Jetpack(一)Lifecycle和LiveData
Jetpack(二)之DataBinding
Jetpack(三) 之 Room 與 ViewModel
我們?cè)O(shè)計(jì)一個(gè)User贡未，不斷更新name杜恰，來(lái)作為入口進(jìn)行DataBinding分析
關(guān)于使用，這里不介紹過(guò)多蒙揣。官網(wǎng)查詢即可魏铅。
注意gradle 配置 dataBiding true 即可
測(cè)試代碼
<?xml version="1.0" encoding="utf-8"?>
<layout>
<data>
<variable
name="user"
type="top.zcwfeng.jetpack.bean.User" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="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=".SecondActivity">
<TextView
android:id="@+id/tv"
android:text="@{user.name}"
android:layout_width="match_parent"
android:layout_height="60dp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
上述就是我頁(yè)面的layout
model User
public class User extends BaseObservable {
public String name;
-> 這個(gè)標(biāo)簽才能讓我們進(jìn)行綁定
@Bindable
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
-> 系統(tǒng)會(huì)幫我們生成BR文件
notifyPropertyChanged(BR.name);
}
public User(String name) {
this.name = name;
}
}
Activity頁(yè)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 頁(yè)面 自動(dòng)生成兩個(gè)xml 文件
我們的layout 和正常布局 在編譯后：xml會(huì)自動(dòng)進(jìn)行分離
app/build/intermediates/data_binding_layout_info_type_merge/debug/out/activity_second-layout.xml
使我們的layout單獨(dú)抽離的xml
app/build/intermediates/incremental/mergeDebugResources/stripped.dir/layout/activity_second.xml
這個(gè)是去掉layout標(biāo)簽內(nèi)容的我們熟悉的布局文件
<?xml version="1.0" encoding="utf-8"?>
<Layout layout="activity_second" modulePackage="top.zcwfeng.jetpack" filePath="app/src/main/res/layout/activity_second.xml" directory="layout" isMerge="false" isBindingData="true" rootNodeType="androidx.constraintlayout.widget.ConstraintLayout">
<Variables declared="true" type="top.zcwfeng.jetpack.bean.User" name="user">
<location startLine="3" startOffset="8" endLine="5" endOffset="50"/>
</Variables>
<Targets>
<Target tag="layout/activity_second_0" view="androidx.constraintlayout.widget.ConstraintLayout">
<Expressions/>
<location startLine="8" startOffset="4" endLine="24" endOffset="55"/>
</Target>
<Target id="@+id/tv" tag="binding_1" view="TextView">
<Expressions>
<Expression text="user.name" attribute="android:text">
<Location startLine="17" startOffset="12" endLine="17" endOffset="38"/>
<TwoWay>false</TwoWay>
<ValueLocation startLine="17" startOffset="28" endLine="17" endOffset="36"/>
</Expression>
</Expressions>
<location startLine="15" startOffset="8" endLine="22" endOffset="55"/>
</Target>
</Targets>
</Layout>
-----------------> 代碼入口
我們發(fā)現(xiàn)
-> 這兩句話作用是一樣的
activitySecondBinding.setUser(user)
activitySecondBinding.setVariable(BR.user, user);
系統(tǒng)幫我們生成的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;
}
一下三種情況會(huì)對(duì)應(yīng)生成BR
1.xml中設(shè)置variable的name屬性
2.VM繼承BaseObservable所袁，將某個(gè)成員變量加上@Bindable注解
3.VM繼承BaseObservable父泳，將get,set,is開(kāi)頭的方法加上@Bindable注解
進(jìn)入setVariable 看源碼結(jié)構(gòu),發(fā)現(xiàn)只有一個(gè)抽象方法的接口止潮。實(shí)際上這種情況是APT 生成的代碼實(shí)現(xiàn)窃判。
build/generated/ap_generated_sources/debug/out/top/zcwfeng/jetpack/databinding/ActivitySecondBindingImpl.java
-> 最終還是調(diào)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
進(jìn)入源碼會(huì)發(fā)先，傳入WeakListener 沒(méi)有就創(chuàng)建一個(gè)監(jiān)聽(tīng)器喇闸，這個(gè)監(jiān)聽(tīng)器持有一個(gè)WeakPropertyListener 數(shù)組
進(jìn)入了ViewDataBinding的updateRegisteration 方法做了兩件事
如果傳入的監(jiān)聽(tīng)為null反注冊(cè)-> unregisterFrom袄琳。然后創(chuàng)建對(duì)應(yīng)BR中屬性的監(jiān)聽(tīng)
在進(jìn)行->registerTo 方法操作。
不空的話燃乍。也是先 -> unregisterFrom 在注冊(cè)->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 代碼入口
DataBindingUtils.setContentView
DataBinderMapperImpl （返回ViewDataBinding控制）
關(guān)注一下代碼里面-> 「說(shuō)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: {
->這里是不是很熟悉唆樊，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;
}
代碼 new ActivitySecondBindingImpl->invalidateALL
-> ViewDataBinding:requestRebind 刷新界面
但是UI是怎么填充
我們發(fā)現(xiàn)ViewDataBinding 有個(gè)靜態(tài)塊初始化了監(jiān)聽(tīng)
ViewDataBinding-------->static 塊
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) {
}
};
}
}
執(zhí)行了任務(wù) mRebindRunnable
-> executePendingBindings()
-> executeBindings() 發(fā)現(xiàn)是abstract 方法
還是代碼生成ActivitySecondImpl類(lèi)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
}
發(fā)現(xiàn)了一個(gè)細(xì)節(jié)。之前我們初始化是 |= 將對(duì)應(yīng)的 2的n次方位置變成1 證明我們更新刻蟹。這次在& 操作判斷是否為0逗旁，是0 證明之前更新1有問(wèn)題。不是我們就更新界面
這塊需要---------> 第三個(gè)入口 notifyPropertyChanged(BR.name);
這個(gè)在這個(gè)類(lèi)里面實(shí)現(xiàn)舆瘪，上面我們看到了這個(gè)類(lèi)在監(jiān)聽(tīng)回調(diào)中
PropertyChangeRegistry-> onPropertyChanged
WeakPropertyListener 中實(shí)現(xiàn)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 一個(gè)抽象方法片效。
ActivitySecondBindingImpl - >onFieldChange 實(shí)現(xiàn)->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;
}
整體的簡(jiǎn)圖就是這樣
總結(jié)：入口就是這個(gè)兩個(gè)
setVariable(xxxx)
notifyPropertyChanged(BR.name);
