Jetpack(一)Lifecycle和LiveData
Jetpack(二)之DataBinding
Jetpack(三) 之 Room 与 ViewModel
我们设计一个User，不断更新name，来作为入口进行DataBinding分析
关于使用，这里不介绍过多。官网查询即可。
注意gradle 配置 dataBiding true 即可
测试代码
上述就是我页面的layout
model User
public class User extends BaseObservable {
public String name;
-> 这个标签才能让我们进行绑定
@Bindable
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
-> 系统会帮我们生成BR文件
notifyPropertyChanged(BR.name);
}
public User(String name) {
this.name = name;
}
}
Activity页面
public class SecondActivity extends AppCompatActivity {
ActivitySecondBinding activitySecondBinding;
User user;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// setContentView(R.layout.activity_second);
user = new User("David");
activitySecondBinding = DataBindingUtil.setContentView(this,
R.layout.activity_second);
activitySecondBinding.tv.setText(user.getName());
final Handler handler = new Handler();
handler.post(new Runnable() {
@Override
public void run() {
user.setName(user.name + "1");
// activitySecondBinding.setUser(user);
activitySecondBinding.setVariable(BR.user, user);
Log.d("zcw:::", Thread.currentThread().getName());
handler.postDelayed(this, 1000);
}
});
}
}
原理分析
------------------> layout 和 页面 自动生成两个xml 文件
我们的layout 和正常布局 在编译后：xml会自动进行分离
app/build/intermediates/data_binding_layout_info_type_merge/debug/out/activity_second-layout.xml
使我们的layout单独抽离的xml
app/build/intermediates/incremental/mergeDebugResources/stripped.dir/layout/activity_second.xml
这个是去掉layout标签内容的我们熟悉的布局文件
false
-----------------> 代码入口
我们发现
-> 这两句话作用是一样的
activitySecondBinding.setUser(user)
activitySecondBinding.setVariable(BR.user, user);
系统帮我们生成的BR文件
public class BR {
public static final int _all = 0;
public static final int name = 1;
public static final int user = 2;
public static final int vm = 3;
}
一下三种情况会对应生成BR
1.xml中设置variable的name属性
2.VM继承BaseObservable，将某个成员变量加上@Bindable注解
3.VM继承BaseObservable，将get,set,is开头的方法加上@Bindable注解
进入setVariable 看源码结构,发现只有一个抽象方法的接口。实际上这种情况是APT 生成的代码实现。
build/generated/ap_generated_sources/debug/out/top/zcwfeng/jetpack/databinding/ActivitySecondBindingImpl.java
-> 最终还是调用了setUser
@Override
public boolean setVariable(int variableId, @Nullable Object variable) {
boolean variableSet = true;
if (BR.user == variableId) {
setUser((top.zcwfeng.jetpack.bean.User) variable);
}
else {
variableSet = false;
}
return variableSet;
}
public void setUser(@Nullable top.zcwfeng.jetpack.bean.User User) {
updateRegistration(0, User);
this.mUser = User;
synchronized(this) {
mDirtyFlags |= 0x1L;
}
notifyPropertyChanged(BR.user);
super.requestRebind();
}
updateRegisteration 方法
进入源码会发先，传入WeakListener 没有就创建一个监听器，这个监听器持有一个WeakPropertyListener 数组
进入了ViewDataBinding的updateRegisteration 方法做了两件事
如果传入的监听为null反注册-> unregisterFrom。然后创建对应BR中属性的监听
在进行->registerTo 方法操作。
不空的话。也是先 -> unregisterFrom 在注册->registerTo
private boolean updateRegistration(int localFieldId, Object observable,
CreateWeakListener listenerCreator) {
if (observable == null) {
return unregisterFrom(localFieldId);
}
WeakListener listener = mLocalFieldObservers[localFieldId];
if (listener == null) {
registerTo(localFieldId, observable, listenerCreator);
return true;
}
if (listener.getTarget() == observable) {
return false;//nothing to do, same object
}
unregisterFrom(localFieldId);
registerTo(localFieldId, observable, listenerCreator);
return true;
}
----------------------> 另外的View 代码入口
DataBindingUtils.setContentView
