我正在开发一款绘图应用程序,onTouchEvents
是标准的,我想添加Undo()
函数以删除上次绘制的路径。
声明:
int thelastLineId=0;
private Bitmap bitmap; // drawing area for display or saving
private Canvas bitmapCanvas; // used to draw on bitmap
private Paint paintScreen; // use to draw bitmap onto screen
private Paint paintLine; // used to draw lines onto bitmap
private HashMap<Integer, Path> pathMap; // current Paths being drawn
private HashMap<Integer, Path> reservedpathMap; // for saving the paths being undone
private HashMap<Integer, Point> previousPointMap; // current Points
构造函数:
pathMap = new HashMap<Integer, Path>();
reservedpathMap = new HashMap <Integer,Path>(); // for storing path being undone
previousPointMap = new HashMap<Integer, Point>();
onDraw:
@Override
protected void onDraw(Canvas canvas)
{
canvas.drawBitmap(bitmap, 0, 0, paintScreen);
// for each path currently being drawn
for (Integer key : pathMap.keySet())
canvas.drawPath(pathMap.get(key), paintLine); // draw line
}
onTouchEvent:
@Override
public boolean onTouchEvent(MotionEvent event)
{
int action = event.getActionMasked(); // event type
int actionIndex = event.getActionIndex(); // pointer (i.e., finger)
if (action == MotionEvent.ACTION_DOWN)
{
touchStarted(event.getX(actionIndex), event.getY(actionIndex), event.getPointerId(actionIndex));
}
else if (action == MotionEvent.ACTION_UP)
{
touchEnded(event.getPointerId(actionIndex));
}
else
{
touchMoved(event);
}
invalidate();
return true;
}
touchStarted:
private void touchStarted(float x, float y, int lineID) // lineID represents how many fingers, 1 finger 1 line
{
Path path; // used to store the path for the given touch id
Point point; // used to store the last point in path
// if there is already a path for lineID
if (pathMap.containsKey(lineID))
{
path = pathMap.get(lineID); // get the Path
path.reset(); // reset the Path because a new touch has started
point = previousPointMap.get(lineID); // get Path's last point
}
else
{
path = new Path(); // create a new Path
pathMap.put(lineID, path); // add the Path to Map
point = new Point(); // create a new Point
previousPointMap.put(lineID, point); // add the Point to the Map
}
path.moveTo(x, y);
point.x = (int) x;
point.y = (int) y;
}
touchMoved:
private void touchMoved(MotionEvent event)
{
// for each of the pointers in the given MotionEvent
for (int i = 0; i < event.getPointerCount(); i++)
{
// get the pointer ID and pointer index
int pointerID = event.getPointerId(i);
int pointerIndex = event.findPointerIndex(pointerID);
// if there is a path associated with the pointer
if (pathMap.containsKey(pointerID))
{
float newX = event.getX(pointerIndex);
float newY = event.getY(pointerIndex);
// get the Path and previous Point associated with this pointer
Path path = pathMap.get(pointerID);
Point point = previousPointMap.get(pointerID);
float deltaX = Math.abs(newX - point.x);
float deltaY = Math.abs(newY - point.y);
if (deltaX >= TOUCH_TOLERANCE || deltaY >= TOUCH_TOLERANCE)
{
path.quadTo(point.x, point.y, ((newX + point.x)/2),((newY + point.y)/2));
point.x = (int) newX ;
point.y = (int) newY ;
}
}
}
touchEnded:
private void touchEnded(int lineID)
{
Path path = pathMap.get(lineID); // get the corresponding Path
bitmapCanvas.drawPath(path, paintLine);
path.reset();
}
撤销:
public void undo()
{
Toast.makeText(getContext(), "undo button pressed" + thelastLineId, Toast.LENGTH_SHORT).show();
Path path = pathMap.get(thelastLineId);
reservedpathMap.put(thelastLineId, path); // add the Path to reservedpathMap for later redo
pathMap.remove(thelastLineId);
invalidate();
}
问题:
我正在尝试使用上述代码实现UNDO方法:尝试从HashMap pathmap
中删除thelastLindId
键(并将其放入HashMap reservedpathMap
以供稍后 Redo 使用),这样当调用invalidate()
时,它将调用OnDraw()
并通过重新绘制来使其生效。
for (Integer key : pathMap.keySet())
canvas.drawPath(pathMap.get(key), paintLine);
然而,按下撤销按钮可以触发"已点击撤销"的提示,但最后画的线条未能消失。
请问有人能给我关于Undo()和Redo()的提示吗?非常感谢!