MultiTypeListViewAdapter，顾名思义。其封装了多type下的Adapter的编程模式，通过对每种type统一接口，利用多态的方式，将type的实现从Adapter中抽离出来。Adapter只需面向统一接口，所以可以提供一个通用实现，实现代码不再变动。而会变动的每个type对应的item实现，则由使用者自己去实现。对扩展开放，对修改封闭。
同时，由于每个type的item均被抽离出来了。相当于复用的粒度为每个type item，可以根据需要，动态地选择合适的item去添加到adapter中。提高了代码复用，每个人编写维护好自己的item即可，避免了多人合作时都去修改Adapter，容易造成冲突。
另外，由于ViewHolder 模式的规范，MultiTypeListViewAdapter也同时封装了ViewHolder模式。
常见的ListView Adapter 实现
先看一下常见的ListAdapter 实现，分为单个type和多type两种情况。
1、单Type的Adapter
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| class ListAdapter extend BaseAdapter {
...
private List<String> contents = new ArrayList();
...
public View getView(int position, View convertView, ViewGroup parent) {
String item = getItem(position);
if(null == item) {
throw new RuntimeException("list item is never null. pos:" + position);
} else {
ViewHolder holder;
if(null == convertView) {
holder = createViewHolder(parent);
convertView = holder.itemView;
convertView.setTag(holder);
} else {
holder = (ViewHolder)convertView.getTag();
}
item.updateHolder(holder, position);
return convertView;
}
}
}
private ViewHolder createViewHolder(ViewGroup parent) {
...
}
private void updateHolder(ViewHolder holder, String item) {
holder.text.setText(item);
}
private class ViewHolder {
TextView text;
ViewHolder(View itemView) {
text = (TextView)itemView.findViewById(R.id.text);
}
}
...
}
|
应该是挺常见的写法吧，继续往下。
2、多type的adapter
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| class ListAdapter extend BaseAdapter {
...
private List<String> contents = new ArrayList();
...
public int getItemViewType(int position) {
if (position % 2 == 0) {
return 0;
}
return 1;
}
public int getViewTypeCount() {
return 2;
}
public View getView(int position, View convertView, ViewGroup parent) {
String item = getItem(position);
if(null == item) {
throw new RuntimeException("list item is never null. pos:" + position);
} else {
ViewHolder holder;
if(null == convertView) {
if (getItemViewType(position) == 0) {
holder = createViewHolder(parent);
} else if (getItemViewType(position) == 1) {
holder = createViewHolder1(parent);
}
convertView = holder.itemView;
convertView.setTag(holder);
} else {
holder = (ViewHolder)convertView.getTag();
}
if (getItemViewType(position) == 0) {
item.updateHolder(holder, position);
} else if (getItemViewType(position) == 1) {
item.updateHolder1(holder, position);
}
return convertView;
}
}
}
private ViewHolder createViewHolder(ViewGroup parent) {
...
}
private void createViewHolder1(ViewGroup parent) {
...
}
private void updateHolder(ViewHolder holder, String item) {
holder.text.setText(item);
}
private void updateHolder1(ViewHolder1 holder, String item) {
holder.text.setText(item);
holder.img.setImageResoure(R.drawable.img);
}
private class ViewHolder {
TextView text;
ViewHolder(View itemView) {
text = (TextView)itemView.findViewById(R.id.text);
}
}
private class ViewHolder1 {
TextView text;
ImageView img;
ViewHolder(View itemView) {
text = (TextView)itemView.findViewById(R.id.text);
img = (ImageView)itemView.findViewById(R.id.img);
}
}
...
}
|
看到这里，是否感觉这个Adapter的getView（）开始有些让人不舒服了呢。若type再进一步增加，难不成还得继续if/else下去，adapter变得又臭又长。估计往后下去，就再没人愿意维护了。而且，这个Adapter的这一堆代码还得到处重复写下去，每个有listView的地方，都得配套一个adapter。针对这个坑，我设计了MultiTypeListViewAdapter来解决。希望能帮助到有需要的程序猿们~
使用 MultiTypeListViewAdapter
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| public class MainActivity extends AppCompatActivity {
private ListView listView;
private MultiTypeArrayAdapter adapter;
private static final int ITEM_TYPE_1 = 0;
private static final int ITEM_TYPE_2 = 1;
private static final int ITEM_TYPE_COUNT = 2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView) findViewById(R.id.listview);
adapter = new MultiTypeArrayAdapter(ITEM_TYPE_COUNT);
listView.setAdapter(adapter);
setupAdapter();
}
private void setupAdapter() {
adapter.setTypeCount(ITEM_TYPE_COUNT);
LineListItem1 item1 = new LineListItem1(this, ITEM_TYPE_1, "line type 1");
LineListItem2 item2 = new LineListItem2(this, ITEM_TYPE_2, "line type 2");
adapter.setNotifyOnChange(false);
for (int i = 0, len = 50; i < len; i++) {
adapter.addItem( i % 2 == 0 ? item1 : item2);
}
adapter.notifyDataSetChanged();
}
}
public class LineListItem1 extends BaseListItem {
private String line;
public LineListItem1(Context mContext, int viewType, String line) {
super(mContext, viewType);
this.line = line;
}
@Override
protected int onGetItemLayoutRes() {
return R.layout.list_item1;
}
@Override
protected ViewHolder onCreateViewHolder(View itemView) {
return new LineViewHolder(itemView);
}
@Override
public void updateHolder(ViewHolder holder, int pos) {
LineViewHolder h = (LineViewHolder) holder;
h.text.setText(line + "_" + pos);
}
private class LineViewHolder extends ViewHolder {
TextView text;
public LineViewHolder(View itemView) {
super(itemView);
text = (TextView) itemView.findViewById(R.id.line_text);
}
}
}
public class LineListItem2 extends BaseListItem {
private String line;
public LineListItem2(Context mContext, int viewType, String line) {
super(mContext, viewType);
this.line = line;
}
@Override
protected int onGetItemLayoutRes() {
return R.layout.list_item2;
}
@Override
protected ViewHolder onCreateViewHolder(View itemView) {
return new LineViewHolder2(itemView);
}
@Override
public void updateHolder(ViewHolder holder, int pos) {
LineViewHolder2 h = (LineViewHolder2) holder;
h.text.setText(line + "_" + pos);
h.img.setImageResource(R.drawable.icon_git);
}
private class LineViewHolder2 extends ViewHolder {
ImageView img;
TextView text;
public LineViewHolder2(View itemView) {
super(itemView);
img = (ImageView) itemView.findViewById(R.id.thumb);
text = (TextView) itemView.findViewById(R.id.name);
}
}
}
|
可以看到，使用MultiTypeListViewAdapter之后，实现多type的Adapter变得相当简单了。再也不用面对一堆判断itemType的if/else了。每增加一种type，只需增加一种新的ListItem即可，再也不用去改动Adapter的代码了。
项目发布在github上了，MultiTypeListViewAdapter，欢迎fork和交流。
