Glide源码浅析（四）生命周期下的请求
在RequestManagerRetriever中创建了Fragment并与ReqyestManager相关联
RequestManagerRetriever#fragmentGet():
@NonNull
private RequestManager fragmentGet(@NonNull Context context,
@NonNull android.app.FragmentManager fm,
@Nullable android.app.Fragment parentHint) {
RequestManagerFragment current = getRequestManagerFragment(fm, parentHint);
RequestManager requestManager = current.getRequestManager();
if (requestManager == null) {
// TODO(b/27524013): Factor out this Glide.get() call.
Glide glide = Glide.get(context);
requestManager =
factory.build(
glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
current.setRequestManager(requestManager);
}
return requestManager;
}
首先通过getRequestManagerFragment创建了一个Fragment，首次创建的话，fragment里面并没有包含requestManager,所以hui进入判断体
通过factory创建一个RequestManager
RequestManagerFactory不用多说，用于创建RequestManager
Lifecycle 有两个子类 ApplicationLifecycle和ActivityFragmentLifecycle，ApplicationLifecycle只有一个开始的监听，因为是全局所以只有在应用退出的时候才会有停止状态，ActivityFragmentLifecycle则有开始、停止和销毁三种情况，并且还又移除监听的接口，分别在fragment的onStart()onstop()和onDestroy()进行调用
RquestManagerFragment#
@Override
public void onStart() {
super.onStart();
lifecycle.onStart();
}
@Override
public void onStop() {
super.onStop();
lifecycle.onStop();
}
@Override
public void onDestroy() {
super.onDestroy();
lifecycle.onDestroy();
}
ActivityFragmentLifecycle#
void onStart() {
isStarted = true;
for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {
lifecycleListener.onStart();
}
}
void onStop() {
isStarted = false;
for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {
lifecycleListener.onStop();
}
}
void onDestroy() {
isDestroyed = true;
for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {
lifecycleListener.onDestroy();
}
}
我们可以看到每一个生命周期里面都会调用lifecyclerListener中对应的方法，
@Override
public void addListener(@NonNull LifecycleListener listener) {
lifecycleListeners.add(listener);
if (isDestroyed) {
listener.onDestroy();
} else if (isStarted) {
listener.onStart();
} else {
listener.onStop();
}
}
@Override
public void removeListener(@NonNull LifecycleListener listener) {
lifecycleListeners.remove(listener);
}
ActivityFragmentLifecycle提供了新增和删除监听的两个方法
addListener
在RequestManager的构造器中 调用了这个方法
if (Util.isOnBackgroundThread()) {
mainHandler.post(addSelfToLifecycle);
} else {
lifecycle.addListener(this);
}
lifecycle.addListener(connectivityMonitor);
如果是在主线程中加载的图片，会将RequestManager自身加入监听，并且会加入一个connectivityMonitor监听
ConnectivityMonitorFactory 创建网络监听的工厂类，子类为DefaultConnectivityMonitorFactory
DefaultConnectivityMonitorFactory#build():
@NonNull
@Override
public ConnectivityMonitor build(
@NonNull Context context,
@NonNull ConnectivityMonitor.ConnectivityListener listener) {
int permissionResult = ContextCompat.checkSelfPermission(context, NETWORK_PERMISSION);
boolean hasPermission = permissionResult == PackageManager.PERMISSION_GRANTED;
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(
TAG,
hasPermission
? "ACCESS_NETWORK_STATE permission granted, registering connectivity monitor"
: "ACCESS_NETWORK_STATE permission missing, cannot register connectivity monitor");
}
return hasPermission
? new DefaultConnectivityMonitor(context, listener) : new NullConnectivityMonitor();
}
这里会根据是否有网络权限来创建两个不同的类监听器，NullConnectivityMonitor没有任何的逻辑实现 DefaultConnectivityMonitor
DefaultConnectivityMonitor#...
@Override
public void onStart() {
register();
}
@Override
public void onStop() {
unregister();
}
@Override
public void onDestroy() {
// Do nothing.
}
private final BroadcastReceiver connectivityReceiver = new BroadcastReceiver() {
@Override
public void onReceive(@NonNull Context context, Intent intent) {
boolean wasConnected = isConnected;
isConnected = isConnected(context);
if (wasConnected != isConnected) {
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "connectivity changed, isConnected: " + isConnected);
}
listener.onConnectivityChanged(isConnected);
}
}
};
注册和反注册就是针对网络观察者，网络发生变化之后会调用listener.onConnectivityChanged()
在RequestManager的构造器中：
connectivityMonitor =
factory.build(
context.getApplicationContext(),
new RequestManagerConnectivityListener(requestTracker));
RequestManager#
private static class RequestManagerConnectivityListener implements ConnectivityMonitor
.ConnectivityListener {
private final RequestTracker requestTracker;
RequestManagerConnectivityListener(@NonNull RequestTracker requestTracker) {
this.requestTracker = requestTracker;
}
@Override
public void onConnectivityChanged(boolean isConnected) {
if (isConnected) {
requestTracker.restartRequests();
}
}
}
根据网络的连接状态进行处理，如果是连接状态则调用requestTracker.restartRequests();
RequestTracker 源码中的注释表述的很完全：用于跟踪、取消和重新启动在已完成和失败的请求的类，并且只能在主线程中访问。
RequestTracker#restartRequests():
public void restartRequests() {
for (Request request : Util.getSnapshot(requests)) {
if (!request.isComplete() && !request.isCancelled()) {
// Ensure the request will be restarted in onResume.
