Activity创立ViewModel

创立ViewModel

// MyActivity#onCreate()
val mainViewModel = 
            [V1]   ViewModelProvider(this)
              [V2]       .get(MainViewModel::class.java)

[V1]

ViewModelProvider结构函数

// androidx.lifecycle.ViewModelProvider#get(java.lang.Class<T>)
    public constructor(
        owner: ViewModelStoreOwner
    ) : this(owner.viewModelStore, defaultFactory(owner), defaultCreationExtras(owner))

this指MyActivity，即MyActivity应该是[I]ViewModelStoreOwner类型

MyActivity承继[C]ComponentActivity]，ComponentActivity完成了[I]ViewModelStoreOwner接口

// CompnentActivity
public class ComponentActivity extends androidx.core.app.ComponentActivity implements
        // ...
        ViewModelStoreOwner,
        // ... {

this(owner.viewModelStore, defaultFactory(owner), defaultCreationExtras(owner)) ，这儿运用 owner.viewModelStore从ViewModelStoreOwner中取出[OC]ViewModelStore]

// ViewModelStoreOwner
interface ViewModelStoreOwner {
    /**
     * The owned [ViewModelStore]
     */
    val viewModelStore: ViewModelStore
}

然后调用下面的结构函数

// ViewModelStoreOwner
/**
 * Creates a ViewModelProvider
 *
 * @param store `ViewModelStore` where ViewModels will be stored.
 * @param factory factory a `Factory` which will be used to instantiate new `ViewModels`
 * @param defaultCreationExtras extras to pass to a factory
 */
@JvmOverloads
constructor(
    private val store: ViewModelStore,
    private val factory: Factory,
    private val defaultCreationExtras: CreationExtras = CreationExtras.Empty,
) {

[V2]

调用了get办法⬇️

// androidx.lifecycle.ViewModelProvider#get(java.lang.Class<T>)
    @MainThread
    public open operator fun <T : ViewModel> get(modelClass: Class<T>): T {
        val canonicalName = modelClass.canonicalName
            ?: throw IllegalArgumentException("Local and anonymous classes can not be ViewModels")
   [W1]  return get("$DEFAULT_KEY:$canonicalName", modelClass)
    }

[W1]

// androidx.lifecycle.ViewModelProvider#get(java.lang.String, java.lang.Class<T>)
    @MainThread
    public open operator fun <T : ViewModel> get(key: String, modelClass: Class<T>): T {
    [X1]val viewModel = store[key]
    [X1]if (modelClass.isInstance(viewModel)) {
            ....
    [X1]    return viewModel as T
        ....
    [X2]return try {
    [X2]     factory.create(modelClass, extras)
    [X2] catch (e: AbstractMethodError) {
    [X2]    factory.create(modelClass)
    [X2]}.also { store.put(key, it) }
    }

[X1]⬅️[W1]

从store([OC]ViewModelStore)中能找到viewmodel则直接回来
[X2]⬅️[W1]

store中找不到则需要新创立一个viewmodel并放入store，这儿说明只需运用同一个ViewModelStore获取ViewModel则不同当地获取到的都是同一个ViewModel

[OC]ViewModelStore看起来是个Map，事实上他的完成便是保护一个map，放出get和put办法
```
open class ViewModelStore {
    private val map = mutableMapOf<String, ViewModel>()
    ...
    fun put(key: String, viewModel: ViewModel) {
    }
    operator fun get(key: String): ViewModel? {
        return map[key]
    }
    ...
}
```

总结上面，Activity在onCreate时创立viewModel，Activity是一个ViewModelStoreOwner其间有一个ViewModelStore其间保护一个map，ViewModelProvier作为一个工具类在运用默许的/我们供给的Factory（为了适配结构函数有参的ViewModel）创立ViewModel的一起会将其存入这个map。

所以，在relaunch过程中，毁掉旧的Activity时假如能保存它的mViewModelStore，然后将其赋值新的Activity的mViewModelStore就能完成装备改变viewModel不改变的效果。

