Glide RequestManagerFragment
Glide.width(context)都做了些什么
public static RequestManager with(Activity activity) {
RequestManagerRetriever retriever = RequestManagerRetriever.get();
return retriever.get(activity);
}
Retriever是猎犬的意思,我认为RequestManagerRetriever是享元模式，只要width()里的参数是同一个对象，它拿到的一定是同一个RequestManager。
而它并不会去把RequestManager存在自己的成员当中,而是用了一个Fragment，存于FragmentManager当中，而此Fragment如果没有RequestManger，则会new一个RequestManager;
而用Fragment的好处是能不通过用户告知就知道当前界面的生命周期，有点神出鬼没有没有！！
@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
public RequestManager get(android.app.Fragment fragment) {
if (fragment.getActivity() == null) {
throw new IllegalArgumentException("You cannot start a load on a fragment..");
}
if (Util.isOnBackgroundThread() || Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
return get(fragment.getActivity().getApplicationContext());
} else {
android.app.FragmentManager fm = fragment.getChildFragmentManager();
return fragmentGet(fragment.getActivity(), fm);
}
}
@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
RequestManagerFragment getRequestManagerFragment(final android.app.FragmentManager fm) {
RequestManagerFragment current = (RequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
if (current == null) {
current = pendingRequestManagerFragments.get(fm);
if (current == null) {
current = new RequestManagerFragment();
pendingRequestManagerFragments.put(fm, current);
fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();
}
}
return current;
}
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
RequestManager fragmentGet(Context context, android.app.FragmentManager fm) {
RequestManagerFragment current = getRequestManagerFragment(fm);
RequestManager requestManager = current.getRequestManager();
if (requestManager == null) {
Log.d("seekting", "RequestManagerRetriever.重新创建requestManager");
requestManager = new RequestManager(context, current.getLifecycle(),//...ignore code
current.setRequestManager(requestManager);
} else {
Log.d("seekting", "RequestManagerRetriever.利用以前的requestManager");
}
return requestManager;
}
有一个小知识点，为什么会有一段这样的代码：
handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();想想如果在一个Fragment里多次调用Glide.with().因为commitAllowingStateLoss之后，并不能立马findFragmentByTag找到，所以作者需要先把它存起来，等能找到的时候再将它行色移出去.
RequestManagerRetriever拿requestManager,requestManager有很多种:
如:Activity,fragment,application,FragmentActivity
RequestManager如何撑控生命周期
注：fragment和fragmentActivity的话，它会创建对应的Fragment提交给FragmentManager，也就是说它丫用了一个Fragment去保存一个requestManager,而这个Fragment又被FragmentManager 持有.这里面还用到了pendingRequestManagerFragments，主要是 fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();之后，不会立码被find到.
实现LifecycleListener(onStart(),onStop(),onDesory())接口，
承载RequestManager的fragment首先会创建一个ActivityFragmentLifecycle,
Fragment的生命周期会转交给ActivityFragmentLifecycle，而ActivityFragmentLifecycle会告诉它的listener现在Fragment所处的生命周期，此listener就是RequestManager,最终RequestManager得到了Fragment的生命周期。
这个设计很绕,可以用时序图来表示：
RequestManagerFragment的成员
private final ActivityFragmentLifecycle lifecycle;//为了告诉RequestManager它的生命周期
private final RequestManagerTreeNode requestManagerTreeNode = new FragmentRequestManagerTreeNode();
private RequestManager requestManager;
private final HashSet<RequestManagerFragment> childRequestManagerFragments
= new HashSet<RequestManagerFragment>();
private RequestManagerFragment rootRequestManagerFragment;
先看rootRequestManagerFragment,它是Activity的根节点
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
rootRequestManagerFragment = RequestManagerRetriever.get()
.getSupportRequestManagerFragment(getActivity().getSupportFragmentManager());
if (rootRequestManagerFragment != this) {
rootRequestManagerFragment.addChildRequestManagerFragment(this);
}
}
@Override
public void onDetach() {
super.onDetach();
if (rootRequestManagerFragment != null) {
rootRequestManagerFragment.removeChildRequestManagerFragment(this);
rootRequestManagerFragment = null;
}
}
通过getActivity().getSupportFragmentManager()拿Activity级的RequestFragment,然后判断是否相等，如果不相等，显然就是child.
同时onDetach的时候把child remove掉.
childRequestManagerFragments和rootRequestManagerFragment用来做什么的呢？
原来是为FragmentRequestManagerTreeNode服务的,而TreeNode最终会被RequestManager的resumeRequestsRecursive()方法所用.
