什么是裝飾設(shè)計(jì)模式姻政？

裝飾器模式是一種用于代替繼承的技術(shù)呆抑，無需通過繼承增加子類就能擴(kuò)展對象的新功能。使用對象的關(guān)聯(lián)關(guān)系代替繼承關(guān)系汁展，更加靈活鹊碍，同時避免類型體系的快速膨脹。
在不使用的繼承的方式下食绿，采用裝飾設(shè)計(jì)模式可以擴(kuò)展一個對象的功能侈咕，可以使一個對象變得越來越強(qiáng)大。

裝飾模式（Decorator）也叫包裝器模式（Wrapper）
裝飾模式降低系統(tǒng)的耦合度器紧，可以動態(tài)的增加或刪除對象的職責(zé)耀销，并使得需要裝飾的具體構(gòu)建類和具體裝飾類可以獨(dú)立變化，以便增加新的具體構(gòu)建類和具體裝飾類铲汪。

參考文章：
https://www.cnblogs.com/zhangtianq/p/6091047.html
https://blog.csdn.net/android_zyf/article/details/68343953
https://www.cnblogs.com/pecool/p/9534568.html

以普通手機(jī)和智能手機(jī)為例子來講：

Phone類：

public interface Phone {

    void call();

    void sms();
}

普通手機(jī)NormalPhone類：

public class NormalPhone implements Phone {
    @Override
    public void call() {
        System.out.println("可以打電話");
    }

    @Override
    public void sms() {
        System.out.println("可以發(fā)短信");
    }
}

智能手機(jī)SmartPhone類：

public class SmartPhone implements Phone {
    private NormalPhone mPhone;

    SmartPhone(NormalPhone phone) {
        this.mPhone = phone;
    }

    @Override
    public void call() {
        mPhone.call();
        System.out.println("打電話的同時還可以發(fā)微信熊尉、看視頻、玩游戲等等....");
    }

    @Override
    public void sms() {
        mPhone.sms();
    }
}

Client類：

public class Client {
    public static void main(String[] args) {
        NormalPhone normalPhone = new NormalPhone();
        normalPhone.call();
        System.out.println("-----------------");
        SmartPhone smartPhone = new SmartPhone(normalPhone);
        smartPhone.call();
    }
}

控制臺輸出：

可以打電話
-----------------
可以打電話
打電話的同時還可以發(fā)微信掌腰、看視頻狰住、玩游戲等等....

使用裝飾設(shè)計(jì)模式實(shí)現(xiàn)給RecyclerView添加頭部和尾部

首先要知道RecyclerView控件如何使用，可以參考下面這篇文章：
http://www.reibang.com/p/4f9591291365

MainActivity類：

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_recyclerview);

        ArrayList<String> datas = new ArrayList<>();
        for (int i = 0; i < 50; i++) {
            datas.add(" data " + i);
        }


        recyclerView = findViewById(R.id.recyclerview);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        //設(shè)置布局管理器
        recyclerView.setLayoutManager(layoutManager);
        //設(shè)置為垂直布局齿梁，這也是默認(rèn)的
        layoutManager.setOrientation(OrientationHelper.VERTICAL);
        //設(shè)置Adapter
        Adapter recycleAdapter = new Adapter(datas);


        WrapperRecyclerAdapter adapter = new WrapperRecyclerAdapter(recycleAdapter);

        recyclerView.setAdapter(adapter);

        //View headerView = LayoutInflater.from(this).inflate(R.layout.header_view, null);//todo 這樣寫效果不對
        View headerView = LayoutInflater.from(this).inflate(R.layout.header_view, recyclerView, false);
        View footerView = LayoutInflater.from(this).inflate(R.layout.footer_view, recyclerView, false);

        adapter.addHeaderView(headerView);
        adapter.addFooterView(footerView);
        //設(shè)置分隔線
        //recyclerView.addItemDecoration(new DividerGridItemDecoration(this));
        //設(shè)置增加或刪除條目的動畫
        recyclerView.setItemAnimator(new DefaultItemAnimator());

    }


}

Adapter類：

public class Adapter extends RecyclerView.Adapter<Adapter.ViewHolder> {


    private List<String> mDatas;

    public Adapter(List<String> data) {
        this.mDatas = data;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_recycler, parent, false);
        return new ViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, final int position) {

        Log.d("TAG", "onBindViewHolder:" + position);

        holder.mTextView.setText(mDatas.get(position));
        holder.mTextView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d("TAG", "onClick :" + position);
                mDatas.remove(position);
                notifyDataSetChanged();
            }
        });

    }


    @Override
    public int getItemCount() {
        return mDatas.size();
    }

    static class ViewHolder extends RecyclerView.ViewHolder {

        TextView mTextView;

        public ViewHolder(View v) {
            super(v);
            mTextView = v.findViewById(R.id.tv_title);
        }
    }
}

