针对评论里问题的补充（补）DataBind 不写adapter和viewholder了
1、 项目gradle 引入databind支持
android{
...
dataBinding {
enabled = true
}
...
}
复制代码2、databind 基本功能介绍
（抄的介绍。。。真多）
- 单纯的摆脱findviewbyid
- 绑定基本数据类型及String
- 绑定Model数据
- 绑定事件
- 通过静态方法转换数据类型
- 通过运算符操作数据
- 自定义Binding的类名
- 绑定相同Model的操作
- model变量改变自动更新数据
- 绑定List/Map等集合数据
- Observable自动更新
- Databinding与include标签的结合
- DataBinding与RecyclerView的结合
3、简单使用
a.创建一个类（这里用简单的实体类）
public class User {
private String text;
public User(String text) {
this.text = text;
}
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
}
复制代码b.创建一个布局 显示User的text属性
activity_main.xml
"1.0" encoding="utf-8"?>
"http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
"@+id/main_btn3"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@{user.text}" />
复制代码c、在布局中使用
public class MainActivity extends AppCompatActivity {
//注意
//注意
//注意
//注意
//引入前 要makeProject 生成代码
private ActivityMainBinding binding;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//通过DataBInding加载布局都会对应的生成一个对象，如ActivityMainBinding，对象名在布局文件名称后加上了一个后缀Binding
binding = DataBindingUtil.setContentView(MainActivity.this, R.layout.activity_main);
//绑定model对象数据
User user = new User("绑定Model数据类型");
binding.setUser(user);
//或者 binding.setVariable(BR.user,user);
}
//运行就会发现TextView的text已经改变
}
复制代码4、开始啦
a、算术入门啦 进入正题
//老规矩 先写布局 布局很简单 就一个textView 一个recycler
"1.0" encoding="utf-8"?>
"http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="lzf.one.adapter.MainActivity">
"@+id/text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="9dp"
android:text="点击显示recycler"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
"@+id/recycler"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:visibility="gone"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@id/text" />
复制代码c、创建model 给上面布局使用
//实体类 给recycler的item用 为了方便 写的简单
public class UserInfo {
private String name;
private String age;
public UserInfo(String name, String age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAge() {
return age;
}
public void setAge(String age) {
this.age = age;
}
}
//model 提供数据 提供一个userInfoList 没啥毛病
public class UserViewModel {
private List userInfoList;
public UserViewModel() {
this.userInfoList = new ArrayList<>();
}
public List getUserInfoList(){
userInfoList.add(new UserInfo("张三","25岁"));
userInfoList.add(new UserInfo("张三","25岁"));
userInfoList.add(new UserInfo("张三","25岁"));
userInfoList.add(new UserInfo("张三","25岁"));
return userInfoList;
}
}
复制代码 d、数据准备好了 我们开始写啦
public class MainActivity extends AppCompatActivity {
private ActivityMainBinding mBind;
private UserViewModel userViewModel;
private MyAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mBind = DataBindingUtil.setContentView(this, R.layout.activity_main);
mBind.text.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mBind.recycler.setVisibility(View.VISIBLE);
}
});
mBind.recycler.setLayoutManager(new LinearLayoutManager(this));
userViewModel=new UserViewModel();
adapter=new MyAdapter(this,userViewModel.getUserInfoList());
mBind.recycler.setAdapter(adapter);
}
}
//接下来 我们开始写adapter 我们先正常写
public class MyAdapter extends RecyclerView.Adapter{
private Context context;
private List userInfoList;
MyAdapter(Context context, List userInfoList) {
this.context = context;
this.userInfoList = userInfoList;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
UserItemBinding userItemBinding= DataBindingUtil.inflate(LayoutInflater.from(context),R.layout.user_item,parent,false);
return new MyViewHolder(userItemBinding);
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
UserItemBinding userItemBinding=holder.getUserItemBinding();
userItemBinding.setUser(userInfoList.get(position));
userItemBinding.executePendingBindings();
}
@Override
public int getItemCount() {
return userInfoList==null?0:userInfoList.size();
}
class MyViewHolder extends RecyclerView.ViewHolder{
UserItemBinding userItemBinding;
MyViewHolder(UserItemBinding userItemBinding) {
super(userItemBinding.getRoot());
this.userItemBinding=userItemBinding;
}
UserItemBinding getUserItemBinding() {
return userItemBinding;
}
}
}
复制代码 e、开始优化
我们先来优化ViewHolder
class MyViewHolder extends RecyclerView.ViewHolder{
UserItemBinding userItemBinding;
MyViewHolder(UserItemBinding userItemBinding) {
super(userItemBinding.getRoot());
this.userItemBinding=userItemBinding;
}
UserItemBinding getUserItemBinding() {
return userItemBinding;
}
}
UserItemBinding 继承 ViewDataBinding
根据多态 那么 我们可以把viewholder里的UserItemBinding改成ViewDataBinding
class MyViewHolder extends RecyclerView.ViewHolder{
ViewDataBinding viewDataBinding;
MyViewHolder(ViewDataBinding viewDataBinding) {
super(viewDataBinding.getRoot());
this.viewDataBinding=viewDataBinding;
}
ViewDataBinding getViewDataBinding() {
return viewDataBinding;
}
}
这样来看 viewholder就不再依赖一个具体的databinding而是依赖ViewDataBinding(父类)
那么viewHolder现在是通用的了 我可以一直使用
复制代码我们再来优化adapter 要adapter实现万能最起码的 要实现多类型item 关于 Android Adapter，你的实现方式可能一直都有问题 我们可以类似的实现 将Item的layoutId当作Itme的viewType。我们先来改造实体类UserInfo
//写个接口 定义一个规范
public interface BindAdapterType {
int getType();
}
//userInfo实现接口
public class UserInfo implements BindAdapterType {
private String name;
private String age;
public UserInfo(String name, String age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAge() {
return age;
}
public void setAge(String age) {
this.age = age;
}
//注意
@Override
public int getType() {
//返回layoutId 当作userItem的viewType
return R.layout.user_item;
}
}
复制代码那么 现在我们的adapter变成什么样了呢
public class MyAdapter extends RecyclerView.Adapter{
private Context context;
private List userInfoList;
MyAdapter(Context context, List userInfoList) {
this.context = context;
this.userInfoList = userInfoList;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
return new MyViewHolder(DataBindingUtil.
