主頁：http://cherylgood.cn/c/Android開發之CoordinatorLayout使用詳解一.php
官網描述爲：CoordinatorLayout是一個增強版的FrameLayout（繼承自ViewGroup）
用途：
1、作爲應用的頂層視圖。
2、作爲一個可以指定子View之間相互作用的容器，通過給CoordinatorLayout的子View指定CoordinatorLayout.Behavior 來定義子view之間的相互作用。（你可以想象成：CoordinatorLayout相當於在兩個View之間充當中介,這樣子的好處就是兩個view之間的耦合度降低了，只需要跟coordinatorLayout打交到即可，而CoordinatorLayout.Behavior 相當於兩個view之間的協議，即通過怎樣的規則來約束雙方的行爲。）
設計概念：
- CoordinatorLayout：CoordinatorLayout 作爲最頂層視圖，將負責管理所有的子view，使其內部的子View彼此間產生一種聯繫。這個聯繫通過Behavior來實現（包括了滑動狀態的處理以及View狀態的處理）。
- AppBarLayout：AppBarLayout 繼承自限性佈局，作爲增強版的線性佈局，他增加了對滑動手勢的處理。
- Behavior：Behavior 是google新提出的，能夠讓你以非侵入式的方式去處理目標View和其他View的交互行爲。Behavior需要設置在觸發事件（比如滾動）的view上，且這個View必須是CoordinatorLayout的第一層級下的子view，否則沒有效果，因爲Behavior的初始化是在CoordinatorLayout的LayoutParams中通過反射完成的。
Behavior實例化方式：1、通過app:layout_behavior聲明 ；2、在你的自定義View類上添加@DefaultBehavior(MyBehavior.class)； - Behavior只是個接口，其調用是由NestedScrollingParent與NestedScrollingChild接口負責調用。
接下來我們通過閱讀部分源碼進行學習：
首先，我們從兩個view是如何通過coordinatorlayout產生關聯來入手；看代碼
LayoutParams(Context context, AttributeSet attrs) {
super(context, attrs);
final TypedArray a = context.obtainStyledAttributes(attrs,
R.styleable.CoordinatorLayout_Layout);
this.gravity = a.getInteger(
R.styleable.CoordinatorLayout_Layout_android_layout_gravity,
Gravity.NO_GRAVITY);
mAnchorId = a.getResourceId(R.styleable.CoordinatorLayout_Layout_layout_anchor,
View.NO_ID);
this.anchorGravity = a.getInteger(
R.styleable.CoordinatorLayout_Layout_layout_anchorGravity,
Gravity.NO_GRAVITY);
this.keyline = a.getInteger(R.styleable.CoordinatorLayout_Layout_layout_keyline,
-1);
insetEdge = a.getInt(R.styleable.CoordinatorLayout_Layout_layout_insetEdge, 0);
dodgeInsetEdges = a.getInt(
R.styleable.CoordinatorLayout_Layout_layout_dodgeInsetEdges, 0);
mBehaviorResolved = a.hasValue(
R.styleable.CoordinatorLayout_Layout_layout_behavior);
if (mBehaviorResolved) {
mBehavior = parseBehavior(context, attrs, a.getString(
R.styleable.CoordinatorLayout_Layout_layout_behavior));
}
a.recycle();
if (mBehavior != null) {
// If we have a Behavior, dispatch that it has been attached
mBehavior.onAttachedToLayoutParams(this);
}
}
從
mBehaviorResolved = a.hasValue(
R.styleable.CoordinatorLayout_Layout_layout_behavior);
if (mBehaviorResolved) {
mBehavior = parseBehavior(context, attrs, a.getString(
R.styleable.CoordinatorLayout_Layout_layout_behavior));
}
這幾句我們可以看到。 mBehaviorResolved 是個boolean 變量，如果
R.styleable.CoordinatorLayout_Layout_layout_behavior CoordinatorLayout的
layout_behavior這個字段設置有值， 1、mBehaviorResolved = true -》調用parseBehavior方法，將所需參數傳入通過java的反射技術返回一個Behavior實例。
static Behavior parseBehavior(Context context, AttributeSet attrs, String name) {
if (TextUtils.isEmpty(name)) {
return null;
}
final String fullName;
if (name.startsWith(".")) {
// Relative to the app package. Prepend the app package name.
