DataBinding原理
DataBinding原理
DataBinding 原理
编译阶段
以activity_test5.xml为例：
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<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
<data>
<variable
name="workBean"
type="com.zbt.databinding.ObservableWorkBean" />
<variable
name="eventBinding"
type="com.zbt.databinding.Test5Activity.EventBinding" />
</data>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="20dp"
android:orientation="vertical">
<TextView
style="@style/TvStyle"
android:text="model - View : 双向数据绑定" />
<TextView
style="@style/TvStyle"
android:text="@{workBean.name}" />
<EditText
style="@style/EtStyle"
android:layout_marginTop="10dp"
android:text="@={workBean.name}" />
<TextView
android:id="@+id/tv_title"
style="@style/TvStyle"
android:layout_marginTop="60dp"
android:text="事件绑定" />
<Button
android:id="@+id/tv_binding3"
style="@style/BtnStyle"
android:onClick="@{()->eventBinding.onNameClick(workBean)}"
android:text="@{workBean.name}" />
<EditText
style="@style/EtStyle"
android:layout_marginTop="10dp"
android:afterTextChanged="@{eventBinding::onAfterTextChanged}"
android:hint="@{workBean.name}" />
</LinearLayout>
</layout>
编译生成的代码：
编译 DataBinding 生成的代码主要有 activity_test5.xml、activity_test5-layout.xml、BR、DataBindingMapper、ActivityTest5Binding
activity_test5.xml
路径：build\intermediates\incremental\mergeDebugResources\stripped.dir\layout\activity_test5.xml
该文件是编写的 activity_test5.xml 去除 layout 标签的布局文件
actiivty_test5-layout.xml
路径：build\intermediates\data_binding_layout_info_type_merge\debug\out\actiivty_test5-layout.xml
该文件是根据标签 layout 生成的，对 activity_test5.xml 进行了扩展，其中主要标签如下：
- 包含 xml 地址、包名、根节点信息。
- model 信息
- model 指向的目标视图信息，其中 标签绑定了 tag 和 View
BR
生成在 build\generated\source\kapt\debug\com\xxx\databinding\BR.java；该目录主要根据 <variable> 和用 @Bindable 注解的字段生成 id，类似如资源生成的 id，ResId。
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public class BR {
public static final int _all = 0;
public static final int activity = 1;
public static final int employeeBean = 4;
public static final int eventBinding = 5;
// ...
public static final int workBean = 13;
public static final int workContent = 14;
public static final int workName = 15;
}
DataBindingmapperImpl
路径：build\generated\source\kapt\debug\com\xxx\databinding\DataBindingmapperImpl.java
该文件主要是存储 tag 绑定对应的 xml，以及 BR 中的 ID 与对应的字段
Activity5TestBinding
kotlin 编码的项目中会生成两个类：ActivityTest5Binding 和 ActivityTest5BindingImpl，其中前者是 abstract 类，后者是前者的子类。
路径：
build\generated\data_binding_base_class_source_out\debug\out\com\xxx\databinding\databinding\ActivityTest5Binding.javabuild\generated\source\kapt\debug\com\xxx\databinding\databinding\ActivityTest5BindingImpl.java
可以看到 ViewDataBinding 实现了 ViewBinding 接口，所以从这里也可看出 ViewBinding 是 DataBinding 子集。而 XxxBindingImpl 文件主要是生成相应的 View 及对 View 进行数据绑定。
绑定过程
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public void setUser(@Nullable me.hacket.assistant.samples.google.architecture.databinding.demos.demo1.CommonUser User) {
this.mUser = User;
synchronized(this) {
mDirtyFlags |= 0x40L;
}
notifyPropertyChanged(BR.user);
super.requestRebind();
}
以 setUser 为例
- 成员变量 mUser 赋值
- 同步代码块中加了 mDirtyFlags
- 调用 notifyPropertyChanged 通知 user 变化了
- 调用 requestRebind()
接着看 requestRebind()
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protected void requestRebind() {
if (mContainingBinding != null) {
// 1
mContainingBinding.requestRebind();
} else {
final LifecycleOwner owner = this.mLifecycleOwner;
if (owner != null) {
Lifecycle.State state = owner.getLifecycle().getCurrentState();
if (!state.isAtLeast(Lifecycle.State.STARTED)) {
// 2
return; // wait until lifecycle owner is started
}
}
synchronized (this) {
if (mPendingRebind) {
return;
}
mPendingRebind = true;
}
if (USE_CHOREOGRAPHER) {
// 3
mChoreographer.postFrameCallback(mFrameCallback);
} else {
// 4
mUIThreadHandler.post(mRebindRunnable);
}
}
}
mFrameCallback = new Choreographer.FrameCallback() {
@Override
public void doFrame(long frameTimeNanos) {
mRebindRunnable.run();
}
};
- 如果 mContainingBinding 不为空，先执行 requestRebind()；mContainingBinding 就是你当前这布局是被 mContainingBinding 给 include 了（或者说 mContainingBinding include 当前布局）
- 如果当前的 State 不是 STARTED，那么 return
- API 大于等于 16，走这里，用编舞者 post 一个 FrameCallback 协调 vsync 信号，FrameCallback 就是 mRebindRunnable
- API 小于 16，通过 post 一个 mRebindRunnable
接着看 mRebindRunnable：
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private final Runnable mRebindRunnable = new Runnable() {
@Override
public void run() {
synchronized (this) {
mPendingRebind = false;
}
processReferenceQueue();
if (VERSION.SDK_INT >= VERSION_CODES.KITKAT) {
// Nested so that we don't get a lint warning in IntelliJ
if (!mRoot.isAttachedToWindow()) {
// Don't execute the pending bindings until the View
// is attached again.