Activity重建ViewModel坚持存在的完成

relaunch之后新的Activity获取之前的viewModel

viewModel存在ViewModelStore中，说明ViewModelStore在Activity重建的过程中能坚持存在，看下[C]ComponentActivity怎么怎么获取[OC]ViewModelStore的

    public ViewModelStore getViewModelStore() {
        if (getApplication() == null) {
            throw new IllegalStateException("Your activity is not yet attached to the "
                    + "Application instance. You can't request ViewModel before onCreate call.");
        }
   [T1] ensureViewModelStore();
        return mViewModelStore;
    }

[T1]

在getViewModelStore()办法中调用了ensureViewModelStore()保证mViewModelStore不为空

    @SuppressWarnings("WeakerAccess") /* synthetic access */
    void ensureViewModelStore() {
        if (mViewModelStore == null) {
        [U1] NonConfigurationInstances nc =
                    (NonConfigurationInstances) getLastNonConfigurationInstance();
            if (nc != null) {
                // Restore the ViewModelStore from NonConfigurationInstances
        [U2]    mViewModelStore = nc.viewModelStore;
            }
            if (mViewModelStore == null) {
                mViewModelStore = new ViewModelStore();
            }
        }
    }

[U1]⬅️[T1]

// Activity
    @Nullable
    public Object getLastNonConfigurationInstance() {
        return mLastNonConfigurationInstances != null
                ? mLastNonConfigurationInstances.activity : null;
    }

Activirty.mLastNonConfigurationInstances类型为[C]Activity.NonConfigurationInstances

// android.app.Activity.NonConfigurationInstances
    static final class NonConfigurationInstances {
        Object activity;
        ....
    }

mLastNonConfigurationInstances.activity在[U1]⬅️[T1]处被强转为[C]ComponentActivity.NonConfigurationInstances

// androidx.activity.ComponentActivity.NonConfigurationInstances
    static final class NonConfigurationInstances {
        Object custom;
        ViewModelStore viewModelStore;
    }

[U2]⬅️[T1]

假如[U1]获取的nc不为空，则将mViewModelStore赋值为nc.viewModelStore 即Activity.mLastNonConfigurationInstances.activity.viewModelStore

所以想要保存给新Activity运用本来的viewModel，重点便是要在relaunch过程中保存旧的Activity.mLastNonConfigurationInstances然后再赋值给新Activity.mLastNonConfigurationInstances

relaunch过程中保存旧Activity的viewModel

设备改变，系统调用AMS的updateConfiguration 办法

ActivityManagerService.java – Android Code Search

// ActivityManagerService
    @Override
    public boolean updateConfiguration(Configuration values) {
        return mActivityTaskManager.updateConfiguration(values);
    }

// ActivityTaskManagerService
    @Override
    public boolean updateConfiguration(Configuration values) {
           ....
                updateConfigurationLocked(values, null, false, false /* persistent */,
           ....
    }

// ActivityTaskManagerService
    boolean updateConfigurationLocked(Configuration values, ActivityRecord starting,
            boolean initLocale, boolean persistent, int userId, boolean deferResume,
            ActivityTaskManagerService.UpdateConfigurationResult result) {
            ....
            「I1」  changes = updateGlobalConfigurationLocked(values, initLocale, persistent, userId);
            ....
            「I2」 kept = ensureConfigAndVisibilityAfterUpdate(starting, changes);
            ....
    }

「I1」

updateGlobalConfigurationLocked 更新当时装备信息

「I2」

ensureConfigAndVisibilityAfterUpdate 保证给定的activity更新运用的装备

这儿starting传入的是null，需要ensureConfigAndVisibilityAfterUpdate中自己获取

// ActivityTaskManagerService
    boolean ensureConfigAndVisibilityAfterUpdate(ActivityRecord starting, int changes) {
        boolean kept = true;
     「J1」   final Task mainRootTask = mRootWindowContainer.getTopDisplayFocusedRootTask();
        ....
             「J2」 starting = mainRootTask.topRunningActivity();
        ....
             「J3」 kept = starting.ensureActivityConfiguration(changes,
        ....
    }

