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【JetPack DataBinding】

程序员文章站 2022-03-11 22:59:49
【JetPack DataBinding】具体使用方法可以查看这个文档然后直接开始源码的分析一、分析生成的布局文件如何适配的我们知道使用框架的时候添加了data的标签,在其中添加了参数,但是实际上布局是不会识别的,有什么作用呢,我们在生成的build文件里找到了如下两个文件可以发现第一个文件已经去除了data标签,同时底部的xml被打上了tag,和第二个文件的xml的tag一一对应,两个文件形成匹配,在apt形成的代码里实际上就是使用第一个布局来进行试图填充档需要增加属性的时候,会使...

【JetPack DataBinding】

具体使用方法可以查看这个文档

然后直接开始源码的分析

一、分析生成的布局文件如何适配的

我们知道使用框架的时候添加了data的标签,在其中添加了参数,但是实际上布局是不会识别的,有什么作用呢,我们在生成的build文件里找到了如下两个文件

可以发现第一个文件已经去除了data标签,同时底部的xml被打上了tag,和第二个文件的xml的tag一一对应,两个文件形成匹配,在apt形成的代码里实际上就是使用第一个布局来进行试图填充

档需要增加属性的时候,会使用第二个布局文件找到相关节点进行替换

【JetPack DataBinding】

【JetPack DataBinding】

 

二、DataBindingUtil类setContentView

在DataBindingUtil下面,这里获取了一个新的底层view,平时写的xml文件是加载到decodeview里面的,们旧的布局文件替换为新的布局文件,新的布局文件

  public static <T extends ViewDataBinding> T setContentView(@NonNull Activity activity,
            int layoutId, @Nullable DataBindingComponent bindingComponent) {
        activity.setContentView(layoutId);
        View decorView = activity.getWindow().getDecorView();
        ViewGroup contentView = (ViewGroup) decorView.findViewById(android.R.id.content);
        return bindToAddedViews(bindingComponent, contentView, 0, layoutId);
    }
//

 private static <T extends ViewDataBinding> T bindToAddedViews(DataBindingComponent component,
            ViewGroup parent, int startChildren, int layoutId) {
        final int endChildren = parent.getChildCount();
        final int childrenAdded = endChildren - startChildren;
        if (childrenAdded == 1) {
            final View childView = parent.getChildAt(endChildren - 1);
            return bind(component, childView, layoutId);
        } else {
            final View[] children = new View[childrenAdded];
            for (int i = 0; i < childrenAdded; i++) {
                children[i] = parent.getChildAt(i + startChildren);
            }
            return bind(component, children, layoutId);
        }
    }

 static <T extends ViewDataBinding> T bind(DataBindingComponent bindingComponent, View root,
            int layoutId) {
        return (T) sMapper.getDataBinder(bindingComponent, root, layoutId);
    }

getDataBinder的方法,我们需要在其实现类里面找,apt帮我们生成了

DataBinderMapperImpl

  @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);
        }
      }
    }
    return null;
  }

这里新建了ActivityMainBindingImpl对象

 public ActivityMainBindingImpl(@Nullable androidx.databinding.DataBindingComponent bindingComponent, @NonNull View root) {
//3代表我们布局文件下多少个节点
        this(bindingComponent, root, mapBindings(bindingComponent, root, 3, sIncludes, sViewsWithIds));
    }


protected static Object[] mapBindings(DataBindingComponent bindingComponent, View root,
            int numBindings, IncludedLayouts includes, SparseIntArray viewsWithIds) {
        Object[] bindings = new Object[numBindings];
        mapBindings(bindingComponent, root, bindings, includes, viewsWithIds, true);
        return bindings;
    }

