java - 撤消所有文本时如何禁用按钮？

Question

我正在使用一个简单的库来进行撤消和重做并且效果很好，但唯一的问题是当我在获取所有已删除文本的末尾不断单击撤消按钮时，它会清除我的所有文本。我不想清除我的所有文本，而是在通过单击撤消按钮获取所有文本后我希望撤消按钮禁用。

这是我正在使用的用于撤消和重做的 java

 public class TextViewUndoRedo {

    /**
     * Is undo/redo being performed? This member signals if an undo/redo
     * operation is currently being performed. Changes in the text during
     * undo/redo are not recorded because it would mess up the undo history.
     */
    private boolean mIsUndoOrRedo = false;

    /**
     * The edit history.
     */
    private EditHistory mEditHistory;

    /**
     * The change listener.
     */
    private EditTextChangeListener mChangeListener;

    /**
     * The edit text.
     */
    private TextView mTextView;

    // =================================================================== //

    /**
     * Create a new TextViewUndoRedo and attach it to the specified TextView.
     *
     * @param textView
     *            The text view for which the undo/redo is implemented.
     */
    public TextViewUndoRedo(TextView textView) {
        mTextView = textView;
        mEditHistory = new EditHistory();
        mChangeListener = new EditTextChangeListener();
        mTextView.addTextChangedListener(mChangeListener);
    }

    // =================================================================== //

    /**
     * Disconnect this undo/redo from the text view.
     */
    public void disconnect() {
        mTextView.removeTextChangedListener(mChangeListener);
    }

    /**
     * Set the maximum history size. If size is negative, then history size is
     * only limited by the device memory.
     */
    public void setMaxHistorySize(int maxHistorySize) {
        mEditHistory.setMaxHistorySize(maxHistorySize);
    }

    /**
     * Clear history.
     */
   /* public void clearHistory() {
        mEditHistory.clear();
    }*/

    /**
     * Can undo be performed?
     */
    public boolean getCanUndo() {
        return (mEditHistory.mmPosition > 0);
    }

    /**
     * Perform undo.
     */
    public void undo() {
        EditItem edit = mEditHistory.getPrevious();
        if (edit == null) {
            return;
        }

        Editable text = mTextView.getEditableText();
        int start = edit.mmStart;
        int end = start + (edit.mmAfter != null ? edit.mmAfter.length() : 0);

        mIsUndoOrRedo = true;
        text.replace(start, end, edit.mmBefore);
        mIsUndoOrRedo = false;

        // This will get rid of underlines inserted when editor tries to come
        // up with a suggestion.
        for (Object o : text.getSpans(0, text.length(), UnderlineSpan.class)) {
            text.removeSpan(o);
        }

        Selection.setSelection(text, edit.mmBefore == null ? start
                : (start + edit.mmBefore.length()));
    }

    /**
     * Can redo be performed?
     */
    public boolean getCanRedo() {
        return (mEditHistory.mmPosition < mEditHistory.mmHistory.size());
    }

    /**
     * Perform redo.
     */
    public void redo() {
        EditItem edit = mEditHistory.getNext();
        if (edit == null) {
            return;
        }

        Editable text = mTextView.getEditableText();
        int start = edit.mmStart;
        int end = start + (edit.mmBefore != null ? edit.mmBefore.length() : 0);

        mIsUndoOrRedo = true;
        text.replace(start, end, edit.mmAfter);
        mIsUndoOrRedo = false;

        // This will get rid of underlines inserted when editor tries to come
        // up with a suggestion.
        for (Object o : text.getSpans(0, text.length(), UnderlineSpan.class)) {
            text.removeSpan(o);
        }

        Selection.setSelection(text, edit.mmAfter == null ? start
                : (start + edit.mmAfter.length()));
    }

    /**
     * Store preferences.
     */
    public void storePersistentState(Editor editor, String prefix) {
        // Store hash code of text in the editor so that we can check if the
        // editor contents has changed.
        editor.putString(prefix + ".hash",
                String.valueOf(mTextView.getText().toString().hashCode()));
        editor.putInt(prefix + ".maxSize", mEditHistory.mmMaxHistorySize);
        editor.putInt(prefix + ".position", mEditHistory.mmPosition);
        editor.putInt(prefix + ".size", mEditHistory.mmHistory.size());

        int i = 0;
        for (EditItem ei : mEditHistory.mmHistory) {
            String pre = prefix + "." + i;

            editor.putInt(pre + ".start", ei.mmStart);
            editor.putString(pre + ".before", ei.mmBefore.toString());
            editor.putString(pre + ".after", ei.mmAfter.toString());

            i++;
        }
    }

    /**
     * Restore preferences.
     *
     * @param prefix
     *            The preference key prefix used when state was stored.
     * @return did restore succeed? If this is false, the undo history will be
     *         empty.
     */
    public boolean restorePersistentState(SharedPreferences sp, String prefix)
            throws IllegalStateException {

        boolean ok = doRestorePersistentState(sp, prefix);
        if (!ok) {
            mEditHistory.clear();
        }