「J1」⬅️「I2」

获取根窗口容器中当时具有焦点的尖端任务（root task）
「J2」⬅️「I2」

获取尖端任务（root task）中当时正在运转的尖端Activity（top running Activity）的ActivityRecord赋值给starting

「J3」⬅️「I2」

ActivityRecord对应的Activity更新Configuration

// com.android.server.wm.ActivityRecord#ensureActivityConfiguration(int, boolean)
    boolean ensureActivityConfiguration(int globalChanges, boolean preserveWindow) {
        return ensureActivityConfiguration(globalChanges, preserveWindow,
                false /* ignoreVisibility */);
    }

// com.android.server.wm.ActivityRecord#ensureActivityConfiguration(int, boolean, boolean)
    boolean ensureActivityConfiguration(int globalChanges, boolean preserveWindow,
            boolean ignoreVisibility) {
            ....
                relaunchActivityLocked(preserveWindow);
            ....
    }

 // com.android.server.wm.ActivityRecord#relaunchActivityLocked
    void relaunchActivityLocked(boolean preserveWindow) {
            ....
       「K2」  final ClientTransactionItem callbackItem = ActivityRelaunchItem.obtain(pendingResults,
            ....
       「K1」  final ClientTransaction transaction = ClientTransaction.obtain(app.getThread(), token);
       「K2」  transaction.addCallback(callbackItem);
            ....
       「K3」  mAtmService.getLifecycleManager().scheduleTransaction(transaction);
            ....
    }

「K1」⬅️「J3」

token来自[C]ActivityRecord承继的[C]WindowToken中的token

class WindowToken extends WindowContainer<WindowState> {
    private static final String TAG = TAG_WITH_CLASS_NAME ? "WindowToken" : TAG_WM;
    /** The actual token */
    final IBinder token;
    /** The type of window this token is for, as per {@link WindowManager.LayoutParams} */
    final int windowType;

 // ClientTransaction
    /** Obtain an instance initialized with provided params. */
    public static ClientTransaction obtain(IApplicationThread client, IBinder activityToken) {
        ClientTransaction instance = ObjectPool.obtain(ClientTransaction.class);
        if (instance == null) {
            instance = new ClientTransaction();
        }
        instance.mClient = client;
        instance.mActivityToken = activityToken;
        return instance;
    }

将transaction.mActivityToken设置为ActivityRecord.token

「K2」⬅️「J3」

给transaction放入callback：[C]ActivityRelaunchItem

「K3」⬅️「J3」

履行transaction

// com.android.server.wm.ClientLifecycleManager#scheduleTransaction(ClientTransaction)
    void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
        ....
        transaction.schedule();
        ....
    }

// ClientTransaction
    public void schedule() throws RemoteException {
   「L1」  mClient.scheduleTransaction(this);
    }

「L1」⬅️「K3」

[C]ClientTransaction运用mClient履行自己

mClient是什么?

// ClientTransaction
    /** Target client. */
    private IApplicationThread mClient;

这儿是运用AIDL(根据Binder)进行进程间通信，对应文件IApplicationThread.aidl⬇️

oneway interface IApplicationThread {
    ....
    void scheduleTransaction(in ClientTransaction transaction);

这儿mClient是客户端，对应的客户端为[c]ApplicationThread

    private class ApplicationThread extends IApplicationThread.Stub {

「M1」⬅️「L1」

所以下面从 android.app.ActivityThread.ApplicationThread#scheduleTransaction办法继续

// android.app.ActivityThread.ApplicationThread#scheduleTransaction
        @Override
        public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
            ActivityThread.this.scheduleTransaction(transaction);
        }

这儿scheduleTransaction是调用的ActivityThread的基类ClientTransactonHandler中的scheduleTransaction办法