fullName = context.getPackageName() + name;
} else if (name.indexOf('.') >= 0) {
// Fully qualified package name.
fullName = name;
} else {
// Assume stock behavior in this package (if we have one)
fullName = !TextUtils.isEmpty(WIDGET_PACKAGE_NAME)
? (WIDGET_PACKAGE_NAME + '.' + name)
: name;
}
try {
Map<String, Constructor> constructors = sConstructors.get();
if (constructors == null) {
constructors = new HashMap<>();
sConstructors.set(constructors);
}
Constructor c = constructors.get(fullName);
if (c == null) {
final Class clazz = (Class) Class.forName(fullName, true,
context.getClassLoader());
c = clazz.getConstructor(CONSTRUCTOR_PARAMS);
c.setAccessible(true);
constructors.put(fullName, c);
}
return c.newInstance(context, attrs);
} catch (Exception e) {
throw new RuntimeException("Could not inflate Behavior subclass " + fullName, e);
}
}
通過這一段我們可以知道，最後是通過調用Behavior的參數爲(context,attrs)的構造函數進行實例化。 實例化出Behavior之後我們會調用behavior的onAttachedToLayoutParams方法 將LayoutParams的實例對象傳進去mBehavior.onAttachedToLayoutParams(this);
mBehavior.onAttachedToLayoutParams是一個當LayoutParams被實例化後的回調方法。 通過這裏，我們的
CoordinatorLayout就能夠跟用layout_behavior標識的子View產生聯繫。 當子View發生變化時，CoordinatorLayout又是如何處理的的，請看下面代碼：
final void onChildViewsChanged(@DispatchChangeEvent final int type) {
final int layoutDirection = ViewCompat.getLayoutDirection(this);
final int childCount = mDependencySortedChildren.size();
final Rect inset = acquireTempRect();
final Rect drawRect = acquireTempRect();
final Rect lastDrawRect = acquireTempRect();
for (int i = 0; i < childCount; i++) {
final View child = mDependencySortedChildren.get(i);
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
if (type == EVENT_PRE_DRAW && child.getVisibility() == View.GONE) {
// Do not try to update GONE child views in pre draw updates.
continue;
}
// Check child views before for anchor
for (int j = 0; j < i; j++) {
final View checkChild = mDependencySortedChildren.get(j);
if (lp.mAnchorDirectChild == checkChild) {
offsetChildToAnchor(child, layoutDirection);
}
}
// Get the current draw rect of the view
getChildRect(child, true, drawRect);
// Accumulate inset sizes
if (lp.insetEdge != Gravity.NO_GRAVITY && !drawRect.isEmpty()) {
final int absInsetEdge = GravityCompat.getAbsoluteGravity(
lp.insetEdge, layoutDirection);
switch (absInsetEdge & Gravity.VERTICAL_GRAVITY_MASK) {
case Gravity.TOP:
inset.top = Math.max(inset.top, drawRect.bottom);
break;
case Gravity.BOTTOM:
inset.bottom = Math.max(inset.bottom, getHeight() - drawRect.top);
break;
}
switch (absInsetEdge & Gravity.HORIZONTAL_GRAVITY_MASK) {
case Gravity.LEFT:
inset.left = Math.max(inset.left, drawRect.right);
break;
case Gravity.RIGHT:
inset.right = Math.max(inset.right, getWidth() - drawRect.left);
break;
}
}
// Dodge inset edges if necessary
if (lp.dodgeInsetEdges != Gravity.NO_GRAVITY && child.getVisibility() == View.VISIBLE) {
offsetChildByInset(child, inset, layoutDirection);
}
if (type == EVENT_PRE_DRAW) {
// Did it change? if not continue
getLastChildRect(child, lastDrawRect);
if (lastDrawRect.equals(drawRect)) {
continue;
}
recordLastChildRect(child, drawRect);
}
// Update any behavior-dependent views for the change
for (int j = i + 1; j < childCount; j++) {
final View checkChild = mDependencySortedChildren.get(j);
final LayoutParams checkLp = (LayoutParams) checkChild.getLayoutParams();
final Behavior b = checkLp.getBehavior();
if (b != null && b.layoutDependsOn(this, checkChild, child)) {