在这里面将所有的布局节点存在了本地的缓存里,是对xml进行解析保存

在这里对XML文件信息读取,并存入数组中

 private static void mapBindings(DataBindingComponent bindingComponent, View view,
            Object[] bindings, IncludedLayouts includes, SparseIntArray viewsWithIds,
            boolean isRoot) {
        final int indexInIncludes;
        final ViewDataBinding existingBinding = getBinding(view);
        if (existingBinding != null) {
            return;
        }
        Object objTag = view.getTag();
        final String tag = (objTag instanceof String) ? (String) objTag : null;
        boolean isBound = false;
        if (isRoot && tag != null && tag.startsWith("layout")) {
            final int underscoreIndex = tag.lastIndexOf('_');
            if (underscoreIndex > 0 && isNumeric(tag, underscoreIndex + 1)) {
                final int index = parseTagInt(tag, underscoreIndex + 1);
                if (bindings[index] == null) {
                    bindings[index] = view;
                }
                indexInIncludes = includes == null ? -1 : index;
                isBound = true;
            } else {
                indexInIncludes = -1;
            }
        } else if (tag != null && tag.startsWith(BINDING_TAG_PREFIX)) {
            int tagIndex = parseTagInt(tag, BINDING_NUMBER_START);
            if (bindings[tagIndex] == null) {
                bindings[tagIndex] = view;
            }
            isBound = true;
            indexInIncludes = includes == null ? -1 : tagIndex;
        } else {
            // Not a bound view
            indexInIncludes = -1;
        }
        if (!isBound) {
            final int id = view.getId();
            if (id > 0) {
                int index;
                if (viewsWithIds != null && (index = viewsWithIds.get(id, -1)) >= 0 &&
                        bindings[index] == null) {
                    bindings[index] = view;
                }
            }
        }

        if (view instanceof  ViewGroup) {
            final ViewGroup viewGroup = (ViewGroup) view;
            final int count = viewGroup.getChildCount();
            int minInclude = 0;
            for (int i = 0; i < count; i++) {
                final View child = viewGroup.getChildAt(i);
                boolean isInclude = false;
                if (indexInIncludes >= 0 && child.getTag() instanceof String) {
                    String childTag = (String) child.getTag();
                    if (childTag.endsWith("_0") &&
                            childTag.startsWith("layout") && childTag.indexOf('/') > 0) {
                        // This *could* be an include. Test against the expected includes.
                        int includeIndex = findIncludeIndex(childTag, minInclude,
                                includes, indexInIncludes);
                        if (includeIndex >= 0) {
                            isInclude = true;
                            minInclude = includeIndex + 1;
                            final int index = includes.indexes[indexInIncludes][includeIndex];
                            final int layoutId = includes.layoutIds[indexInIncludes][includeIndex];
                            int lastMatchingIndex = findLastMatching(viewGroup, i);
                            if (lastMatchingIndex == i) {
                                bindings[index] = DataBindingUtil.bind(bindingComponent, child,
                                        layoutId);
                            } else {
                                final int includeCount =  lastMatchingIndex - i + 1;
                                final View[] included = new View[includeCount];
                                for (int j = 0; j < includeCount; j++) {
                                    included[j] = viewGroup.getChildAt(i + j);
                                }
                                bindings[index] = DataBindingUtil.bind(bindingComponent, included,
                                        layoutId);
                                i += includeCount - 1;
                            }
                        }
                    }
                }
                if (!isInclude) {
                    mapBindings(bindingComponent, child, bindings, includes, viewsWithIds, false);
                }
            }
        }
    }

至此,需要的信息都保存并解析在我们的build文件里了,所以在主线程我们可以使用bingding.xxx来调用节点

二、setXXX方法

先上一下我们User的Bean类

public class User extends BaseObservable {
    private String name;
    private String pwd;

    public User(String name, String pwd) {
        this.name = name;
        this.pwd = pwd;
    }

    @Bindable
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
        notifyPropertyChanged(BR.name);
    }

    @Bindable
    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
        notifyPropertyChanged(BR.pwd);
    }
}

然后我们来看一下binging.setXXX方法是怎么样实现ui更新的

以setUser举例,在ActivityMainBindingImpl里面有着生成好的方法

public void setUser(@Nullable com.example.databindi ngdemo_20210117.User User) {
        updateRegistration(0, User);
        this.mUser = User;
        synchronized(this) {
            mDirtyFlags |= 0x1L;
        }
        notifyPropertyChanged(BR.user);
        super.requestRebind();
    }

ViewDataBinding

CreateWeakListener是一个回调,属性发生变化,监听器会被执行

localFieldId是我们每一个属性的id,这里我们是setUser,也就是对应BR文件的user的id,想一下如果没有一个id,我们咋知道是哪一个呢,所以是作为标识用的

mLocalFieldObservers数组使用了BR做下标,使用数组绑定了每一个属性对应的监听器,监听器激活就会通知ui更新

 protected boolean updateRegistration(int localFieldId, Observable observable) {
        return updateRegistration(localFieldId, observable, CREATE_PROPERTY_LISTENER);
    }