但是此方法Glide内部没有调用，是公开给接入者用的.
public void resumeRequestsRecursive() {
Util.assertMainThread();
resumeRequests();
for (RequestManager requestManager : treeNode.getDescendants()) {
requestManager.resumeRequests();
}
}
public void pauseRequestsRecursive() {
Util.assertMainThread();
pauseRequests();
for (RequestManager requestManager : treeNode.getDescendants()) {
requestManager.pauseRequests();
}
}
RequestManagerFragment有两个设计有点让人觉得曲折:
1.为什么要通过ActivityFragmentLifecycle把生命周期通过ActivityFragmentLifecycle传给RequestManager.而不直接通过自己持有RequestManager然后调用RequestManager的onStart,onStop
或许通过这个中间层能突出一个生命周期模块，且好扩展；另外就是GenericRequestBuilder也用到了lifeCycle
2.为什么要通过一个内部类TreeNode来把所有的descendants交给处部?
或许这样能让外部更少的知道fragment而通过treeNode访问一个api,也就是最少知道原则
getDescendantRequestManagerFragments方法有点问题
/**
* Returns the set of fragments that this RequestManagerFragment's parent is a parent to. (i.e. our parent is
* the fragment that we are annotating).
*/
public Set<SupportRequestManagerFragment> getDescendantRequestManagerFragments() {
if (rootRequestManagerFragment == null) {
return Collections.emptySet();
} else if (rootRequestManagerFragment == this) {
return Collections.unmodifiableSet(childRequestManagerFragments);
} else {
HashSet<SupportRequestManagerFragment> descendants =
new HashSet<SupportRequestManagerFragment>();
for (SupportRequestManagerFragment fragment
: rootRequestManagerFragment.getDescendantRequestManagerFragments()) {
if (isDescendant(fragment.getParentFragment())) { //此处为什么要传parent
descendants.add(fragment);
}
}
return Collections.unmodifiableSet(descendants);
}
}
/**
* Returns true if the fragment is a descendant of our parent.
*/
private boolean isDescendant(Fragment fragment) {
Fragment root = this.getParentFragment();
while (fragment.getParentFragment() != null) {
if (fragment.getParentFragment() == root) {
return true;
}
fragment = fragment.getParentFragment();
}
return false;
}
此api明明是想把和自己父亲是同一个祖先的孩子都加到列表里来，但是为什么要加getParent,也就是说任何一个fragment,它的爷爷(或爷爷以上级别)和this的父亲相同，就该加进set; 换句话说，就是任意fragment的爸爸（或爸爸以上）是this，就加进set，这样理解没问题，然而还有一种情况: A>B>C C>E>F C>D>G 如果C用两个子Fragment，如果this是D,fragment是F，F的爷爷是D的爸爸，那F也和D扯上关系，我觉得不合理 另外值得注意的地方是，它返回的是unmodifiableSet，unmodifiableSet是不让再add和remove的
private static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
private static final long serialVersionUID = 1820017752578914078L;
final Collection<E> c;
UnmodifiableCollection(Collection<E> collection) {
c = collection;
}
@Override public boolean add(E object) {
throw new UnsupportedOperationException();
}
@Override public boolean addAll(Collection<? extends E> collection) {
throw new UnsupportedOperationException();
}
@Override public void clear() {
throw new UnsupportedOperationException();
}
@Override public boolean contains(Object object) {
return c.contains(object);
}
@Override public boolean containsAll(Collection<?> collection) {
return c.containsAll(collection);
}
@Override public boolean isEmpty() {
return c.isEmpty();
}
@Override public Iterator<E> iterator() {
return new Iterator<E>() {
Iterator<E> iterator = c.iterator();
@Override public boolean hasNext() {
return iterator.hasNext();
}
@Override public E next() {
return iterator.next();
}
@Override public void remove() {
throw new UnsupportedOperationException();
}
};
}
@Override public boolean remove(Object object) {
throw new UnsupportedOperationException();
}
@Override public boolean removeAll(Collection<?> collection) {
throw new UnsupportedOperationException();
}
@Override public boolean retainAll(Collection<?> collection) {
throw new UnsupportedOperationException();
}
@Override public int size() {
return c.size();
}
@Override public Object[] toArray() {
return c.toArray();
}
@Override public <T> T[] toArray(T[] array) {
return c.toArray(array);
}
@Override public String toString() {
return c.toString();
}
}