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原理：
Glide.with(this)绑定了Activity的生命周期。在Activity内新建了一个无UI的Fragment，这个Fragment持有一个Lifecycle，通过Lifecycle在Fragment关键生命周期通知RequestManager进行相关从操作。在生命周期onStart时继续加载，onStop时暂停加载，onDestory时停止加载任务和清除操作。
面试官：glide调用在子线程会怎么样？
在UI线程中调用Glide，在子线程使用的话会和使用ApplicationContext一样；
可以理解为不对请求的生命周期进行管理
1、传入Application Context或者在子线程使用：调用getApplicationManager(context);这样Glide的生命周期就和应用程序一样了。可以理解为不对请求的生命周期进行管理
关键的几个类：RequestManager，RequestManagerRetriever ，SupportRequestManagerFragment ，
Lifecycle ，LifecycleListener
public class MainActivityextends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Glide.with(MainActivity.this);
}
}
public class Glide {
private static Glideglide;
private Glide() {
}
public static synchronized GlidegetInstance() {
if (glide ==null) {
glide =new Glide();
}
return glide;
}
@NonNull
public static RequestManagerwith(@NonNull FragmentActivity activity) {
return getRetriever(activity).get(activity);
}
@NonNull
private static RequestManagerRetrievergetRetriever(@Nullable Context context) {
return new RequestManagerRetriever();
}
/***
* 1.里面是对RequestManager的封装，用fragment生命周期，还是application的生命周期
* 2.里面绑定fragment和RequestManager
*/
public class RequestManagerRetriever {
private volatile RequestManagerapplicationManager;
@NonNull
public RequestManagerget(@NonNull Context context) {
if (context ==null) {
throw new IllegalArgumentException("You cannot start a load on a null Context");
}else if (Util.isOnMainThread() && !(contextinstanceof Application)) {
if (contextinstanceof FragmentActivity) {
return get((FragmentActivity) context);
}else if (contextinstanceof Activity) {
return get((Activity) context);
}else if (contextinstanceof ContextWrapper
&& ((ContextWrapper) context).getBaseContext().getApplicationContext() !=null) {
return get(((ContextWrapper) context).getBaseContext());
}
}
return getApplicationManager(context);
}
public RequestManagerget(FragmentActivity activity) {
if (Util.isOnBackgroundThread()) {
return get(activity.getApplicationContext());
}else {
FragmentManager fm = activity.getSupportFragmentManager();
return supportFragmentGet(activity, fm, null, false);
}
}
/***
* 绑定逻辑都在这里
* @param context
* @param fm
* @param parentHint
* @param isParentVisible
* @return
*/
@NonNull
private RequestManagersupportFragmentGet(
@NonNull Context context,
@NonNull FragmentManager fm,
@Nullable Fragment parentHint,
boolean isParentVisible) {
SupportRequestManagerFragment current =null;
RequestManager requestManager = current.getRequestManager();
if (requestManager ==null) {
Glide glide = Glide.getInstance();
requestManager =new RequestManager(glide,current.getGlideLifecycle());
current.setRequestManager(requestManager);
}
return requestManager;
}
@NonNull
private RequestManagergetApplicationManager(@NonNull Context context) {
if (applicationManager ==null) {
return applicationManager;
}
return applicationManager;
}
}
/***
* fragment里面设置了requestManager:
* 里面把ActivityFragmentLifecycle监听回调出去
*/
public class SupportRequestManagerFragmentextends Fragment {
private final ActivityFragmentLifecyclelifecycle;
@Nullable
private RequestManagerrequestManager;
public SupportRequestManagerFragment(ActivityFragmentLifecycle lifecycle) {
this.lifecycle = lifecycle;
}
public RequestManagergetRequestManager() {
return requestManager;
}
public void setRequestManager(RequestManager requestManager) {
this.requestManager = requestManager;
}
@NonNull
ActivityFragmentLifecyclegetGlideLifecycle() {
return lifecycle;
}
@Override
public void onStart() {
super.onStart();
lifecycle.onStart();
}
@Override
public void onStop() {
super.onStop();
lifecycle.onStop();
}
@Override
public void onDestroy() {
super.onDestroy();
lifecycle.onDestroy();
}
}
public class RequestManagerimplements LifecycleListener {
Lifecyclelifecycle;
public RequestManager(Glide glide, ActivityFragmentLifecycle glideLifecycle) {
lifecycle = glideLifecycle;
register();
}
public RequestManager() {
}
public void register() {
lifecycle.addListener(RequestManager.this);
}
@Override
public void onStart() {
}
@Override
public void onStop() {
}
@Override
public void onDestroy() {
}
}
public interface LifecycleListener {
/**
* Callback for when {@link android.app.Fragment#onStart()}} or {@link
*/
void onStart();
/**
* Callback for when {@link android.app.Fragment#onStop()}} or {@link
*/
void onStop();
/**
* Callback for when {@link android.app.Fragment#onDestroy()}} or {@link
*/
void onDestroy();
}
public interface Lifecycle {
void addListener(@NonNull LifecycleListener listener);
void removeListener(@NonNull LifecycleListener listener);
}
class ActivityFragmentLifecycleimplements Lifecycle {
private final SetlifecycleListeners =
Collections.newSetFromMap(new WeakHashMap());
private boolean isStarted;
private boolean isDestroyed;
@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);
}
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();
}
}
}
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