if (type == EVENT_PRE_DRAW && checkLp.getChangedAfterNestedScroll()) {
// If this is from a pre-draw and we have already been changed
// from a nested scroll, skip the dispatch and reset the flag
checkLp.resetChangedAfterNestedScroll();
continue;
}
final boolean handled;
switch (type) {
case EVENT_VIEW_REMOVED:
// EVENT_VIEW_REMOVED means that we need to dispatch
// onDependentViewRemoved() instead
b.onDependentViewRemoved(this, checkChild, child);
handled = true;
break;
default:
// Otherwise we dispatch onDependentViewChanged()
handled = b.onDependentViewChanged(this, checkChild, child);
break;
}
if (type == EVENT_NESTED_SCROLL) {
// If this is from a nested scroll, set the flag so that we may skip
// any resulting onPreDraw dispatch (if needed)
checkLp.setChangedAfterNestedScroll(handled);
}
}
}
}
releaseTempRect(inset);
releaseTempRect(drawRect);
releaseTempRect(lastDrawRect);
}
我們可以看到文檔說明，大概意思是當子view發生變化會調用該方法。該方法會遍歷所有的子view， 然後調用如下代碼，layoutDependsOn（）這個方法是做什麼的呢？我們接下來看下該方法。
if (b != null && b.layoutDependsOn(this, checkChild, child)) {
if (type == EVENT_PRE_DRAW && checkLp.getChangedAfterNestedScroll()) {
// If this is from a pre-draw and we have already been changed
// from a nested scroll, skip the dispatch and reset the flag
checkLp.resetChangedAfterNestedScroll();
continue;
}
final boolean handled;
switch (type) {
case EVENT_VIEW_REMOVED:
// EVENT_VIEW_REMOVED means that we need to dispatch
// onDependentViewRemoved() instead
b.onDependentViewRemoved(this, checkChild, child);
handled = true;
break;
default:
// Otherwise we dispatch onDependentViewChanged()
handled = b.onDependentViewChanged(this, checkChild, child);
break;
}
if (type == EVENT_NESTED_SCROLL) {
// If this is from a nested scroll, set the flag so that we may skip
// any resulting onPreDraw dispatch (if needed)
checkLp.setChangedAfterNestedScroll(handled);
}
}
/**
* Determine whether the supplied child view has another specific sibling view as a
* layout dependency.
*
*
This method will be called at least once in response to a layout request. If it * returns true for a given child and dependency view pair, the parent CoordinatorLayout * will:
*
- *
- Always lay out this child after the dependent child is laid out, regardless * of child order.
- *
- Call {@link #onDependentViewChanged} when the dependency view's layout or * position changes.
- *
*
* @param parent the parent view of the given child
* @param child the child view to test
* @param dependency the proposed dependency of child
* @return true if child's layout depends on the proposed dependency's layout,
* false otherwise
*
* @see #onDependentViewChanged(CoordinatorLayout, android.view.View, android.view.View)
*/
public boolean layoutDependsOn(CoordinatorLayout parent, V child, View dependency) {
return false;
}
這個方法，大概意思是如果我們返回true，說明當前發生變化的子view發生變化時。也就是該方法決定我們用
layout_behavior標識的view是否應該做出相應的變化。默認返回false，該方法需要我們在創建自己的Behavior時重寫。 當返回true的話，可以看到會調用
b.onDependentViewRemoved(this, checkChild, child);
handled = b.onDependentViewChanged(this, checkChild, child); 爲了更好理解這兩句代碼，我們舉個例子，假設有ViewA和ViewB ，當ViewB發生移動時，ViewA要向反方向移動。 1、當ViewB被移除時會調用
b.onDependentViewRemoved(this, checkChild, child); 2、當ViewB發生變化時，會調用
handled = b.onDependentViewChanged(this, checkChild, child); 那麼我們就可以在
b.onDependentViewChanged裏面寫我們的功能代碼了。 通過以上的分析，希望能幫到大家對CoordinatorLayout的協作調用過程有一些些的幫助。
http://cherylgood.cn/c/Android開發之CoordinatorLayout使用詳解二.php