request.pause();
if (!isPaused) {
request.begin();
} else {
pendingRequests.add(request);
}
}
}
}
首先遍历请求集合，如果遍历到的秦秋没有完成也没有被取消，那么就先暂停，如果此时的请求正在执行，那么就重新启动，如果此时的 请求本来就再暂停状态,那么就放入到等待队列中
removeListener
RequestManager本身实现了Lifecycle接口，所以就实现了onStart()、onStop()、onDestroy()
RequestManager#onDestroy():
@Override
public void onDestroy() {
targetTracker.onDestroy();
for (Target<?> target : targetTracker.getAll()) {
clear(target);
}
targetTracker.clear();
requestTracker.clearRequests();
lifecycle.removeListener(this);
lifecycle.removeListener(connectivityMonitor);
mainHandler.removeCallbacks(addSelfToLifecycle);
glide.unregisterRequestManager(this);
}
fragment销毁的时候会做一些释放操作，清除所有与当前Fragment有关系的请求,请求所有的监听器
onStart
当fragment走到onStart的时候,会调用RequestManager的resumeRequests()，进而调用RequestTracker.resumeRequests()
这里先说一下RequestTracker中的请求集合
RequestBuilder#into()
private <Y extends Target<TranscodeType>> Y into(
@NonNull Y target,
@Nullable RequestListener<TranscodeType> targetListener,
@NonNull RequestOptions options) {
Util.assertMainThread();
Preconditions.checkNotNull(target);
if (!isModelSet) {
throw new IllegalArgumentException("You must call #load() before calling #into()");
}
options = options.autoClone();
Request request = buildRequest(target, targetListener, options);
Request previous = target.getRequest();
if (request.isEquivalentTo(previous)
&& !isSkipMemoryCacheWithCompletePreviousRequest(options, previous)) {
request.recycle();
// If the request is completed, beginning again will ensure the result is re-delivered,
// triggering RequestListeners and Targets. If the request is failed, beginning again will
// restart the request, giving it another chance to complete. If the request is already
// running, we can let it continue running without interruption.
if (!Preconditions.checkNotNull(previous).isRunning()) {
// Use the previous request rather than the new one to allow for optimizations like skipping
// setting placeholders, tracking and un-tracking Targets, and obtaining View dimensions
// that are done in the individual Request.
previous.begin();
}
return target;
}
requestManager.clear(target);
target.setRequest(request);
requestManager.track(target, request);
return target;
}
这个方法大家应该很属性把，就是Glide调用链的最后一步，设置Imageview；在这里面会先创建一个请求，或是从target中获取一个请求，然后调用requestManager.track()将target和request传过去
RequestManager#track()
void track(@NonNull Target<?> target, @NonNull Request request) {
targetTracker.track(target);
requestTracker.runRequest(request);
}
这里涉及到了一个targetTracke,作用同requestTracker一样，也实现了LifecyclerListener,不过并没有具体的实现，当然我们可以自定义Target,然后等到界面stop的时候不显示图片start的时候显示图片，虽然毫无意义，并且targetTracker同样将Target储存到了一个集合中
我们主要是看requestTracker
RequestTracker#runRequest():
public void runRequest(@NonNull Request request) {
requests.add(request);
if (!isPaused) {
request.begin();
} else {
pendingRequests.add(request);
}
}
可以看到根据当前的请求状态，对请求进行执行或是加入等待队列操作
我们来看onStart状态下的请求处理
RequestTracker#resumeRequesets():
public void resumeRequests() {
isPaused = false;
for (Request request : Util.getSnapshot(requests)) {
if (!request.isComplete() && !request.isCancelled() && !request.isRunning()) {
request.begin();
}
}
pendingRequests.clear();
}
所有的请求开始执行
onStop
@Override
public void onStop() {
for (Target<?> target : Util.getSnapshot(targets)) {
target.onStop();
}
}
stop就非常的简单了
简答总结下：
先创建一个Fragment 然后在创建一个RequestManager,并将Fragment中的Lifecycle传入到RequestManager中，用于传递fragment的声明周期，Lifecycle中包含有一个生命周期的监听，fragment在生命周期切换的时候会间接的调用这个生命周期监听,而实现在RequestManager中，这样就将两个类关联了起来。而RequestManager本身实现了Lifecycle接口，所以其内部实现了onstart()、onStop()的方法;此外还有一个网络监听器ConnectivityMonitor,用于判断当前的网络状态;RequsetBuilder在设置into的时候会将Request间接的传递到RequestTracker中,便于在onStart()、onStop中进行处理
