最近在看一本名为《Android源码设计模式解析与实战》的书，表示看完如果不及时敲一偏还真容易忘记，刚好看到装饰者模式，这里就敲一个有关这个思想的代码。
装饰模式定义：动态的给一个对象添加额外的职责，使得这个对象的功能越来越丰富。
我们先把最原始的使用RecyclerView的步骤写一篇然后再升级为最终版。
布局很简单，就不在多说，个人习惯喜欢从Adapter入手，我们创建一个类，实现最简单的Adapter，下面是BaseRaleAdapter：
public class BaseRaleAdapter extends RecyclerView.Adapter{
private List mList;
private Context mContext;
public BaseRaleAdapter(Context context,List list){
this.mList=list;
mContext=context;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
return new ViewHolder(LayoutInflater.from(mContext).inflate(R.layout.expand_item_layout,parent,false));
}
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
holder.mTest.setText(mList.get(position));
}
@Override
public int getItemCount() {
return mList.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
private final TextView mTest;
public ViewHolder(View itemView) {
super(itemView);
mTest = itemView.findViewById(R.id.test);
}
}
}
然后再Activity里面使用
public class Main20Activity extends AppCompatActivity {
private RecyclerView mRecyclerView;
private BaseRaleAdapter mBaseRaleAdapter;
private List mList=new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main20);
mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
LinearLayoutManager linearLayout=new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(linearLayout);
mBaseRaleAdapter = new BaseRaleAdapter(Main20Activity.this,mList);
mRecyclerView.setAdapter(mBaseRaleAdapter);
}
@Override
protected void onResume() {
super.onResume();
for(int x=0;x<20;x++){
mList.add(x+"");
}
mBaseRaleAdapter.notifyDataSetChanged();
}
}
这就是最基础的使用了，那么我们将BaseRaleAdapter进行扩展，就运用到装饰者模式了，原本你没有添加头部和底部的功能，哎~？我将你包裹一下，就能拓展出这两个功能了，来，继续走下去。
创建一个ExpandAdapter，顾名思义他就是拓展adapter，他也是和BaseRaleAdapter一样，也是集成于RecyclerView.Adapter<>，但是尖括号里面的内容就不是BaseRaleAdapter.ViewHolder了，而是RecyclerView.ViewHolder，因为等下在onCreateViewHolder中我们不仅要返回正常item的ViewHolder也要返回头部与底部的ViewHolder，所以这样做可以兼容。
public class ExpandAdapter extends RecyclerView.Adapter{
private RecyclerView.Adapter mRealAdpter;
private List mHanders=new ArrayList<>();
private List mFoots=new ArrayList<>();
public ExpandAdapter(RecyclerView.Adapter realAdpter){
this.mRealAdpter=realAdpter;
}
/**
* 由于下面需要获取ViewHolder，那肯定是需要当前位置，但是onCreateViewHolder唯一与position有关的就是viewType
* 所以我们需要复写getItemViewType,让其返回position而不是type
* @param parent
* @param position
* @return
*/
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int position) {
//如果是头部就返回头部的ViewHolder
int handersNumber = mHanders.size();
if(position 然后更新下Activity的使用代码，将原来的BaseRaleAdapter包裹在里面，
public class Main20Activity extends AppCompatActivity {
private RecyclerView mRecyclerView;
private BaseRaleAdapter mBaseRaleAdapter;
private List mList=new ArrayList<>();
private ExpandAdapter mExpandAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main20);
mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
LinearLayoutManager linearLayout=new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(linearLayout);
mBaseRaleAdapter = new BaseRaleAdapter(Main20Activity.this,mList);
mExpandAdapter = new ExpandAdapter(mBaseRaleAdapter);
mRecyclerView.setAdapter(mExpandAdapter);
View view = LayoutInflater.from(Main20Activity.this).inflate(R.layout.layout_hander, mRecyclerView, false);
mExpandAdapter.addHanderView(view);
}
@Override
protected void onResume() {
super.onResume();
for(int x=0;x<20;x++){
mList.add(x+"");
}
mBaseRaleAdapter.notifyDataSetChanged();
}
}
头部的布局
微信图片_20180719174812.jpg
这样简单的封装就出来了，我们就完成了装饰。，，
你会发现一个问题，在activity中，使用这个封装好的Adapter有点步骤太多，别人使用的时候要注意的也多，那怎么简化呢？我们可以参考ListView，so？我们能不能将Adapter的偷梁换柱放到RecyclerView中呢？好！说干就干，创建一个ExpandRecyclerView
public class ExpandRecyclerView extends RecyclerView{
private ExpandAdapter mExpandAdapter;
public ExpandRecyclerView(Context context) {