// android.app.ClientTransactionHandler#scheduleTransaction
    void scheduleTransaction(ClientTransaction transaction) {
 「N1」  transaction.preExecute(this);
 「N2」  sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);
    }

「N1」⬅️「M1」

为后面transaction的履行做些预备，这儿this传入的是[C]ActivityThread

    public void preExecute(android.app.ClientTransactionHandler clientTransactionHandler) {
        if (mActivityCallbacks != null) {
            ....
            for (int i = 0; i < size; ++i) {
            「O1」  mActivityCallbacks.get(i).preExecute(clientTransactionHandler, mActivityToken);
            ....
    }

「O1」⬅️「N1」

履行每个callback的preExecute办法，callback只有一个之前在「K2」处放入的ActivityRelaunchItem

 // android.app.servertransaction.ActivityRelaunchItem#preExecute
    public void preExecute(ClientTransactionHandler client, IBinder token) {
    「P1」 mActivityClientRecord = client.prepareRelaunchActivity(token, mPendingResults,
                mPendingNewIntents, mConfigChanges, mConfig, mPreserveWindow);
    }

「P1」⬅️ 「O1」

从ActivityThread(即client)获取要relaunch的ActivityRecord存入ActivityRelaunchItem.mActivityClientRecord

    @Override
    public ActivityClientRecord prepareRelaunchActivity(IBinder token,
            List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents,
            int configChanges, MergedConfiguration config, boolean preserveWindow) {
    「Q1」     ....
    「Q2」     target = new ActivityClientRecord();
    「Q2」     target.token = token;
                ....
    「Q3」     mRelaunchingActivities.add(target);
                ....
        return ....target....;
    }

「Q1」⬅️「P1」

检查是否方针activity是否现已正在relaunch了，假如是则回来
「Q2」⬅️「P1」

方针activity没有现已正在relaunch（这儿认为是没有，这个判别只是为了避免relaunch正在relaunch的activity），则结构一个[sC]ActivityClientRecord记录要relaunch的Activity的token等信息

「Q3」⬅️「P1」运用ActivityThread.mRelaunchingActivities记录一切要预备重启的ActivityClientRecord

+-----------------------------------------------------+
|                                                     |
|                 ActivityThread                      |
|                                                     |
|       +-----------------------------------+         |
|       |    mRelaunchingActivities         |         |
|       |                                   |         |
|       |   +------------------------+      |         |
|       |   | ActivityClientRecord   |      |         |
|       |   +------------------------+      |         |
|       |                                   |         |
|       |   +------------------------+      |         |
|       |   | ActivityClientRecord   |      |         |
|       |   +------------------------+      |         |
|       |                                   |         |
|       |           ....                    |         |
|       |                                   |         |
|       |                                   |         |
|       +-----------------------------------+         |
|                                                     |
+-----------------------------------------------------+

「N2」⬅️「M1」

这儿运用Handler去真实履行transaction，obj传入的便是transaction

// android.app.ClientTransactionHandler#sendMessage
    abstract void sendMessage(int what, Object obj);

// android.app.ActivityThread#sendMessage(int, java.lang.Object)
    void sendMessage(int what, Object obj) {
        sendMessage(what, obj, 0, 0, false);
    }

⬇️结构Message

// android.app.ActivityThread#sendMessage(int, java.lang.Object, int, int, boolean)
    private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) {
        ....
        msg.what = what;
        msg.obj = obj;
        ....
        mH.sendMessage(msg);
    }

⬇️handler：ActivityThread.H 收到音讯并处理

// android.app.ActivityThread.H#handleMessage
        public void handleMessage(Message msg) {
            ...
             switch (msg.what) {
                ...
                case EXECUTE_TRANSACTION:
              「R1」  final ClientTransaction transaction = (ClientTransaction) msg.obj;
              「R2」  mTransactionExecutor.execute(transaction);
                    ....