        return ok;
    }

    private boolean doRestorePersistentState(SharedPreferences sp, String prefix) {

        String hash = sp.getString(prefix + ".hash", null);
        if (hash == null) {
            // No state to be restored.
            return true;
        }

        if (Integer.valueOf(hash) != mTextView.getText().toString().hashCode()) {
            return false;
        }

        mEditHistory.clear();
        mEditHistory.mmMaxHistorySize = sp.getInt(prefix + ".maxSize", -1);

        int count = sp.getInt(prefix + ".size", -1);
        if (count == -1) {
            return false;
        }

        for (int i = 0; i < count; i++) {
            String pre = prefix + "." + i;

            int start = sp.getInt(pre + ".start", -1);
            String before = sp.getString(pre + ".before", null);
            String after = sp.getString(pre + ".after", null);

            if (start == -1 || before == null || after == null) {
                return false;
            }
            mEditHistory.add(new EditItem(start, before, after));
        }

        mEditHistory.mmPosition = sp.getInt(prefix + ".position", -1);
        if (mEditHistory.mmPosition == -1) {
            return false;
        }

        return true;
    }

    // =================================================================== //

    /**
     * Keeps track of all the edit history of a text.
     */
    private final class EditHistory {

        /**
         * The position from which an EditItem will be retrieved when getNext()
         * is called. If getPrevious() has not been called, this has the same
         * value as mmHistory.size().
         */
        private int mmPosition = 0;

        /**
         * Maximum undo history size.
         */
        private int mmMaxHistorySize = -1;

        /**
         * The list of edits in chronological order.
         */
        private final LinkedList<EditItem> mmHistory = new LinkedList<EditItem>();

        /**
         * Clear history.
         */
        private void clear() {
            mmPosition = 0;
            mmHistory.clear();
        }

        /**
         * Adds a new edit operation to the history at the current position. If
         * executed after a call to getPrevious() removes all the future history
         * (elements with positions >= current history position).
         */
        private void add(EditItem item) {
            while (mmHistory.size() > mmPosition) {
                mmHistory.removeLast();
            }
            mmHistory.add(item);
            mmPosition++;

            if (mmMaxHistorySize >= 0) {
                trimHistory();
            }
        }

        /**
         * Set the maximum history size. If size is negative, then history size
         * is only limited by the device memory.
         */
        private void setMaxHistorySize(int maxHistorySize) {
            mmMaxHistorySize = maxHistorySize;
            if (mmMaxHistorySize >= 0) {
                trimHistory();
            }
        }

        /**
         * Trim history when it exceeds max history size.
         */
        private void trimHistory() {
            while (mmHistory.size() > mmMaxHistorySize) {
                mmHistory.removeFirst();
                mmPosition--;
            }

            if (mmPosition < 0) {
                mmPosition = 0;
            }
        }

        /**
         * Traverses the history backward by one position, returns and item at
         * that position.
         */
        private EditItem getPrevious() {
            if (mmPosition == 0) {
                return null;
            }
            mmPosition--;
            return mmHistory.get(mmPosition);
        }

        /**
         * Traverses the history forward by one position, returns and item at
         * that position.
         */
        private EditItem getNext() {
            if (mmPosition >= mmHistory.size()) {
                return null;
            }

            EditItem item = mmHistory.get(mmPosition);
            mmPosition++;
            return item;
        }
    }

    /**
     * Represents the changes performed by a single edit operation.
     */
    private final class EditItem {
        private final int mmStart;
        private final CharSequence mmBefore;
        private final CharSequence mmAfter;

        /**
         * Constructs EditItem of a modification that was applied at position
         * start and replaced CharSequence before with CharSequence after.
         */
        public EditItem(int start, CharSequence before, CharSequence after) {
            mmStart = start;
            mmBefore = before;
            mmAfter = after;
        }
    }

    /**
     * Class that listens to changes in the text.
     */
    private final class EditTextChangeListener implements TextWatcher {

        /**
         * The text that will be removed by the change event.
         */
        private CharSequence mBeforeChange;

        /**
         * The text that was inserted by the change event.
         */
        private CharSequence mAfterChange;

        public void beforeTextChanged(CharSequence s, int start, int count,
                                      int after) {
            if (mIsUndoOrRedo) {
                return;
            }

            mBeforeChange = s.subSequence(start, start + count);
        }

        public void onTextChanged(CharSequence s, int start, int before,
                                  int count) {
            if (mIsUndoOrRedo) {
                return;
            }

            mAfterChange = s.subSequence(start, start + count);
            mEditHistory.add(new EditItem(start, mBeforeChange, mAfterChange));
        }

        public void afterTextChanged(Editable s) {
        }
    }
}

还有我的按钮和 Activity

switch (v.getId()) {
        case R.id.undo:
            mTextViewUndoRedo.undo();
            break;
        case R.id.redo:
            mTextViewUndoRedo.redo();
            break;

Answer 1

你的撤消工作应该在最后阶段之前返回。

public boolean getCanUndo() {
    return (mEditHistory.mmPosition > 1); 
 }