DataBinderMapperImpl （返回ViewDataBinding控制）
关注一下代码里面-> 「说明」
@Override
public ViewDataBinding getDataBinder(DataBindingComponent component, View view, int layoutId) {
int localizedLayoutId = INTERNAL_LAYOUT_ID_LOOKUP.get(layoutId);
if(localizedLayoutId > 0) {
final Object tag = view.getTag();
if(tag == null) {
throw new RuntimeException("view must have a tag");
}
switch(localizedLayoutId) {
case LAYOUT_ACTIVITYMAIN: {
if ("layout/activity_main_0".equals(tag)) {
return new ActivityMainBindingImpl(component, view);
}
throw new IllegalArgumentException("The tag for activity_main is invalid. Received: " + tag);
}
case LAYOUT_ACTIVITYSECOND: {
->这里是不是很熟悉，就是activity_second 拼接了BR文件的tag解析layout的布局文件
if ("layout/activity_second_0".equals(tag)) {
return new ActivitySecondBindingImpl(component, view);
}
throw new IllegalArgumentException("The tag for activity_second is invalid. Received: " + tag);
}
}
}
return null;
}
代码 new ActivitySecondBindingImpl->invalidateALL
-> ViewDataBinding:requestRebind 刷新界面
但是UI是怎么填充
我们发现ViewDataBinding 有个静态块初始化了监听
ViewDataBinding-------->static 块
static {
if (VERSION.SDK_INT < VERSION_CODES.KITKAT) {
ROOT_REATTACHED_LISTENER = null;
} else {
ROOT_REATTACHED_LISTENER = new OnAttachStateChangeListener() {
@TargetApi(VERSION_CODES.KITKAT)
@Override
public void onViewAttachedToWindow(View v) {
// execute the pending bindings.
final ViewDataBinding binding = getBinding(v);
binding.mRebindRunnable.run();
v.removeOnAttachStateChangeListener(this);
}
@Override
public void onViewDetachedFromWindow(View v) {
}
};
}
}
执行了任务 mRebindRunnable
-> executePendingBindings()
-> executeBindings() 发现是abstract 方法
还是代码生成ActivitySecondImpl类里面
@Override
protected void executeBindings() {
long dirtyFlags = 0;
synchronized(this) {
dirtyFlags = mDirtyFlags;
mDirtyFlags = 0;
}
java.lang.String userName = null;
top.zcwfeng.jetpack.bean.User user = mUser;
if ((dirtyFlags & 0x7L) != 0) {
if (user != null) {
// read user.name
userName = user.getName();
}
}
// batch finished
if ((dirtyFlags & 0x7L) != 0) {
// api target 1
androidx.databinding.adapters.TextViewBindingAdapter.setText(this.tv, userName);
}
}
// Listener Stub Implementations
// callback impls
// dirty flag
private long mDirtyFlags = 0xffffffffffffffffL;
/* flag mapping
flag 0 (0x1L): user
flag 1 (0x2L): user.name
flag 2 (0x3L): null
flag mapping end*/
//end
}
发现了一个细节。之前我们初始化是 |= 将对应的 2的n次方位置变成1 证明我们更新。这次在& 操作判断是否为0，是0 证明之前更新1有问题。不是我们就更新界面
这块需要---------> 第三个入口 notifyPropertyChanged(BR.name);
这个在这个类里面实现，上面我们看到了这个类在监听回调中
PropertyChangeRegistry-> onPropertyChanged
WeakPropertyListener 中实现onPropertyChanged
@Override
public void onPropertyChanged(Observable sender, int propertyId) {
ViewDataBinding binder = mListener.getBinder();
if (binder == null) {
return;
}
Observable obj = mListener.getTarget();
if (obj != sender) {
return; // notification from the wrong object?
}
binder.handleFieldChange(mListener.mLocalFieldId, sender, propertyId);
}
handleFieldChange -》onFieldChange 一个抽象方法。
ActivitySecondBindingImpl - >onFieldChange 实现->onChangeUser-》
private boolean onChangeUser(top.zcwfeng.jetpack.bean.User User, int fieldId) {
if (fieldId == BR._all) {
synchronized(this) {
mDirtyFlags |= 0x1L;
}
return true;
}
else if (fieldId == BR.name) {
synchronized(this) {
mDirtyFlags |= 0x2L;
}
return true;
}
return false;
}
整体的简图就是这样
总结：入口就是这个两个
setVariable(xxxx)
notifyPropertyChanged(BR.name);