel.packageName;
        ImageLoaderUtil.loadAppIcon(viewHolder.ivAppIcon, apkModel.iconUrl);

        String showTitle=apkModel.title;

        if((Integer.valueOf(apkModel.serverApkOrg))>YYB_VALUE){
            showTitle=YYB_FLAG+showTitle;
        }

        viewHolder.tvAppName.setText(showTitle);
        viewHolder.tvDownloadCount.setText(apkModel.getDownloadCount());
        viewHolder.tvDescription.setText(apkModel.getAppDescription());
//        if(apkModel.title.equals("天猫")){
//            CXLog.e(TAG,"sizeFormat(apkModel.getSize()="+sizeFormat(apkModel.getSize())+"apkModel.getSize()=="+apkModel.getSize());
//        }
//
//        CXLog.e("FreeInstallAdapter", "model=====" + apkModel.title +
//                "packageName===" + apkModel.packageName+"apkModel.versionCode=="+apkModel.versionCode);

//        CXLog.e(TAG,"apkModelUrl=="+apkModel.downloadUrl);

        viewHolder.tvAppSize.setText(sizeFormat(apkModel.getSize()));
        setAppStatus(viewHolder, apkModel);

        viewHolder.rlDownloadLayout.setTag(viewHolder);
        viewHolder.rlDownloadLayout.setOnClickListener(this);

        return convertView;
    }

public class ListView extends AbsListView {
    /**
     * Used to indicate a no preference for a position type.
     */
    static final int NO_POSITION = -1;

    /**
     * When arrow scrolling, ListView will never scroll more than this factor
     * times the height of the list.
     */
    private static final float MAX_SCROLL_FACTOR = 0.33f;

    /**
     * When arrow scrolling, need a certain amount of pixels to preview next
     * items.  This is usually the fading edge, but if that is small enough,
     * we want to make sure we preview at least this many pixels.
     */
    private static final int MIN_SCROLL_PREVIEW_PIXELS = 2;

    /**
     * A class that represents a fixed view in a list, for example a header at the top
     * or a footer at the bottom.
     */
    public class FixedViewInfo {
        /** The view to add to the list */
        public View view;
        /** The data backing the view. This is returned from {@link ListAdapter#getItem(int)}. */
        public Object data;
        /** <code>true</code> if the fixed view should be selectable in the list */
        public boolean isSelectable;
    }

    private ArrayList<FixedViewInfo> mHeaderViewInfos = Lists.newArrayList();
    private ArrayList<FixedViewInfo> mFooterViewInfos = Lists.newArrayList();

    Drawable mDivider;
    int mDividerHeight;

    Drawable mOverScrollHeader;
    Drawable mOverScrollFooter;

    private boolean mIsCacheColorOpaque;
    private boolean mDividerIsOpaque;

    private boolean mHeaderDividersEnabled;
    private boolean mFooterDividersEnabled;

    private boolean mAreAllItemsSelectable = true;

    private boolean mItemsCanFocus = false;

    // used for temporary calculations.
    private final Rect mTempRect = new Rect();
    private Paint mDividerPaint;

    // the single allocated result per list view; kinda cheesey but avoids
    // allocating these thingies too often.
    private final ArrowScrollFocusResult mArrowScrollFocusResult = new ArrowScrollFocusResult();

    // Keeps focused children visible through resizes
    private FocusSelector mFocusSelector;

    public ListView(Context context) {
        this(context, null);
    }

    public ListView(Context context, AttributeSet attrs) {
        this(context, attrs, R.attr.listViewStyle);
    }

    public ListView(Context context, AttributeSet attrs, int defStyleAttr) {
        this(context, attrs, defStyleAttr, 0);
    }

View obtainView(int position, boolean[] isScrap) {
    Trace.traceBegin(Trace.TRACE_TAG_VIEW, "obtainView");

    isScrap[0] = false;

    // Check whether we have a transient state view. Attempt to re-bind the
    // data and discard the view if we fail.
    final View transientView = mRecycler.getTransientStateView(position);
    if (transientView != null) {
        final LayoutParams params = (LayoutParams) transientView.getLayoutParams();

        // If the view type hasn't changed, attempt to re-bind the data.
        if (params.viewType == mAdapter.getItemViewType(position)) {
            final View updatedView = mAdapter.getView(position, transientView, this);

            // If we failed to re-bind the data, scrap the obtained view.
            if (updatedView != transientView) {
                setItemViewLayoutParams(updatedView, position);
                mRecycler.addScrapView(updatedView, position);
            }
        }

        isScrap[0] = true;

        // Finish the temporary detach started in addScrapView().
        transientView.dispatchFinishTemporaryDetach();
        return transientView;
    }

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


    if (!mDataChanged) {
        // Try to use an existing view for this position
        child = mRecycler.getActiveView(position);
        if (child != null) {
            // Found it -- we're using an existing child
            // This just needs to be positioned
            setupChild(child, position, y, flow, childrenLeft, selected, true);

            return child;
        }
    }

    // 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;
}

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++;
    }

    setVisibleRangeHint(mFirstPosition, mFirstPosition + getChildCount() - 1);
    return selectedView;
}

 @Override

protected void onAttachedToWindow() {
    super.onAttachedToWindow();

    final ViewTreeObserver treeObserver = getViewTreeObserver();
    treeObserver.addOnTouchModeChangeListener(this);
    if (mTextFilterEnabled && mPopup != null && !mGlobalLayoutListenerAddedFilter) {
        treeObserver.addOnGlobalLayoutListener(this);
    }

    if (mAdapter != null && mDataSetObserver == null) {
        mDataSetObserver = new AdapterDataSetObserver();
        mAdapter.registerDataSetObserver(mDataSetObserver);

        // Data may have changed while we were detached. Refresh.
        mDataChanged = true;
        mOldItemCount = mItemCount;
        mItemCount = mAdapter.getCount();
    }
}

    ListView覆写了AbsListView中的layoutChilden函数，在该函数中根据布局模式来布局Item View。Item View的个数、样式都通过Adapter对应的方法来获取，获取个数、Item View之后，将这些Item View布局到ListView对应的坐标上，再加上Item View的复用机制，整个ListView就基本运转起来了。

当然这里的Adapter并不是经典的适配器模式，但是却是对象适配器模式的优秀示例，也很好的体现了面向对象的一些基本原则。这里的Target角色和Adapter角色融合在一起，Adapter中的方法就是目标方法；而Adaptee角色就是ListView的数据集与Item View，Adapter代理数据集，从而获取到数据集的个数、元素。

通过增加Adapter一层来将Item View的操作抽象起来，ListView等集合视图通过Adapter对象获得Item的个数、数据元素、Item View等，从而达到适配各种数据、各种Item视图的效果。因为Item View和数据类型千变万化，Android的架构师们将这些变化的部分交给用户来处理，通过getCount、getItem、getView等几个方法抽象出来，也就是将Item View的构造过程交给用户来处理，灵活地运用了适配器模式，达到了无限适配、拥抱变化的目的。