代码来自：https://issuetracker.google.com/issues/36913735#c123
package fi.iki.asb.android.logo;
/*
* THIS CLASS IS PROVIDED TO THE PUBLIC DOMAIN FOR FREE WITHOUT ANY
* RESTRICTIONS OR ANY WARRANTY.
*/
import java.util.LinkedList;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.text.Editable;
import android.text.Selection;
import android.text.TextWatcher;
import android.text.style.UnderlineSpan;
import android.widget.TextView;
/**
* A generic undo/redo implementation for TextViews.
*/
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) {
}
}
}
使用
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button redoBtn = (Button) findViewById(R.id.redo);
Button undoBtn = (Button) findViewById(R.id.undo);
EditText editText = (EditText) findViewById(R.id.edittext);
// pass edittext object to TextViewUndoRedo class
TextViewUndoRedo helper = new TextViewUndoRedo(edittext);
// call the method from TextViewUndoRedo class
redoBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
helper.redo(); // perform redo
}
});
undoBtn.setOnClickLisener(new View.OnClickListener() {
@Override
public void onClick(View v) {
helper.undo(); // perform undo
}
});
}
}
代码下载：https://gist.github.com/zeleven/0cfa738c1e8b65b23ff7df1fc30c9f7e
