我对android中的canvas感到有些困惑，并且想知道是否有人可以为我澄清一些事情。
我目前在View类中有这个代码：
class HomerView extends View { // the custom View for drawing on
// set up Bitmap, canvas, path and paint
private Bitmap myBitmap; // the initial image we turn into our canvas
private Canvas myCanvas; // the canvas we are drawing on
private Rect myRect; // the mathematical path of the lines we draw
private Paint myBitmapPaint; // the paint we use to draw the bitmap
// get the width of the entire tablet screen
private int screenWidth = getContext().getResources()
.getDisplayMetrics().widthPixels;
// get the height of the entire tablet screen
private int screenHeight = getContext().getResources()
.getDisplayMetrics().heightPixels;
private int mX, mY, iX, iY; // current x,y and initial x,y
private static final float TOUCH_TOLERANCE = 4;
private static final int INVALID_POINTER_ID = -1;
private float mPosX;
private float mPosY;
private BitmapDrawable mImage;
private float mLastTouchX;
private float mLastTouchY;
private int mActivePointerId = INVALID_POINTER_ID;
private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;
public HomerView(Context context) { // constructor of HomerView
super(context);
myBitmap = Bitmap.createBitmap(screenWidth, screenHeight,
Bitmap.Config.ARGB_8888); // set our drawable space - the bitmap which becomes the canvas we draw on
myCanvas = new Canvas(myBitmap); // set our canvas to our bitmap which we just set up
myRect = new Rect(); // make a new rect
myBitmapPaint = new Paint(Paint.DITHER_FLAG); // set dither to ON in our saved drawing - gives better color interaction
setHorizontalScrollBarEnabled(true);
setVerticalScrollBarEnabled(true);
TypedArray a = context.obtainStyledAttributes(R.styleable.View);
initializeScrollbars(a);
a.recycle();
computeVerticalScrollRange();
computeHorizontalScrollRange();
mImage = new BitmapDrawable(getResources(), myBitmap);
mScaleDetector = new ScaleGestureDetector(context,
new ScaleListener());
}
public HomerView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mScaleDetector = new ScaleGestureDetector(context,
new ScaleListener());
}
public HomerView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
protected void onDraw(Canvas canvas) { // method used when we want to draw something to our canvas
super.onDraw(canvas);
if (addObjectMode == true) {
canvas.drawColor(Color.TRANSPARENT); // sets canvas colour
canvas.drawBitmap(myBitmap, 0, 0, myBitmapPaint); // save the canvas to bitmap - the numbers are the x, y coords we are drawing from
canvas.drawRect(myRect, myPaint); // draw the rectangle that the user has drawn using the paint we set up
} else if (moveMode == true) {
canvas.save();
System.out.println("X: " + mPosX + " Y: " + mPosY);
canvas.translate(mPosX, mPosY);
canvas.scale(mScaleFactor, mScaleFactor);
mImage.draw(canvas);
canvas.restore();
}
根据我的理解，这是两种不同的绘制到屏幕的方法的合并。我的理解是我有myBitmap（这是用户绘图的用法），这适用于“addObjectMode”。但是，“moveMode”是指我希望用户能够在他们绘制的房屋计划周围捏缩放滚动等。
目前，我可以很好地绘制对象，但是当我按下按钮启用moveMode时，当我触摸或手势时，绘图会消失。我知道这可能是因为onDraw()中的代码;但帆布对我来说仍然有点神秘。
最终，我将需要一个基本的撤消/重做功能，并保存稍后要打开的canvas/bitmap。任何人都可以提供任何建议或链接到任何全面的画布教程吗？
编辑：包含我的onTouchEvent方法可能也很有用 -
public boolean onTouchEvent(MotionEvent event) { // on any touch event
if (addObjectMode == true) {
float x = event.getX(); // get current X
float y = event.getY(); // get current Y
switch (event.getAction()) { // what action is the user performing?
case MotionEvent.ACTION_DOWN: // if user is touching down
touch_Start(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE: // if user is moving finger while touched down
touch_Move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP: // if user has released finger
touch_Up();
invalidate();
break;
}
return true;
} else if (moveMode == true) {
mScaleDetector.onTouchEvent(event);
final int action = event.getAction();
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
final float x = event.getX();
final float y = event.getY();
mLastTouchX = x;
mLastTouchY = y;
mActivePointerId = event.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE: {
final int pointerIndex = event
.findPointerIndex(mActivePointerId);
final float x = event.getX(pointerIndex);
final float y = event.getY(pointerIndex);
// Only move if the ScaleGestureDetector isn't processing a gesture.
if (!mScaleDetector.isInProgress()) {
final float dx = x - mLastTouchX;
final float dy = y - mLastTouchY;
mPosX += dx;
mPosY += dy;
invalidate();
}
mLastTouchX = x;
mLastTouchY = y;
break;
}
case MotionEvent.ACTION_UP: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_CANCEL: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_UP: {
final int pointerIndex = (event.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = event.getPointerId(pointerIndex);
if (pointerId == mActivePointerId) {
// This was our active pointer going up. Choose a new
// active pointer and adjust accordingly.
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastTouchX = event.getX(newPointerIndex);
mLastTouchY = event.getY(newPointerIndex);
mActivePointerId = event.getPointerId(newPointerIndex);
}
break;
}
}
return true;
} else {
return false;
}
}
答案 0 :(得分：1)
在您的示例中，当您在moveMode中时，您不会在最终画布上绘制任何内容。
即使您正在对已绘制的内容应用转换，请注意两次调用onDraw（）之间的画布是清晰的，因此您可以再次绘制它。
我不熟悉撤消重做功能，但您应该能够在给定点存储画布位图的副本以便以后恢复
请注意，存储大量位图对于移动环境来说可能非常繁重，因此您必须限制撤消堆栈大小。
答案 1 :(得分：0)
删除draw方法的if else if条件，对于undo功能，创建位图的arraylist，并在每次用户执行某些操作时保存位图，然后在undo上将位图替换为previous并使视图无效
答案 2 :(得分：0)
为了实现Undo \ Redo，您需要维护路径列表...并且必须相应地将这些路径存储在路径列表中。我已经在下面附上了我的代码，看看它然后你会得到一些关于撤销重做功能的明确想法。
public static LinkedList<Path> rrPathList=new LinkedList<Path>();
public static LinkedList<Path> mPathList=new LinkedList<Path>();
protected void onDraw(Canvas canvas) {
for( i = 0; i < mPathList.size() && i < sPaint.size(); i++ )
{
canvas.drawPath(mPathList.get(i),sPaint.get(i));
}
}
// In your touch up method store the paths into mPathList
private void touch_up() {
mCanvas.drawPath(mPath, mPaint);
mPathList.add(mPath);
}
// Undo function
public void undo()
{
try
{
if(mPathList.size()>0)
{
rPathList.add(mPathList.getLast());
mPathList.removeLast();
invalidate();
}
}catch(ArrayIndexOutOfBoundsException arr)
{
//Print error;
}
}
// Redo function
public void redo()
{
try
{
if(rPathList.size()>0)
{
mPathList.add(rPathList.getLast());
rPathList.removeLast();
invalidate();
}
}catch(ArrayIndexOutOfBoundsException arr)
{
//Handle error
}
}
注意：请不要忘记调用“invalidate（）”。 调用invalidate results“调用画布并重绘mPathList对象” 试试这个。我正在使用这段代码...... 谢谢!!!