mRoot.removeOnAttachStateChangeListener(ROOT_REATTACHED_LISTENER);
mRoot.addOnAttachStateChangeListener(ROOT_REATTACHED_LISTENER);
return;
}
}
executePendingBindings();
}
};
接着看 executePendingBindings()
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public void executePendingBindings() {
if (mContainingBinding == null) {
executeBindingsInternal();
} else {
mContainingBinding.executePendingBindings();
}
}
接着看 executeBindingsInternal()
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private void executeBindingsInternal() {
if (mIsExecutingPendingBindings) {
requestRebind();
return;
}
if (!hasPendingBindings()) {
return;
}
mIsExecutingPendingBindings = true;
mRebindHalted = false;
if (mRebindCallbacks != null) {
mRebindCallbacks.notifyCallbacks(this, REBIND, null);
// The onRebindListeners will change mPendingHalted
if (mRebindHalted) {
mRebindCallbacks.notifyCallbacks(this, HALTED, null);
}
}
if (!mRebindHalted) {
executeBindings();
if (mRebindCallbacks != null) {
mRebindCallbacks.notifyCallbacks(this, REBOUND, null);
}
}
mIsExecutingPendingBindings = false;
}
调用了到了 executeBindings()，这是个抽象的方法，我们的布局都会生成 XXXImple，如 AMainBindingImpl extends AMainBinding
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public class AIncludBindingImpl extends AIncludBinding {
@Override
protected void executeBindings() {
long dirtyFlags = 0;
synchronized(this) {
dirtyFlags = mDirtyFlags;
mDirtyFlags = 0;
}
int catViewModelIsShowNameViewVISIBLEViewINVISIBLE = 0;
me.hacket.assistant.samples.google.architecture.databinding.oneway.CatViewModel catViewModel = mCatViewModel;
java.lang.String catViewModelNameGet = null;
androidx.databinding.ObservableField<java.lang.String> catViewModelName = null;
java.lang.String javaLangStringCatViewModelName = null;
boolean catViewModelIsShowNameGet = false;
androidx.databinding.ObservableBoolean catViewModelIsShowName = null;
if ((dirtyFlags & 0x1eL) != 0) {
if ((dirtyFlags & 0x1aL) != 0) {
if (catViewModel != null) {
// read catViewModel.name
catViewModelName = catViewModel.getName();
}
updateRegistration(1, catViewModelName);
if (catViewModelName != null) {
// read catViewModel.name.get()
catViewModelNameGet = catViewModelName.get();
}
// read ("主布局：") + (catViewModel.name.get())
javaLangStringCatViewModelName = ("主布局：") + (catViewModelNameGet);
}
if ((dirtyFlags & 0x1cL) != 0) {
if (catViewModel != null) {
// read catViewModel.isShowName()
catViewModelIsShowName = catViewModel.isShowName();
}
updateRegistration(2, catViewModelIsShowName);
if (catViewModelIsShowName != null) {
// read catViewModel.isShowName().get()
catViewModelIsShowNameGet = catViewModelIsShowName.get();
}
if((dirtyFlags & 0x1cL) != 0) {
if(catViewModelIsShowNameGet) {
dirtyFlags |= 0x40L;
}
else {
dirtyFlags |= 0x20L;
}
}
// read catViewModel.isShowName().get() ? View.VISIBLE : View.INVISIBLE
catViewModelIsShowNameViewVISIBLEViewINVISIBLE = ((catViewModelIsShowNameGet) ? (android.view.View.VISIBLE) : (android.view.View.INVISIBLE));
}
}
// batch finished
if ((dirtyFlags & 0x10L) != 0) {
// api target 1
this.btnChangeText.setOnClickListener(mCallback8);
this.includeTest.setViewGone(true);
this.includeTest.setCount(100);
}
if ((dirtyFlags & 0x18L) != 0) {
// api target 1
this.includeTest.setCatViewModel2(catViewModel);
}
if ((dirtyFlags & 0x1aL) != 0) {
// api target 1
me.hacket.assistant.samples.google.architecture.databinding.inverse.InverseMethodActivityKt.setText(this.tvNameOb2, javaLangStringCatViewModelName);
}
if ((dirtyFlags & 0x1cL) != 0) {
// api target 1
this.tvNameOb2.setVisibility(catViewModelIsShowNameViewVISIBLEViewINVISIBLE);
}
executeBindingsOn(includeTest);
}
}
- 根据不同的 dirtyFlags 来执行 setter 操作
- 如果 include 其他的布局时，会执行
executeBindingsOn(includeTest);includeTest 就是被 include 的布局的 Binding
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protected static void executeBindingsOn(ViewDataBinding other) {
other.executeBindingsInternal();
}
dirtyFlags 什么时候设置？
在 setter 的时候设置的，mDirtyFlags |= 0x4L 是标志哪个属性变了，notifyPropertyChanged(BR.workBean) 通知对应的 model 有变化。
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public void setWorkBean(@Nullable ObservableWorkBean WorkBean) {
this.mWorkBean = WorkBean;
synchronized (this) {
mDirtyFlags |= 0x4L;
}
notifyPropertyChanged(BR.workBean);
super.requestRebind();
}
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