「R1」⬅️「N2」从message中取出transaction

「R2」⬅️「N2」交给mTransactionExecutor履行

mTransactionHandler 是谁？是[C]ActivityThread，从TransactionExecutor的结构函数⬇️中能够看出

// ActivityThread
    private final TransactionExecutor mTransactionExecutor = new TransactionExecutor(this);

    /** Initialize an instance with transaction handler, that will execute all requested actions. */
    public TransactionExecutor(ClientTransactionHandler clientTransactionHandler) {
        mTransactionHandler = clientTransactionHandler;
    }

TransactionExecutor.mTransactionHandler是对持有该TransactionExecutor的ActivityThread的引证

+-------------------------------------------------------------------------------------+
|                                    ActivityThread <-------+                         |
|                                                           |                         |
|                                                           |                         |
|      +-----------------------------------------------------------------+            |
|      |  mTransactionExecutor: TransactionExecutor         |            |            |
|      |                                                    |            |            |
|      |                                                    |            |            |
|      |  +-------------------------------------------------+---------+  |            |
|      |  |   mTransactionHandler: ClientTransactionHandler           |  |            |
|      |  |                                                           |  |            |
|      |  |                                                           |  |            |
|      |  +-----------------------------------------------------------+  |            |
|      |                                                                 |            |
|      |                                                                 |            |
|      +-----------------------------------------------------------------+            |
|                                                                                     |
+-------------------------------------------------------------------------------------+

// android.app.servertransaction.TransactionExecutor#execute
    public void execute(ClientTransaction transaction) {
        ....
        executeCallbacks(transaction);
        ....
    }

// android.app.servertransaction.TransactionExecutor#executeCallbacks
    public void executeCallbacks(ClientTransaction transaction) {
        final List<ClientTransactionItem> callbacks = transaction.getCallbacks();
        ....
  「S1」 final IBinder token = transaction.getActivityToken();
        ....
        for (int i = 0; i < size; ++i) {
            final ClientTransactionItem item = callbacks.get(i);
            ....
    「S2」  item.execute(mTransactionHandler, token, mPendingActions);
            ....
    }

「S1」⬅️「R2」

从transaction中获取activityToken「K1」⬅️「J3」

「S2」⬅️「R2」

callback（为ActivityRelaunchItem）履行，execute办法来自ActivityRelaunchItem 完成的接口BaseClientRequest的execute办法

至于mTransactionHandler是谁，在「R2」现已解释

execute办法来自ActivityRelaunchItem完成的接口BaseClientRequest中的execute办法⬇️

public interface BaseClientRequest extends ObjectPoolItem {
    ....
    void execute(ClientTransactionHandler client, IBinder token,
            PendingTransactionActions pendingActions);
    ....
}

ActivityRelaunchItem和BaseClientRequest的关系⬇️

public abstract class ClientTransactionItem implements BaseClientRequest

public abstract class ActivityTransactionItem extends ClientTransactionItem

public class ActivityRelaunchItem extends ActivityTransactionItem

classDiagram
      class ClientTransactionItem {
      }
      class ActivityTransactionItem {
      }
      class ActivityRelaunchItem {
      }
      class BaseClientRequest {
         <<interface>>
         + execute(ClientTransactionHandler client, IBinder token,PendingTransactionActions pendingActions)
      }
      ClientTransactionItem <|-- ActivityTransactionItem
      ActivityTransactionItem <|-- ActivityRelaunchItem
      BaseClientRequest <|-- ClientTransactionItem: implements

该execute办法由[C]ActivityRelaunchItem的基类ActivityTransactionItem完成

// ActivityTransactionItem
    public final void execute(ClientTransactionHandler client, IBinder token,
            PendingTransactionActions pendingActions) {
   「A1」  final ActivityClientRecord r = getActivityClientRecord(client, token);
   「A2」  execute(client, r, pendingActions);
    }

「A1」根据token获取ActivityClientRecord

// ActivityTransactionItem
    @NonNull ActivityClientRecord getActivityClientRecord(
            @NonNull ClientTransactionHandler client, IBinder token) {
        final ActivityClientRecord r = client.getActivityClient(token);
        ....
        return r;
    }

client是 TransactionExecutor.mTransactionHandler，也便是持有TransactionExecutor的ActivityThread