WrapperRecyclerAdapter類：

public class WrapperRecyclerAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private RecyclerView.Adapter mRecyclerAdapter;//原始的Adapter催植，不具有添加header和footer
    ArrayList<View> mHeaderViews;
    ArrayList<View> mFooterViews;

    public WrapperRecyclerAdapter(RecyclerView.Adapter adapter) {
        this.mRecyclerAdapter = adapter;
        mHeaderViews = new ArrayList<>();
        mFooterViews = new ArrayList<>();
        mRecyclerAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
            @Override
            public void onChanged() {
                notifyDataSetChanged();
            }
        });
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int postion) {
        Log.e("TAG", "onCreateViewHolder " + postion);
        if (postion < mHeaderViews.size()) {
            Log.e("TAG", "add header view");
            View headerView = mHeaderViews.get(postion);
            return createHeaderView(headerView);
        }

        int itemCount = mRecyclerAdapter.getItemCount();
        int adjPos = postion - mHeaderViews.size();
        if (adjPos < itemCount) {
            Log.e("TAG", "add item view");
            return mRecyclerAdapter.onCreateViewHolder(parent, mRecyclerAdapter.getItemViewType(adjPos));
        }
        Log.e("TAG", "add footer view");
        // footerview
        View footerView = mFooterViews.get(postion - itemCount - mHeaderViews.size());
        return createHeaderView(footerView);
    }

    private RecyclerView.ViewHolder createHeaderView(View view) {
        return new RecyclerView.ViewHolder(view) {
        };
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {

        Log.d("TAG", "Wrapper RecyclerAdapter onBindViewHolder:" + position);

        if (position < mHeaderViews.size()) {
            return;
        }

        int adjPos = position - mHeaderViews.size();
        if (adjPos < mRecyclerAdapter.getItemCount()) {
            mRecyclerAdapter.onBindViewHolder(holder, adjPos);
            //mRecyclerAdapter.onBindViewHolder(holder, adjPos);
        } else {
            Log.d("TAG", "adjPos getItemCount." + adjPos + "  " + mRecyclerAdapter.getItemCount());
            //fix footer view.

        }


    }

    @Override
    public int getItemViewType(int position) {
        return position;
    }

    @Override
    public int getItemCount() {
        return mRecyclerAdapter.getItemCount() + mHeaderViews.size() + mFooterViews.size();
    }

    // 添加頭部
    public void addHeaderView(View v) {
        if (!mHeaderViews.contains(v)) {
            mHeaderViews.add(v);
            notifyDataSetChanged();
        }
    }

    public void removeHeaderView(View v) {
        if (mHeaderViews.contains(v)) {
            mHeaderViews.remove(v);
            notifyDataSetChanged();
        }
    }

    // 添加尾部
    public void addFooterView(View v) {
        if (!mFooterViews.contains(v)) {
            mFooterViews.add(v);
            notifyDataSetChanged();
        }
    }

    public void removeFooterView(View v) {
        if (mFooterViews.contains(v)) {
            mFooterViews.remove(v);
            notifyDataSetChanged();
        }
    }
}

為了像ListView一樣可以直接調(diào)用addHeaderView肮蛹，我們繼承RecyclerView寫一個WrapperRecyclerView：

public class WrapperRecyclerView extends RecyclerView {

    private WrapperRecyclerAdapter mWrapperRecyclerAdapter;

    public WrapperRecyclerView(Context context) {
        super(context);
    }

    public WrapperRecyclerView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public WrapperRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public void setAdapter(Adapter adapter) {
        mWrapperRecyclerAdapter = new WrapperRecyclerAdapter(adapter);
        super.setAdapter(mWrapperRecyclerAdapter);
    }

    public void addHeaderView(View view) {
        if (mWrapperRecyclerAdapter != null) {
            mWrapperRecyclerAdapter.addHeaderView(view);
        }
    }

    public void removeHeaderView(View view) {
        if (mWrapperRecyclerAdapter != null) {
            mWrapperRecyclerAdapter.removeHeaderView(view);
        }
    }

    public void addFooterView(View view) {
        if (mWrapperRecyclerAdapter != null) {
            mWrapperRecyclerAdapter.addFooterView(view);
        }
    }

    public void removeFooterView(View view) {
        if (mWrapperRecyclerAdapter != null) {
            mWrapperRecyclerAdapter.removeFooterView(view);
        }
    }
}

MainActivity2類代碼：

public class MainActivity2 extends AppCompatActivity {

    private WrapperRecyclerView recyclerView;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_recyclerview2);

        ArrayList<String> datas = new ArrayList<>();
        for (int i = 0; i < 15; i++) {
            datas.add(" WrapperRecyclerView data " + i);
        }


        recyclerView = findViewById(R.id.recyclerview);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        //設(shè)置布局管理器
        recyclerView.setLayoutManager(layoutManager);
        //設(shè)置為垂直布局，這也是默認(rèn)的
        layoutManager.setOrientation(OrientationHelper.VERTICAL);
        //設(shè)置Adapter
        Adapter recycleAdapter = new Adapter(datas);
        //WrapperRecyclerAdapter adapter = new WrapperRecyclerAdapter(recycleAdapter);
        recyclerView.setAdapter(recycleAdapter);

        //View headerView = LayoutInflater.from(this).inflate(R.layout.header_view, null);//todo 這樣寫效果不對
        View headerView = LayoutInflater.from(this).inflate(R.layout.header_view, recyclerView, false);
        View footerView = LayoutInflater.from(this).inflate(R.layout.footer_view, recyclerView, false);

        recyclerView.addHeaderView(headerView);
        recyclerView.addFooterView(footerView);
        //設(shè)置分隔線
        //recyclerView.addItemDecoration(new DividerGridItemDecoration(this));
        //設(shè)置增加或刪除條目的動畫
        recyclerView.setItemAnimator(new DefaultItemAnimator());

    }


}

布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.ivyzh.designpatterndemo.d1_singleton_pattern.MainActivity">

    <com.ivyzh.designpatterndemo.d4_decorator_pattern.simple2.WrapperRecyclerView
        android:id="@+id/recyclerview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

</LinearLayout>

說明：上面的例子有個bug创南，就是點(diǎn)擊item刪除的時候伦忠，會有復(fù)用bug，如下圖：

刪除條目的Bug.png

后面會再排查扰藕。

END.