如何在 canvas 上执行 Undo/Redo 操作。而且我的代码很糟糕，我没有执行这两个操作。在主类中，由于这个原因正在执行绘画，我没有执行撤消重做操作。
public class MainActivity extends Activity implements OnClickListener{
MyView mView;
private Path mPath;
Button btnUndo,btnRedo;
FrameLayout frmLayout;
private Paint mPaint;
private MaskFilter mEmboss;
Bitmap mBitmap;
int bckcolor=0xffffffff;
final Context context = this;
ArrayList<Path> paths = new ArrayList<Path>();
ArrayList<Path> undonePaths = new ArrayList<Path>();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mView = new MyView(this);
setContentView(R.layout.activity_main);
btnUndo=(Button)findViewById(R.id.Undo);
btnRedo=(Button)findViewById(R.id.Redo);
btnUndo.setOnClickListener(this);
btnRedo.setOnClickListener(this);
frmLayout=(FrameLayout)findViewById(R.id.frameLayout);
frmLayout.addView(mView,LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
mPaint = new Paint();
mPath=new Path();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(0xFF000000);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(5);
new Canvas();
paths.add(mPath);
mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },0.4f, 6, 3.5f);
new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
switch (v.getId()) {
case R.id.Undo:
if (paths.size()>0)
{
undonePaths.add(paths.remove(paths.size()-1));
mView.invalidate();
Toast.makeText(getApplicationContext(), "Undo", 1000).show();
}
mView.undo();
break;
case R.id.Redo:
mView.redo();
break;
default:
break;
}
}
public class MyView extends View {
private float posX = 105;
private float posY = 105;
Mode mode;
private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
private Paint mBitmapPaint;
ArrayList<Path> paths = new ArrayList<Path>();
ArrayList<Path> undonePaths = new ArrayList<Path>();
BlurMaskFilter blurMaskFilter = new BlurMaskFilter(10, BlurMaskFilter.Blur.OUTER);
int screenWidth;
int screenHeight;
/**
*/
public MyView(Context c)
{
super(c);
mBitmap=BitmapFactory.decodeResource(getResources(), R.drawable.e);
mBitmap = Bitmap.createBitmap(800, 800, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
mCanvas.drawColor(0xFFFFFFFF);
paths.add(mPath);
}
public void redo() {
// TODO Auto-generated method stub
if (undonePaths.size()>0)
{
paths.add(undonePaths.remove(undonePaths.size()-1));
invalidate();
}
else
{
}
}
public void undo() {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(), "Hello", 1000).show();
if (paths.size()>0)
{
undonePaths.add(paths.remove(paths.size()-1));
mView.invalidate();
Toast.makeText(getApplicationContext(), "Undo", 1000).show();
}
else
{
Toast.makeText(getApplicationContext(), "Not", 1000).show();
}
}
@Override protected void onSizeChanged(int w, int h, int oldw, int oldh)
{
super.onSizeChanged(w, h, oldw, oldh);
}
/**
*/
@Override protected void onDraw(Canvas canvas)
{
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
for(Path p:paths)
{
canvas.drawPath(p, mPaint);
}
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
mX = x;
mY = y;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
mCanvas.drawPath(mPath, mPaint);
paths.add(mPath);
mPath.reset();
}
@Override public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
touch_start(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
public void drawImage (int resourceId)
{
Bitmap _scratch = BitmapFactory.decodeResource(getResources(), resourceId);
mCanvas.drawBitmap(_scratch, 0, 0, null);
}
}
}