inflate(LayoutInflater.from(context),
viewType,parent,false));
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
//这里编译过不去 别急 一点点改
UserItemBinding userItemBinding=holder.getViewDataBinding();
userItemBinding.setUser(userInfoList.get(position));
userItemBinding.executePendingBindings();
}
@Override
public int getItemCount() {
return userInfoList==null?0:userInfoList.size();
}
@Override
public int getItemViewType(int position) {
return userInfoList.get(position).getType();
}
}
复制代码 这时候 我们会看到onCreateViewHolder（）不再依赖具体的layoutId啦，而是userInfo固有的属性Type,viewholder也是通用的了，那么我们的onCreateViewHolder（）算是改造完成了 接着我们来改造onBindViewHolder（）
//这里有个前置的知识
//对于每个"http://schemas.android.com/apk/res-auto">
"user"
type="lzf.one.adapter.UserInfo" />
"http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content">
//节省空间 里面的内容删掉了 就是user_item.xml
那么onBindViewHolder（）我们就可以改造成这样
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.getViewDataBinding().setVariable(BR.user,userInfoList.get(position));
holder.getViewDataBinding().executePendingBindings();
}
//在这里BR.user这个id是user_item.xml的user的资源id
//user_item又引用了userInfo,我们是不是可以类似viewType的方式 把id当作userInfo的属性呢？
//我们来试试
复制代码改造接口
public interface BindAdapterType {
int getType();
int getId();
}
复制代码userInfo 实现getId()方法
//get/set方法去掉 展示主要内容
public class UserInfo implements BindAdapterType {
private String name;
private String age;
public UserInfo(String name, String age) {
this.name = name;
this.age = age;
}
@Override
public int getType() {
return R.layout.user_item;
}
@Override
public int getId() {
return BR.user;
}
}
复制代码那么现在onBindViewHolder（）就变成什么样了呢？我们来看一下：
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.getViewDataBinding().setVariable(
userInfoList.get(position).getId(),
userInfoList.get(position));
holder.getViewDataBinding().executePendingBindings();
}
复制代码到现在我们已经基本改造完成了 现在我们可以把List的泛型换掉了 他已经不再单纯的是userInfo 而是list data(userInfo 实现了接口BindAdapterType)； 现在 我们已经改造成功了 我们来看看完整的代码
//现在adapter不再限定接受userInfo的集合了 而是任何实现了BingAdapterType接口的实体
//可以是userInfo 也可以是studentInfo
//只要实现了BindAdapterType接口就行（getType()、getId()的返回值还是要给的（0.0）
//至于item的交互 你就在对应的实体里面写呗
public class MyAdapter extends RecyclerView.Adapter{
private Context context;
private List userInfoList;
MyAdapter(Context context, List userInfoList) {
this.context = context;
this.userInfoList = userInfoList;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
return new MyViewHolder(DataBindingUtil.
inflate(LayoutInflater.from(context),
viewType,parent,false));
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.getViewDataBinding().setVariable(userInfoList.get(position).getId(),userInfoList.get(position));
holder.getViewDataBinding().executePendingBindings();
}
@Override
public int getItemCount() {
return userInfoList==null?0:userInfoList.size();
}
@Override
public int getItemViewType(int position) {
return userInfoList.get(position).getType();
}
class MyViewHolder extends RecyclerView.ViewHolder{
ViewDataBinding viewDataBinding;
MyViewHolder(ViewDataBinding viewDataBinding) {
super(viewDataBinding.getRoot());
this.viewDataBinding=viewDataBinding;
}
ViewDataBinding getViewDataBinding() {
return viewDataBinding;
}
}
}
复制代码 代码地址