[Android] To implement state saving and restoration in the custom view.

TextView.java

// To implement state saving and restoration in the custom view...
// 
// You should implement the SavedState extend the BaseSavedState.
// You should be implemented to override the onSaveInstanceState and onRestoreInstanceState.
// TextView will be helpful.

// TextView 
public class TextView extends View implements ViewTreeObserver.OnPreDrawListener {

    /**
     * User interface state that is stored by TextView for implementing
     * {@link View#onSaveInstanceState}.
     */
    public static class SavedState extends BaseSavedState {
        int selStart;
        int selEnd;
        CharSequence text;
        boolean frozenWithFocus;
        CharSequence error;

        SavedState(Parcelable superState) {
            super(superState);
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeInt(selStart);
            out.writeInt(selEnd);
            out.writeInt(frozenWithFocus ? 1 : 0);
            TextUtils.writeToParcel(text, out, flags);

            if (error == null) {
                out.writeInt(0);
            } else {
                out.writeInt(1);
                TextUtils.writeToParcel(error, out, flags);
            }
        }

        @Override
        public String toString() {
            String str = "TextView.SavedState{"
                    + Integer.toHexString(System.identityHashCode(this))
                    + " start=" + selStart + " end=" + selEnd;
            if (text != null) {
                str += " text=" + text;
            }
            return str + "}";
        }

        @SuppressWarnings("hiding")
        public static final Parcelable.Creator<SavedState> CREATOR
                = new Parcelable.Creator<SavedState>() {
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };

        private SavedState(Parcel in) {
            super(in);
            selStart = in.readInt();
            selEnd = in.readInt();
            frozenWithFocus = (in.readInt() != 0);
            text = TextUtils.CHAR_SEQUENCE_CREATOR.createFromParcel(in);

            if (in.readInt() != 0) {
                error = TextUtils.CHAR_SEQUENCE_CREATOR.createFromParcel(in);
            }
        }
    }

    @Override
    public Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();

        // Save state if we are forced to
        boolean save = mFreezesText;
        int start = 0;
        int end = 0;

        if (mText != null) {
            start = getSelectionStart();
            end = getSelectionEnd();
            if (start >= 0 || end >= 0) {
                // Or save state if there is a selection
                save = true;
            }
        }

        if (save) {
            SavedState ss = new SavedState(superState);
            // XXX Should also save the current scroll position!
            ss.selStart = start;
            ss.selEnd = end;

            if (mText instanceof Spanned) {
                /*
                 * Calling setText() strips off any ChangeWatchers;
                 * strip them now to avoid leaking references.
                 * But do it to a copy so that if there are any
                 * further changes to the text of this view, it
                 * won't get into an inconsistent state.
                 */

                Spannable sp = new SpannableString(mText);

                for (ChangeWatcher cw : sp.getSpans(0, sp.length(), ChangeWatcher.class)) {
                    sp.removeSpan(cw);
                }

                removeMisspelledSpans(sp);
                sp.removeSpan(mSuggestionRangeSpan);

                ss.text = sp;
            } else {
                ss.text = mText.toString();
            }

            if (isFocused() && start >= 0 && end >= 0) {
                ss.frozenWithFocus = true;
            }

            ss.error = mError;

            return ss;
        }

        return superState;
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
        }

        SavedState ss = (SavedState)state;
        super.onRestoreInstanceState(ss.getSuperState());

        // XXX restore buffer type too, as well as lots of other stuff
        if (ss.text != null) {
            setText(ss.text);
        }

        if (ss.selStart >= 0 && ss.selEnd >= 0) {
            if (mText instanceof Spannable) {
                int len = mText.length();

                if (ss.selStart > len || ss.selEnd > len) {
                    String restored = "";

                    if (ss.text != null) {
                        restored = "(restored) ";
                    }

                    Log.e(LOG_TAG, "Saved cursor position " + ss.selStart +
                          "/" + ss.selEnd + " out of range for " + restored +
                          "text " + mText);
                } else {
                    Selection.setSelection((Spannable) mText, ss.selStart,
                                           ss.selEnd);

                    if (ss.frozenWithFocus) {
                        mFrozenWithFocus = true;
                    }
                }
            }
        }

        if (ss.error != null) {
            final CharSequence error = ss.error;
            // Display the error later, after the first layout pass
            post(new Runnable() {
                public void run() {
                    setError(error);
                }
            });
        }
    }

}