我正在开发一个绘图应用程序，但面临一些撤消问题。编码如下：
public class DoodleView extends View
{
Context context_new;
private static final float TOUCH_TOLERANCE = 5;
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 Path mPath;
private ArrayList<Path> paths = new ArrayList<Path>();
private ArrayList<Path> undonePaths = new ArrayList<Path>();
private float mX, mY;
// DoodleView constructor initializes the DoodleView
public DoodleView(Context context, AttributeSet attrs)
{
super(context, attrs); // pass context to View's constructor
this.context_new=context;
paintScreen = new Paint(); // used to display bitmap onto screen
// set the initial display settings for the painted line
paintLine = new Paint();
paintLine.setAntiAlias(true); // smooth edges of drawn line
paintLine.setColor(Color.BLACK); // default color is black
paintLine.setStyle(Paint.Style.STROKE); // solid line
mPath = new Path();
paths.add(mPath);
} // end DoodleView constructor
OnSizeChange:
@Override
public void onSizeChanged(int w, int h, int oldW, int oldH)
{
super.onSizeChanged(w, h, oldW, oldH);
DoodlzViewWidth = w;
DoodlzViewHeight = h;
bitmap = Bitmap.createBitmap(getWidth(), DoodlzViewHeight, Bitmap.Config.ARGB_8888);
bitmapCanvas = new Canvas(bitmap);
bitmap.eraseColor(Color.WHITE); // erase the BitMap with white
}
onDraw:
@Override
protected void onDraw(Canvas canvas)
{
canvas.drawBitmap(bitmap, 0, 0, paintScreen);
// for each path currently being drawn
for (Path p : paths){canvas.drawPath(p, paintLine);}
}
onTouchEvent：
@Override
public boolean onTouchEvent(MotionEvent event)
{
float x = event.getX();
float y = event.getY();
switch (event.getAction())
{
case MotionEvent.ACTION_DOWN:
touchStarted(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
touchMoved(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touchEnded();
invalidate();
break;
}
return true;
}
touchStarted:
private void touchStarted(float x, float y)
{
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
touchMoved:
private void touchMoved(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;
}
}
触摸结束：
private void touchEnded()
{
mPath.lineTo(mX, mY);
bitmapCanvas.drawPath(mPath, paintLine);
mPath = new Path();
paths.add(mPath);
Toast.makeText(getContext(), "touchEnded" + paths.size(), Toast.LENGTH_SHORT).show();
}
撤消：
public void onClickUndo()
{
Toast.makeText(getContext(), "before undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();
if (paths.size()>0)
{
undonePaths.add(paths.remove(paths.size()-1));
Toast.makeText(getContext(), "after undo button pressed " + paths.size(), Toast.LENGTH_SHORT).show();
Log.i("UNDOING", "PREPARE INVALIDATE");
invalidate();
Log.i("UNDOING", "FINISH INVALIDATE");
}
else Toast.makeText(getContext(), "nothing to undo" + paths.size(), Toast.LENGTH_SHORT).show();
}
问题：
以上内容来源于在线搜索的其他示例。不知道为什么在实现touchStarted时需要设置path.reset（）？
Q1.当我按下撤销按钮时，它将正确显示按下的toast撤销按钮，并报告path.size()为0，因此之前绘制的直线未删除。我真的不知道为什么是0？？它是否已经添加到路径数组中？如何修改代码？
**代码修改后采纳android开发者的建议！谢谢它现在正确地显示了path.size（）。很抱歉错过了！*但上一条线仍然无法删除=（
Q2.当手指在屏幕上移动并立即显示线条时，应用程序运行正常，当我按下撤消按钮时，除了上面的前一行没有删除外，按下按钮后进一步绘制到屏幕上的线条在手指抬起之前不会显示出来。
对Q2的回答：将以下2行从touchEnded()移动到touchStarted()
mPath = new Path();
paths.add(mPath);
private void touchStarted(float x, float y)
{
mPath.reset();
mPath = new Path();
paths.add(mPath);
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touchEnded()
{
mPath.lineTo(mX, mY);
bitmapCanvas.drawPath(mPath, paintLine);// commit the path to our offscreen
Toast.makeText(getContext(), "touchEnded" + paths.size(), Toast.LENGTH_SHORT).show();
}
谢谢！！！
已更新并工作：
- 移除了Paint paintScreen
-
在onDraw中不要放置
canvas.drawBitmap(bitmap, 0, 0, paintScreen);或canvas.drawBitmap(bitmap, 0, 0, paintLine);private Bitmap bitmap; // drawing area for display or saving private Canvas bitmapCanvas; // used to draw on bitmap private Paint paintLine; // used to draw lines onto bitmap private Path mPath; private ArrayList<Path> paths = new ArrayList<Path>(); private ArrayList<Path> undonePaths = new ArrayList<Path>(); private float mX, mY; private static final float TOUCH_TOLERANCE = 4; // DoodleView constructor initializes the DoodleView public DoodleView(Context context, AttributeSet attrs) { super(context, attrs); // pass context to View's constructor this.context_new=context; setFocusable(true); setFocusableInTouchMode(true); // set the initial display settings for the painted line paintLine = new Paint(); paintLine.setAntiAlias(true); // smooth edges of drawn line paintLine.setDither(true); paintLine.setColor(Color.BLACK); // default color is black paintLine.setStyle(Paint.Style.STROKE); // solid line paintLine.setStrokeJoin(Paint.Join.ROUND); paintLine.setStrokeWidth(5); // set the default line width paintLine.setStrokeCap(Paint.Cap.ROUND); // rounded line ends bitmapCanvas = new Canvas(); mPath = new Path(); } // end DoodleView constructor // Method onSizeChanged creates BitMap and Canvas after app displays @Override public void onSizeChanged(int w, int h, int oldW, int oldH) { super.onSizeChanged(w, h, oldW, oldH); DoodlzViewWidth = w; DoodlzViewHeight = h; } @Override protected void onDraw(Canvas canvas) { for (Path p : paths){canvas.drawPath(p, paintLine);} canvas.drawPath(mPath, paintLine); Log.i("OnDRAWING", "REACH ON DRAW"); }//START TOUCH：处理触摸事件@覆盖
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; } private void touch_start(float x, float y) { undonePaths.clear(); 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); bitmapCanvas.drawPath(mPath, paintLine);// commit the path to our offscreen paths.add(mPath); mPath = new Path(); } public void onClickUndo() { if (paths.size()>0) { undonePaths.add(paths.remove(paths.size()-1)); invalidate(); } else Toast.makeText(getContext(), "nothing more to undo", Toast.LENGTH_SHORT).show(); }