 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;
    }

   protected void registerTo(int localFieldId, Object observable,
            CreateWeakListener listenerCreator) {
        if (observable == null) {
            return;
        }
        WeakListener listener = mLocalFieldObservers[localFieldId];
        if (listener == null) {
            listener = listenerCreator.create(this, localFieldId);
            mLocalFieldObservers[localFieldId] = listener;
            if (mLifecycleOwner != null) {
                listener.setLifecycleOwner(mLifecycleOwner);
            }
        }
//这里添加的
        listener.setTarget(observable);
    }
//绑定了监听器
   public void setTarget(T object) {
            unregister();
            mTarget = object;
            if (mTarget != null) {
                mObservable.addListener(mTarget);
            }
        }

这里的listener寻找其实现方法,就是添加我们的User实体类到内存里,别忘了User是实现了BaseObservable 的类,User是作为Observe观察者被一层一层传递到内存里进行注册和监听器进行绑定的

如下:

  private static class WeakPropertyListener extends Observable.OnPropertyChangedCallback
            implements ObservableReference<Observable> {
        final WeakListener<Observable> mListener;

        public WeakPropertyListener(ViewDataBinding binder, int localFieldId) {
            mListener = new WeakListener<Observable>(binder, localFieldId, this);
        }

        @Override
        public WeakListener<Observable> getListener() {
            return mListener;
        }

        @Override
        public void addListener(Observable target) {
//在这里调用,并且添加
            target.addOnPropertyChangedCallback(this);
        }

        @Override
        public void removeListener(Observable target) {
            target.removeOnPropertyChangedCallback(this);
        }

        @Override
        public void setLifecycleOwner(LifecycleOwner lifecycleOwner) {
        }

        @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);
        }
    }

然后addOnPropertyChangedCallback会调用到User类实现的BaseObservable里面去

    @Override
    public void addOnPropertyChangedCallback(@NonNull OnPropertyChangedCallback callback) {
        synchronized (this) {
            if (mCallbacks == null) {
                mCallbacks = new PropertyChangeRegistry();
            }
        }
        mCallbacks.add(callback);
    }

这里的callback实际上就是我们的observe

 

看一下类图

我们的ViewDataBinding里面是有WeakListener监听器数组的,他的监听器在我们BaseObservable里面也持有他的引用,

当set方法调用,我们最后就会new PropertyChangeRgistry,相当于将BaseObservable和我们传入的listener进行某种程度上的绑定,

实际上是BaseObservable调用的时候,会把id传进来,通过id来徐兆监听器,然后去给ui进行更新

一堆对象和对象的绑定关系在上述代码中被绑定起来了

【JetPack DataBinding】

如何更新ui

notifyPropertyChanged
public void setUser(@Nullable com.example.databindi ngdemo_20210117.User User) {
        updateRegistration(0, User);
        this.mUser = User;
        synchronized(this) {
            mDirtyFlags |= 0x1L;
        }
        notifyPropertyChanged(BR.user);
        super.requestRebind();
    }

一层一层点击下去就会到

public class PropertyChangeRegistry extends CallbackRegistry<OnPropertyChangedCallback, Observable, Void> {
    private static final NotifierCallback<OnPropertyChangedCallback, Observable, Void> NOTIFIER_CALLBACK = new NotifierCallback<OnPropertyChangedCallback, Observable, Void>() {
        public void onNotifyCallback(OnPropertyChangedCallback callback, Observable sender, int arg, Void notUsed) {
            callback.onPropertyChanged(sender, arg);
        }
    };

    public PropertyChangeRegistry() {
        super(NOTIFIER_CALLBACK);
    }

    public void notifyChange(@NonNull Observable observable, int propertyId) {
        this.notifyCallbacks(observable, propertyId, (Object)null);
    }
}

通过以下的调用链条,我们找到了

mCallbacks.notifyCallbacks() --- notifiRecurse()---notifyRemainder()---notifyFirst64()---notifyCallbacks()---mNotifier.onNotifyCallback()---PropertyChangeRegistry类中调用onPropertyChanged()方法

ViewDataBinding中实现

通过监听器处理数据变化与UI更新
handleFieldChange--》ActivityMainBindingImpl.onFieldChange()

