我需要在我的应用中添加以下功能
我必须将位图显示到画布中
然后用户可以放大和缩小位图到画布中
如何使其成为可能？ 我只需要在Canvas中而不在ImageView中需要它
所有答案对我都没有太大帮助。所以我想更新我的问题
基本上我需要一个简单的2按钮和一个画布...
在第一个按钮上单击时，画布上的图像可以旋转/放大和缩小，在单击第二个按钮时，它必须显示由用户创建的放大或缩小的图像，此后，用户必须不能缩放或缩小该画布
如果您在画布中放大和缩小位图，请使用下面的代码作为代码
在您的活动中添加您的代码
MyView myView = new MyView(this);
setContentView(myView);
并且在您的视图下方。
public class MyView extends View {
private Drawable image;
private ScaleGestureDetector scaleDetector;
private float scaleFactor = 1.f;
public MyView(Context context) {
super(context);
init(context);
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
public MyView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context);
}
private void init(Context ctx) {
image = getResources().getDrawable(R.drawable.ic_launcher);
image.setBounds(0, 0, image.getIntrinsicWidth(),
image.getIntrinsicHeight());
scaleDetector = new ScaleGestureDetector(ctx, new ScaleListener());
}
@Override
protected void onDraw(Canvas canvas) {
canvas.save();
canvas.scale(scaleFactor, scaleFactor);
image.draw(canvas);
canvas.restore();
};
@Override
public boolean onTouchEvent(MotionEvent ev) {
scaleDetector.onTouchEvent(ev);
return true;
}
private class ScaleListener extends
ScaleGestureDetector.SimpleOnScaleGestureListener {
@Override
public boolean onScale(ScaleGestureDetector detector) {
scaleFactor *= detector.getScaleFactor();
scaleFactor = Math.max(0.1f, Math.min(scaleFactor, 10.0f));
invalidate();
return true;
}
}
}
您可以使用此自定义视图类，它提供拖动以及缩放效果。我不是此类的原始作者，我从此tutorial中复制了它。如果您想逐步了解如何实现此效果，可以通过tutorial pages。
public class ZoomView extends View {
//These two constants specify the minimum and maximum zoom
private static float MIN_ZOOM = 1f;
private static float MAX_ZOOM = 5f;
private float scaleFactor = 1.f;
private ScaleGestureDetector detector;
//These constants specify the mode that we're in
private static int NONE = 0;
private static int DRAG = 1;
private static int ZOOM = 2;
private int mode;
//These two variables keep track of the X and Y coordinate of the finger when it first
//touches the screen
private float startX = 0f;
private float startY = 0f;
//These two variables keep track of the amount we need to translate the canvas along the X
//and the Y coordinate
private float translateX = 0f;
private float translateY = 0f;
//These two variables keep track of the amount we translated the X and Y coordinates, the last time we
//panned.
private float previousTranslateX = 0f;
private float previousTranslateY = 0f;
public ZoomView(Context context) {
super(context);
detector = new ScaleGestureDetector(getContext(), new ScaleListener());
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
mode = DRAG;
//We assign the current X and Y coordinate of the finger to startX and startY minus the previously translated
//amount for each coordinates This works even when we are translating the first time because the initial
//values for these two variables is zero.
startX = event.getX() - previousTranslateX;
startY = event.getY() - previousTranslateY;
break;
case MotionEvent.ACTION_MOVE:
translateX = event.getX() - startX;
translateY = event.getY() - startY;
//We cannot use startX and startY directly because we have adjusted their values using the previous translation values.
//This is why we need to add those values to startX and startY so that we can get the actual coordinates of the finger.
double distance = Math.sqrt(Math.pow(event.getX() - (startX + previousTranslateX), 2) +
Math.pow(event.getY() - (startY + previousTranslateY), 2)
);
if(distance > 0) {
dragged = true;
}
break;
case MotionEvent.ACTION_POINTER_DOWN:
mode = ZOOM;
break;
case MotionEvent.ACTION_UP:
mode = NONE;
dragged = false;
//All fingers went up, so let's save the value of translateX and translateY into previousTranslateX and
//previousTranslate
previousTranslateX = translateX;
previousTranslateY = translateY;
break;
case MotionEvent.ACTION_POINTER_UP:
mode = DRAG;
//This is not strictly necessary; we save the value of translateX and translateY into previousTranslateX
//and previousTranslateY when the second finger goes up
previousTranslateX = translateX;
previousTranslateY = translateY;
break;
}
detector.onTouchEvent(event);
//We redraw the canvas only in the following cases:
//
// o The mode is ZOOM
// OR
// o The mode is DRAG and the scale factor is not equal to 1 (meaning we have zoomed) and dragged is
// set to true (meaning the finger has actually moved)
if ((mode == DRAG && scaleFactor != 1f && dragged) || mode == ZOOM) {
invalidate();
}
return true;
}
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save();
//We're going to scale the X and Y coordinates by the same amount
canvas.scale(scaleFactor, scaleFactor);
//If translateX times -1 is lesser than zero, let's set it to zero. This takes care of the left bound
if((translateX * -1) < 0) {
translateX = 0;
}
//This is where we take care of the right bound. We compare translateX times -1 to (scaleFactor - 1) * displayWidth.
//If translateX is greater than that value, then we know that we've gone over the bound. So we set the value of
//translateX to (1 - scaleFactor) times the display width. Notice that the terms are interchanged; it's the same
//as doing -1 * (scaleFactor - 1) * displayWidth
else if((translateX * -1) > (scaleFactor - 1) * displayWidth) {
translateX = (1 - scaleFactor) * displayWidth;
}
if(translateY * -1 < 0) {
translateY = 0;
}
//We do the exact same thing for the bottom bound, except in this case we use the height of the display
else if((translateY * -1) > (scaleFactor - 1) * displayHeight) {
translateY = (1 - scaleFactor) * displayHeight;
}
//We need to divide by the scale factor here, otherwise we end up with excessive panning based on our zoom level
//because the translation amount also gets scaled according to how much we've zoomed into the canvas.
canvas.translate(translateX / scaleFactor, translateY / scaleFactor);
/* The rest of your canvas-drawing code */
canvas.restore();
}
private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
@Override
public boolean onScale(ScaleGestureDetector detector) {
scaleFactor *= detector.getScaleFactor();
scaleFactor = Math.max(MIN_ZOOM, Math.min(scaleFactor, MAX_ZOOM));
return true;
}
}
}
您可以检查条件if (scaleFactor == 1.f)，然后将所有变量设置为默认值，并在方法postInvalidate()中调用onTouchEvent。
例如：
@Override
public boolean onTouchEvent(MotionEvent ev) {
scaleDetector.onTouchEvent(ev);
if (scaleFactor <= 1.f){
//set all variables of zooming and scrolling to default
scaleFactor = 1.f;
postinvalidate();
}
return true;
}