// ActivityThread 
    @Override
    public ActivityClientRecord getActivityClient(IBinder token) {
        return mActivities.get(token);
    }

「A2」继续履行 ⬇️

// ActivityRelaunchItem
    @Override
    public void execute(ClientTransactionHandler client, ActivityClientRecord r,
            PendingTransactionActions pendingActions) {
        ....
  「B1」  client.handleRelaunchActivity(mActivityClientRecord, pendingActions);
    }

「B1」mActivityClientRecord从哪里来？之前「P1」⬅️ 「O1」

// ActivityThread
    @Override
    public void handleRelaunchActivity(ActivityClientRecord tmp,
            PendingTransactionActions pendingActions) {
        ...
    「C1」 ActivityClientRecord r = mActivities.get(tmp.token);
        ...
    「C2」handleRelaunchActivityInner(r, configChanges, tmp.pendingResults, tmp.pendingIntents,
                pendingActions, tmp.startsNotResumed, tmp.overrideConfig, "handleRelaunchActivity");
        ...
    }

「C1」⬅️「B1」

这儿从mActivities中根据token获取[sC]ActivityClientRecord

+----------------------------------------------------------------+
|   ActivityThread                                               |
|                                                                |
|                                                                |
|    +------------------------------------------------------+    |
|    |  mActivities                                         |    |
|    |             +--------------------------------------+ |    |
|    |             |      +---------------+               | |    |
|    |             |      |    Activity   |               | |    |
|    |             |      +---------------+               | |    |
|    |             |                                      | |    |
|    |             |   +-------------------------------+  | |    |
|    |             |   | lastNonConfigurationInstances |  | |    |
|    |             |   +-------------------------------+  | |    |
|    |             |                                      | |    |
|    |             +--------------------------------------+ |    |
|    |             +--------------------------------------+ |    |
|    |             |                                      | |    |
|    |             |                                      | |    |
|    |             +--------------------------------------+ |    |
|    |             +--------------------------------------+ |    |
|    |             |                                      | |    |
|    |             |                                      | |    |
|    |             +--------------------------------------+ |    |
|    |                                                      |    |
|    |                           ...                        |    |
|    |                                                      |    |
|    +------------------------------------------------------+    |
+----------------------------------------------------------------+

「C2」⬅️「B1」

传递r给

// ActivityThread
    private void handleRelaunchActivityInner(ActivityClientRecord r, int configChanges,
            List<ResultInfo> pendingResults, List<ReferrerIntent> pendingIntents,
            PendingTransactionActions pendingActions, boolean startsNotResumed,
            Configuration overrideConfig, String reason) {
        ...
「D1」        handleDestroyActivity(r, false, configChanges, true, reason);
        ...
「D2」        handleLaunchActivity(r, pendingActions, customIntent);
    }

「D1」⬅️「C2」

⬇️Destroy本来的Activity，其间getNonConfigInstance传入了true

// ActivityThread
    @Override
    public void handleDestroyActivity(ActivityClientRecord r, boolean finishing, int configChanges,
            boolean getNonConfigInstance, String reason) {
        performDestroyActivity(r, finishing, configChanges, getNonConfigInstance, reason);
        ...
    }

⬇️将本来的activity的nonConfigurationInstances存入ActivityRecord.lastNonConfigurationInstances

// ActivityThread
    /** Core implementation of activity destroy call. */
    void performDestroyActivity(ActivityClientRecord r, boolean finishing,
            int configChanges, boolean getNonConfigInstance, String reason) {
        ...
    「E1」 if (getNonConfigInstance) {
            ....
            「E2」  r.lastNonConfigurationInstances = r.activity.retainNonConfigurationInstances();
            ....