 @Override
    protected boolean onFieldChange(int localFieldId, Object object, int fieldId) {
        switch (localFieldId) {
            case 0 :
                return onChangeUser((com.example.databindingdemo_20210117.User) object, fieldId);
        }
        return false;
    }
    private boolean onChangeUser(com.example.databindingdemo_20210117.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;
        }
        else if (fieldId == BR.pwd) {
            synchronized(this) {
                    mDirtyFlags |= 0x4L;
            }
            return true;
        }
        return false;
    }

onFieldChange()方法的实现在ActivityMainBindingImpl.java中

如果onFieldChange()返回真,则执行requestRebind,意思就是有数据更新,就会返回true,同时通过或操作完成了id的定位

再回到 setUser里面的super.requestRebind();这里有一个runnable对象

protected void requestRebind() {
        if (mContainingBinding != null) {
            mContainingBinding.requestRebind();
        } else {
            final LifecycleOwner owner = this.mLifecycleOwner;
            if (owner != null) {
                Lifecycle.State state = owner.getLifecycle().getCurrentState();
                if (!state.isAtLeast(Lifecycle.State.STARTED)) {
                    return; // wait until lifecycle owner is started
                }
            }
            synchronized (this) {
                if (mPendingRebind) {
                    return;
                }
                mPendingRebind = true;
            }
            if (USE_CHOREOGRAPHER) {
                mChoreographer.postFrameCallback(mFrameCallback);
            } else {
                mUIThreadHandler.post(mRebindRunnable);
            }
        }
    }
 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();
        }
    };

然后我们一路走下去executePendingBindings()--executeBindingsInternal()---executeBindings()---executeBindings();的实现找ActivityMainBindingImpl类

最终走到核心类

@Override
    protected void executeBindings() {
        long dirtyFlags = 0;
        synchronized(this) {
            dirtyFlags = mDirtyFlags;
            mDirtyFlags = 0;
        }
        java.lang.String userName = null;
        com.example.databindingdemo_20210117.User user = mUser;
        java.lang.String userPwd = null;

        if ((dirtyFlags & 0xfL) != 0) {


            if ((dirtyFlags & 0xbL) != 0) {//1011   0010

                    if (user != null) {
                        // read user.name
                        userName = user.getName();
                    }
            }
            if ((dirtyFlags & 0xdL) != 0) {//1101    0100

                    if (user != null) {
                        // read user.pwd
                        userPwd = user.getPwd();
                    }
            }
        }
        // batch finished
        if ((dirtyFlags & 0xbL) != 0) {
            // api target 1

            androidx.databinding.adapters.TextViewBindingAdapter.setText(this.tv1, userName);
        }
        if ((dirtyFlags & 0xdL) != 0) {
            // api target 1

            androidx.databinding.adapters.TextViewBindingAdapter.setText(this.tv2, userPwd);
        }
    }

之前的mDirtyFlags会发生与运算,以此来判断是哪一个id,使用这种操作可以提升性能,

最后调用settext来设置ui,完成了所有流程

@BindingAdapter("android:text")
    public static void setText(TextView view, CharSequence text) {
        final CharSequence oldText = view.getText();
        if (text == oldText || (text == null && oldText.length() == 0)) {
            return;
        }
        if (text instanceof Spanned) {
            if (text.equals(oldText)) {
                return; // No change in the spans, so don't set anything.
            }
        } else if (!haveContentsChanged(text, oldText)) {
            return; // No content changes, so don't set anything.
        }
        view.setText(text);
    }

最后来一个原理图

 【JetPack DataBinding】

User做为observal和生成的布局文件的impl类进行交流,impl里存储了我们实体类的字段id,同时和weakprepertyListener进行绑定,当触发了id操作的时候,就会在impl里寻找对应id,触发listener,listener就会触发apt生成的方法来进行设置操作,最终完成

发出通知的操作是setXXXX方法

如果一开始没有调用怎么更新,在对应的ViewDatabinding里,有和页面绑定的方法,直接回触发runnable

binding.mRebindRunnable.run();之后就是上面的流程了。

  private static final OnAttachStateChangeListener ROOT_REATTACHED_LISTENER;

    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) {
                }
            };
        }
    }

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

本文地址:https://blog.csdn.net/czZ__czZ/article/details/112834696

相关标签: android