Android开发SavedState Jetpack状态保存利器

if(savedStateRegistry.isRestored){
    val consumeRestoredStateForKey = savedStateRegistry.consumeRestoredStateForKey("test")
    val test = consumeRestoredStateForKey?.getInt("test")
    Log.i("hello","tag test is $test")
}
savedStateRegistry.registerSavedStateProvider("test",DataProvider())

class DataProvider: SavedStateRegistry.SavedStateProvider {
    override fun saveState(): Bundle {
        return Bundle().apply {
            this.putInt("test",1)
        }
    }
}

@MainThread
public void registerSavedStateProvider(@NonNull String key,
        @NonNull SavedStateProvider provider) {
    SavedStateProvider previous = mComponents.putIfAbsent(key, provider);
    if (previous != null) {
        throw new IllegalArgumentException("SavedStateProvider with the given key is"
                  " already registered");
    }
}

private SafeIterableMap<String, SavedStateProvider> mComponents =
        new SafeIterableMap<>();

@MainThread
void performSave(@NonNull Bundle outBundle) {
    Bundle components = new Bundle();
    if (mRestoredState != null) {
        components.putAll(mRestoredState);
    }
    for (Iterator<Map.Entry<String, SavedStateProvider>> it =
            mComponents.iteratorWithAdditions(); it.hasNext(); ) {
        Map.Entry<String, SavedStateProvider> entry1 = it.next();
        // 触发了SavedStateProvider的saveState方法
        components.putBundle(entry1.getKey(), entry1.getValue().saveState());
    }
    outBundle.putBundle(SAVED_COMPONENTS_KEY, components);
}

private static final String SAVED_COMPONENTS_KEY =
        "androidx.lifecycle.BundlableSavedStateRegistry.key";

@MainThread
public void performSave(@NonNull Bundle outBundle) {
    mRegistry.performSave(outBundle);
}

@CallSuper
@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
    Lifecycle lifecycle = getLifecycle();
    if (lifecycle instanceof LifecycleRegistry) {
        ((LifecycleRegistry) lifecycle).setCurrentState(Lifecycle.State.CREATED);
    }
    super.onSaveInstanceState(outState);
   被调用 
   mSavedStateRegistryController.performSave(outState);
    mActivityResultRegistry.onSaveInstanceState(outState);
}

@MainThread
@Nullable
public Bundle consumeRestoredStateForKey(@NonNull String key) {
    if (!mRestored) {
        throw new IllegalStateException("You can consumeRestoredStateForKey "
                  "only after super.onCreate of corresponding component");
    }
    if (mRestoredState != null) {
        Bundle result = mRestoredState.getBundle(key);
        mRestoredState.remove(key);
        if (mRestoredState.isEmpty()) {
            mRestoredState = null;
        }
        return result;
    }
    return null;
}

@SuppressWarnings("WeakerAccess")
@MainThread
void performRestore(@NonNull Lifecycle lifecycle, @Nullable Bundle savedState) {
    if (mRestored) {
        throw new IllegalStateException("SavedStateRegistry was already restored.");
    }
    if (savedState != null) {
        mRestoredState = savedState.getBundle(SAVED_COMPONENTS_KEY);
    }
    .... 
    mRestored = true;
}

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    // Restore the Saved State first so that it is available to
    // OnContextAvailableListener instances
   //这里就是恢复数据来源 
   mSavedStateRegistryController.performRestore(savedInstanceState);
    mContextAwareHelper.dispatchOnContextAvailable(this);
    super.onCreate(savedInstanceState);
    mActivityResultRegistry.onRestoreInstanceState(savedInstanceState);
    ReportFragment.injectIfNeededIn(this);
    if (mContentLayoutId != 0) {
        setContentView(mContentLayoutId);
    }
}