super(context);
}
public ExpandRecyclerView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}
public ExpandRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
/**
* 偷梁换柱
* @param adapter
*/
@Override
public void setAdapter(Adapter adapter) {
mExpandAdapter=new ExpandAdapter(adapter);
super.setAdapter(mExpandAdapter);
}
/**
* 添加头部
* @param view
*/
public void addHanderView(View view){
if(mExpandAdapter!=null){
mExpandAdapter.addHanderView(view);
}
}
/**
* 添加底部
* @param view
*/
public void addFootView(View view){
if(mExpandAdapter!=null){
mExpandAdapter.addFootView(view);
}
}
/**
* 移除头部
* @param view
*/
public void removeHanderView(View view){
if(mExpandAdapter!=null){
mExpandAdapter.removeHanderView(view);
}
}
/**
* 移除底部
* @param view
*/
public void removeFootView(View view){
if(mExpandAdapter!=null){
mExpandAdapter.removeFootView(view);
}
}
}
这样在Activity的使用中，就会变得简单
public class Main20Activity extends AppCompatActivity {
private ExpandRecyclerView mRecyclerView;
private BaseRaleAdapter mBaseRaleAdapter;
private List mList=new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main20);
mRecyclerView = (ExpandRecyclerView) findViewById(R.id.recycler_view);
LinearLayoutManager linearLayout=new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(linearLayout);
mBaseRaleAdapter = new BaseRaleAdapter(Main20Activity.this,mList);
mRecyclerView.setAdapter(mBaseRaleAdapter);
View view = LayoutInflater.from(Main20Activity.this).inflate(R.layout.layout_hander, mRecyclerView, false);
mRecyclerView.addHanderView(view);
}
@Override
protected void onResume() {
super.onResume();
for(int x=0;x<20;x++){
mList.add(x+"");
}
mBaseRaleAdapter.notifyDataSetChanged();
}
}
当然，Activity的布局中就要应用我们自定义的ExpandRecyclerView 而不是RecyclerView了。
以前我就是用上面这些代码使用的，但是有一次被同事指出一个bug，就是删除一行条目时，没有及时刷新，这样，我们稍微修改下代码来验证下
public class BaseRaleAdapter extends RecyclerView.Adapter{
private List mList;
private Context mContext;
public BaseRaleAdapter(Context context,List list){
this.mList=list;
mContext=context;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
return new ViewHolder(LayoutInflater.from(mContext).inflate(R.layout.expand_item_layout,parent,false));
}
@Override
public void onBindViewHolder(ViewHolder holder, final int position) {
holder.mTest.setText(mList.get(position));
//移除测试
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
mList.remove(position);
notifyDataSetChanged();
}
});
}
@Override
public int getItemCount() {
return mList.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
private final TextView mTest;
public ViewHolder(View itemView) {
super(itemView);
mTest = itemView.findViewById(R.id.test);
}
}
}
BaseRaleAdapter中加上了点击删除功能，发现根本没用，因为BaseRaleAdapter调用了notifyDataSetChanged但是我们ExpandAdapter并没有相应，所以界面也是没有变化的，所以在ExpandAdapter中要监听BaseRaleAdapter调用了notifyDataSetChanged，然后也使用ExpandAdapter调用一次notifyDataSetChanged就行，好！我们就修改一下ExpandAdapter
public class ExpandAdapter extends RecyclerView.Adapter{
private RecyclerView.Adapter mRealAdpter;
private List mHanders=new ArrayList<>();
private List mFoots=new ArrayList<>();
public ExpandAdapter(RecyclerView.Adapter realAdpter){
this.mRealAdpter=realAdpter;
//监听BaseRaleAdapter调用了notifyDataSetChanged，然后也使用ExpandAdapter调用一次notifyDataSetChanged
realAdpter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
@Override
public void onChanged() {
super.onChanged();
notifyDataSetChanged();
}
});
}
/**
* 由于下面需要获取ViewHolder，那肯定是需要当前位置，但是onCreateViewHolder唯一与position有关的就是viewType
* 所以我们需要复写getItemViewType,让其返回position而不是type
* @param parent
* @param position
* @return
*/
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int position) {
//如果是头部就返回头部的ViewHolder
int handersNumber = mHanders.size();
if(position