Save State

Save State

Activity:

/**
     * Called to retrieve per-instance state from an activity before being killed
     * so that the state can be restored in {@link #onCreate} or
     * {@link #onRestoreInstanceState} (the {@link Bundle} populated by this method
     * will be passed to both).
     *
     * <p>This method is called before an activity may be killed so that when it
     * comes back some time in the future it can restore its state.  For example,
     * if activity B is launched in front of activity A, and at some point activity
     * A is killed to reclaim resources, activity A will have a chance to save the
     * current state of its user interface via this method so that when the user
     * returns to activity A, the state of the user interface can be restored
     * via {@link #onCreate} or {@link #onRestoreInstanceState}.
     *
     * <p>Do not confuse this method with activity lifecycle callbacks such as
     * {@link #onPause}, which is always called when an activity is being placed
     * in the background or on its way to destruction, or {@link #onStop} which
     * is called before destruction.  One example of when {@link #onPause} and
     * {@link #onStop} is called and not this method is when a user navigates back
     * from activity B to activity A: there is no need to call {@link #onSaveInstanceState}
     * on B because that particular instance will never be restored, so the
     * system avoids calling it.  An example when {@link #onPause} is called and
     * not {@link #onSaveInstanceState} is when activity B is launched in front of activity A:
     * the system may avoid calling {@link #onSaveInstanceState} on activity A if it isn't
     * killed during the lifetime of B since the state of the user interface of
     * A will stay intact.
     *
     * <p>The default implementation takes care of most of the UI per-instance
     * state for you by calling {@link android.view.View#onSaveInstanceState()} on each
     * view in the hierarchy that has an id, and by saving the id of the currently
     * focused view (all of which is restored by the default implementation of
     * {@link #onRestoreInstanceState}).  If you override this method to save additional
     * information not captured by each individual view, you will likely want to
     * call through to the default implementation, otherwise be prepared to save
     * all of the state of each view yourself.
     *
     * <p>If called, this method will occur before {@link #onStop}.  There are
     * no guarantees about whether it will occur before or after {@link #onPause}.
     *
     * @param outState Bundle in which to place your saved state.
     *
     * @see #onCreate
     * @see #onRestoreInstanceState
     * @see #onPause
     */
    protected void onSaveInstanceState(Bundle outState) {
        outState.putBundle(WINDOW_HIERARCHY_TAG, mWindow.saveHierarchyState());
        Parcelable p = mFragments.saveAllState();
        if (p != null) {
            outState.putParcelable(FRAGMENTS_TAG, p);
        }
        getApplication().dispatchActivitySaveInstanceState(this, outState);
    }

PhoneWindow:

// This is the view in which the window contents are placed. It is either
    // mDecor itself, or a child of mDecor where the contents go.
    private ViewGroup mContentParent;

    ...

  /** {@inheritDoc} */
    @Override
    public Bundle saveHierarchyState() {
        Bundle outState = new Bundle();
        if (mContentParent == null) {
            return outState;
        }

        SparseArray<Parcelable> states = new SparseArray<Parcelable>();
        mContentParent.saveHierarchyState(states);
        outState.putSparseParcelableArray(VIEWS_TAG, states);

        // save the focused view id
        View focusedView = mContentParent.findFocus();
        if (focusedView != null) {
            if (focusedView.getId() != View.NO_ID) {
                outState.putInt(FOCUSED_ID_TAG, focusedView.getId());
            } else {
                if (false) {
                    Log.d(TAG, "couldn't save which view has focus because the focused view "
                            + focusedView + " has no id.");
                }
            }
        }

        // save the panels
        SparseArray<Parcelable> panelStates = new SparseArray<Parcelable>();
        savePanelState(panelStates);
        if (panelStates.size() > 0) {
            outState.putSparseParcelableArray(PANELS_TAG, panelStates);
        }

        if (mDecorContentParent != null) {
            SparseArray<Parcelable> actionBarStates = new SparseArray<Parcelable>();
            mDecorContentParent.saveToolbarHierarchyState(actionBarStates);
            outState.putSparseParcelableArray(ACTION_BAR_TAG, actionBarStates);
        }

        return outState;
    }

View:

/**
     * Store this view hierarchy's frozen state into the given container.
     *
     * @param container The SparseArray in which to save the view's state.
     *
     * @see #restoreHierarchyState(android.util.SparseArray)
     * @see #dispatchSaveInstanceState(android.util.SparseArray)
     * @see #onSaveInstanceState()
     */
    public void saveHierarchyState(SparseArray<Parcelable> container) {
        dispatchSaveInstanceState(container);
    }


 /**
     * Called by {@link #saveHierarchyState(android.util.SparseArray)} to store the state for
     * this view and its children. May be overridden to modify how freezing happens to a
     * view's children; for example, some views may want to not store state for their children.
     *
     * @param container The SparseArray in which to save the view's state.
     *
     * @see #dispatchRestoreInstanceState(android.util.SparseArray)
     * @see #saveHierarchyState(android.util.SparseArray)
     * @see #onSaveInstanceState()
     */
    protected void dispatchSaveInstanceState(SparseArray<Parcelable> container) {
        if (mID != NO_ID && (mViewFlags & SAVE_DISABLED_MASK) == 0) {
            mPrivateFlags &= ~PFLAG_SAVE_STATE_CALLED;
            Parcelable state = onSaveInstanceState();
            if ((mPrivateFlags & PFLAG_SAVE_STATE_CALLED) == 0) {
                throw new IllegalStateException(
                        "Derived class did not call super.onSaveInstanceState()");
            }
            if (state != null) {
                // Log.i("View", "Freezing #" + Integer.toHexString(mID)
                // + ": " + state);
                container.put(mID, state);
            }
        }
    }

ViewGroup:

/**
     * {@inheritDoc}
     */
    @Override
    protected void dispatchSaveInstanceState(SparseArray<Parcelable> container) {
        super.dispatchSaveInstanceState(container);
        final int count = mChildrenCount;
        final View[] children = mChildren;
        for (int i = 0; i < count; i++) {
            View c = children[i];
            if ((c.mViewFlags & PARENT_SAVE_DISABLED_MASK) != PARENT_SAVE_DISABLED) {
                c.dispatchSaveInstanceState(container);
            }
        }
    }