「E1」这儿假如是getNonConfigInstance为true（前面传的是true），

「E2」

则️将[sC]ActivityClientRecord中放入Java 代码块的成果，其间就包括viewModelStore

 // Activity
    NonConfigurationInstances retainNonConfigurationInstances() {
「F1」 Object activity = onRetainNonConfigurationInstance();
        ...
        NonConfigurationInstances nci = new NonConfigurationInstances();
        nci.activity = activity;
        ....
        return nci;
    }

「F1」Activity默许完成中只回来了null，可是[C]ComponentActivity重写了这个办法⬇️

 // ComponentActivity
    public final Object onRetainNonConfigurationInstance() {
        // Maintain backward compatibility.
「G1」  Object custom = onRetainCustomNonConfigurationInstance();
        ViewModelStore viewModelStore = mViewModelStore;
「G2」  if (viewModelStore == null) {
            ....
        }
        ....
「G3」   NonConfigurationInstances nci = new NonConfigurationInstances();
        nci.custom = custom;
        nci.viewModelStore = viewModelStore;
        return nci;
    }

「G1」我们能够经过重写onRetainCustomNonConfigurationInstance()创立custom即自定义的在configuration改变后仍然想要保存的数据。
「G2」这儿当viewModelStore为空的时分会检查[C]ComponentActivity.NonConfigurationInstances中是否有viewModelStore，这儿对应从来没有当地调用过getViewModelStore，也就不会初始化ComponentActivity.mVieModelStore，可是我们这儿状况是之前有创立viewmodel，this(owner.viewModelStore, defaultFactory(owner), defaultCreationExtras(owner)) ，这儿运用 owner.viewModelStore从ViewModelStoreOwner中取出[OC]ViewModelStore调用过，一切不会走到viewModelStore == null的分支
「G3」这儿创立了[C]ComponentActivity.NonConfigurationInstances存入 custom和viewModelStore并回来。

「D2」⬅️「C2」履行LaunchActivity

// android.app.ActivityThread#handleLaunchActivity
    public Activity handleLaunchActivity(ActivityClientRecord r,
            PendingTransactionActions pendingActions, Intent customIntent) {
        ....
        final Activity a = performLaunchActivity(r, customIntent);
        ....
        return a;
    }

// android.app.ActivityThread#performLaunchActivity
    private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
        ....
        Activity activity = null;
        try {
            java.lang.ClassLoader cl = appContext.getClassLoader();
      「H1」 activity = mInstrumentation.newActivity(
                    cl, component.getClassName(), r.intent);
            ....
        try {
            ....
            if (activity != null) {
                ....
        「H2」   activity.attach(appContext, this, getInstrumentation(), r.token,
                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                        r.embeddedID, r.lastNonConfigurationInstances, config,
                        r.referrer, r.voiceInteractor, window, r.activityConfigCallback,
                        r.assistToken, r.shareableActivityToken);
        ....
        return activity;
    }

「H1」

实例化一个Activity
「H2」

运用本来的ActivityRecord给Activity设置参数，其间第12个参数便是在「E2」处保存的lastNonConfigurationInstances，其间就有viewModel

这儿就回答了上面[U2]处的问题，串起来了

reference

code

Android 面试总结 – ViewModel 是怎么保存和康复？ – ()
Android Framework之Activity启动流程(一) | 柚子 | pomeloJiang
Zygote的启动流程 – ()
Android屏幕旋转源码探索及使用实践 | 奔哲明的博客 (benzblog.site)
Configuration 改变时Activity的生命周期探求 – ()

ViewModel旋转屏幕仍然保持存在原理

目录

Activity创立ViewModel

Activity重建ViewModel坚持存在的完成

relaunch之后新的Activity获取之前的viewModel

relaunch过程中保存旧Activity的viewModel

reference

作者信息

推广

ViewModel旋转屏幕仍然保持存在原理

目录

Activity创立ViewModel

Activity重建ViewModel坚持存在的完成

relaunch之后新的Activity获取之前的viewModel

relaunch过程中保存旧Activity的viewModel

reference

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