问题
i'm trying to implement pinch zoom and panning options for canvas i'm using the code (slightly modified, i've added DisplayMetrics to automatically set devices screen size) from this webpage http://vivin.net/2011/12/04/implementing-pinch-zoom-and-pandrag-in-an-android-view-on-the-canvas/8/
As a result i have just an image opening in app(not whole though, just a fragment cause its bigger than screen size), image is not zooming and not panning, its just rotating when i rotate the phone. I used another code before, simplier, just for the zoom and it was working. I was sitting in front of this a lot of time and i have no clue what's wrong. It looks like its all right but it doesn't work. Maybe you guys know what am i doing wrong.
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
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;
DisplayMetrics displayMetrics = this.getResources().getDisplayMetrics();
int displayWidth = displayMetrics.widthPixels;
int displayHeight = displayMetrics.heightPixels;
//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;
public boolean dragged = true;
//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) {
final int action = event.getAction();
switch (action & 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;
}
Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.pozegnanie);
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save();
canvas.drawBitmap(bmp, 0, 0, null);
canvas.scale(this.scaleFactor, this.scaleFactor, this.detector.getFocusX(), this.detector.getFocusY());
canvas.translate(translateX / scaleFactor, translateY / 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.
/* 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;
}
}
}
And this is my activity class:
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
public class zoom extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ZoomView zoom = new ZoomView(this);
setContentView(zoom);
}
来源：https://stackoverflow.com/questions/25941097/android-pinch-zoom-and-panning-for-canvas-something-doesnt-work