how can i set maximum and minimum zooming levels for image in android?

问题

I have image zooming and dragging in my application my requirement is the image sets maximum and minimum zooming levels. I have used the below code.

public class Touch extends Activity implements OnTouchListener {
   private static final String TAG = "Touch";
   // These matrices will be used to move and zoom image
   Matrix matrix = new Matrix();
   Matrix savedMatrix = new Matrix();

   // We can be in one of these 3 states
   static final int NONE = 0;
   static final int DRAG = 1;
   static final int ZOOM = 2;
   int mode = NONE;

   static final float MAX_ZOOM = 5.0f;
   static final float MIN_ZOOM = 1.0f;

   // Remember some things for zooming
   PointF start = new PointF();
   PointF mid = new PointF();
   float oldDist = 1f;

   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.findstation);
      ImageView view = (ImageView) findViewById(R.id.imageView);
      view.setOnTouchListener(this);
   }

   @Override
   public boolean onTouch(View v, MotionEvent event) {
      ImageView view = (ImageView) v;

      // Dump touch event to log
      dumpEvent(event);

      // Handle touch events here...
      switch (event.getAction() & MotionEvent.ACTION_MASK) {
      case MotionEvent.ACTION_DOWN:
         savedMatrix.set(matrix);
         start.set(event.getX(), event.getY());
         Log.d(TAG, "mode=DRAG");
         mode = DRAG;
         break;
      case MotionEvent.ACTION_POINTER_DOWN:
         oldDist = spacing(event);
         Log.d(TAG, "oldDist=" + oldDist);
         if (oldDist > 10f) {
            savedMatrix.set(matrix);
            midPoint(mid, event);
            mode = ZOOM;
            Log.d(TAG, "mode=ZOOM");
         }
         break;
      case MotionEvent.ACTION_UP:
      case MotionEvent.ACTION_POINTER_UP:
         mode = NONE;
         Log.d(TAG, "mode=NONE");
         break;
      case MotionEvent.ACTION_MOVE:
         if (mode == DRAG) {
            // ...
            matrix.set(savedMatrix);
            matrix.postTranslate(event.getX() - start.x,
                  event.getY() - start.y);
         }
         else if (mode == ZOOM) {
            float newDist = spacing(event);
            Log.d(TAG, "newDist=" + newDist);
            if (newDist > 10f) {
               matrix.set(savedMatrix);
               float scale = newDist / oldDist;


               matrix.postScale(scale, scale, mid.x, mid.y);
            }
         }
         break;
      }

      view.setImageMatrix(matrix);
      return true; // indicate event was handled
   }

   /** Show an event in the LogCat view, for debugging */
   private void dumpEvent(MotionEvent event) {
      String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
            "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
      StringBuilder sb = new StringBuilder();
      int action = event.getAction();
      int actionCode = action & MotionEvent.ACTION_MASK;
      sb.append("event ACTION_").append(names[actionCode]);
      if (actionCode == MotionEvent.ACTION_POINTER_DOWN
            || actionCode == MotionEvent.ACTION_POINTER_UP) {
         sb.append("(pid ").append(
               action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
         sb.append(")");
      }
      sb.append("[");
      for (int i = 0; i < event.getPointerCount(); i++) {
         sb.append("#").append(i);
         sb.append("(pid ").append(event.getPointerId(i));
         sb.append(")=").append((int) event.getX(i));
         sb.append(",").append((int) event.getY(i));
         if (i + 1 < event.getPointerCount())
            sb.append(";");
      }
      sb.append("]");
      Log.d(TAG, sb.toString());
   }

   /** Determine the space between the first two fingers */
   private float spacing(MotionEvent event) {
      float x = event.getX(0) - event.getX(1);
      float y = event.getY(0) - event.getY(1);
      return FloatMath.sqrt(x * x + y * y);
   }

   /** Calculate the mid point of the first two fingers */
   private void midPoint(PointF point, MotionEvent event) {
      float x = event.getX(0) + event.getX(1);
      float y = event.getY(0) + event.getY(1);
      point.set(x / 2, y / 2);
   }
}   

Can you please tell me how to set the max and min levels for zooming?

回答1:

Hi you need to define maximum zooming level

private static final float MIN_ZOOM = 1.0f;
private static final float MAX_ZOOM = //set Maximum zooming level

float scale = Math.max(MIN_ZOOM, Math.min(scale, MAX_ZOOM));

回答2:

That solution does not work, cause scale is relative value, but MIN_ZOOM and MAX_ZOOM are absolute. I've solved this problem like this:

public class GestureImageView extends ImageView {
private static final float MIN_DISTANCE_FOR_ZOOM = 5f;
private static final float MAX_SCALE_RATIO = 5f;
private static final int SCALE_X_INDEX = 0;
private static final int MATRIX_SIZE = 9;
private static final int NONE = 0;
private static final int DRAG = 1;
private static final int ZOOM = 2;
private int mode = NONE;
private GestureDetector gestureDetector;
private Matrix fitScreenMatrix = new Matrix();
private Matrix defaultMatrix = new Matrix();
private Matrix matrix = new Matrix();
private Matrix savedMatrix = new Matrix();
private PointF start = new PointF(0, 0);
private PointF mid = new PointF(0, 0);
private float oldDist = 1f;
private float minScale;
private float maxScale;


public GestureImageView(Context context) {
    super(context);

    gestureDetector = new GestureDetector(context, new DoubleTapListener());
    setOnTouchListener(new ZoomDragListener());
    setScaleType(AsyncGestureImageView.ScaleType.MATRIX);
}

private void calculateDefaultValues(Drawable drawable) {
    float imgWidth    = drawable.getIntrinsicWidth();
    float imgHeight   = drawable.getIntrinsicHeight();
    float width = getWidth();
    float height = getHeight();

    float widthRatio  = width / imgWidth;
    float heightRatio = height / imgHeight;

    float values[] = new float[MATRIX_SIZE];
    float ratio;
    PointF fitScreenPosition;
    PointF defaultPosition = new PointF((width - imgWidth)/2f, (height - imgHeight)/2f);

    if ( widthRatio < heightRatio ) {
        ratio = widthRatio;
        fitScreenPosition = new PointF(0f, (height/ratio-imgHeight)/2f);
    } else {
        ratio = heightRatio;
        fitScreenPosition = new PointF((width/ratio - imgWidth)/2f, 0f);
    }

    fitScreenMatrix.postTranslate(fitScreenPosition.x, fitScreenPosition.y);
    fitScreenMatrix.postScale(ratio, ratio, 0, 0);
    fitScreenMatrix.getValues(values);
    defaultMatrix.postTranslate(defaultPosition.x, defaultPosition.y);

    maxScale = values[SCALE_X_INDEX] * MAX_SCALE_RATIO;
    minScale = values[SCALE_X_INDEX];
}

private void fitScreen() {
    matrix.set(fitScreenMatrix);
    setImageMatrix(matrix);
}

private void defaultScreen() {
    matrix.set(defaultMatrix);
    setImageMatrix(matrix);
}

private class DoubleTapListener extends GestureDetector.SimpleOnGestureListener {
    @Override
    public boolean onDoubleTap(MotionEvent e) {
        if ( isFitScreen() ) {
            defaultScreen();
            return true;
        }
        fitScreen();
        return true;
    }
}

public boolean isFitScreen() {
    return matrix.equals(fitScreenMatrix);
}

private class ZoomDragListener implements OnTouchListener {
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        gestureDetector.onTouchEvent(event);
        AsyncGestureImageView i = (AsyncGestureImageView) v;
        dragAndZoom(i, event);

        return true;
    }

    private void dragAndZoom(View v, MotionEvent event) {
        AsyncGestureImageView view = (AsyncGestureImageView) v;

        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                savedMatrix.set(matrix);
                start.x = event.getX();
                start.y = event.getY();
                if (isFitScreen()) {
                    return;
                }
                mode = DRAG;
                break;

            case MotionEvent.ACTION_UP:

            case MotionEvent.ACTION_POINTER_UP:
                mode = NONE;
                break;

            case MotionEvent.ACTION_POINTER_DOWN:
                oldDist = gestureDistance(event);
                if (oldDist > MIN_DISTANCE_FOR_ZOOM) {
                    savedMatrix.set(matrix);
                    midPoint(mid, event);
                    mode = ZOOM;

                }
                break;

            case MotionEvent.ACTION_MOVE:
                if (mode == DRAG){
                    matrix.set(savedMatrix);
                    matrix.postTranslate((event.getX() - start.x), (event.getY() - start.y));

                } else if (mode == ZOOM) {
                    float newDist = gestureDistance(event);

                    if (newDist > MIN_DISTANCE_FOR_ZOOM) {
                        matrix.set(savedMatrix);

                        float scale = newDist / oldDist;
                        float values[] = new float[MATRIX_SIZE];
                        matrix.getValues(values);
                        float currentScale = values[SCALE_X_INDEX];
                        float newScale = currentScale * scale;

                        if ( newScale > maxScale ) {
                            scale = maxScale / currentScale;
                        }
                        if ( newScale < minScale ) {
                            scale = minScale / currentScale;
                        }

                        matrix.postScale(scale, scale, mid.x, mid.y);
                    }
                }
                break;
        }

        view.setImageMatrix(matrix);

    }

    private float gestureDistance(MotionEvent event) {
        if ( event.getPointerCount() != 2 ) {
            return 0;
        }
        float x = event.getX(0) - event.getX(1);
        float y = event.getY(0) - event.getY(1);

        return FloatMath.sqrt(x * x + y * y);
    }

    private void midPoint(PointF point, MotionEvent event) {
        point.x = event.getX(0) / 2 + event.getX(1) / 2;
        point.y = event.getY(0) / 2 + event.getY(1) / 2;
    }
}

@Override
public void setImageDrawable(Drawable drawable) {
    if ( drawable != null ) {
        calculateDefaultValues(drawable);
        fitScreen();
    }
    super.setImageDrawable(drawable);
}

来源：https://stackoverflow.com/questions/8656739/how-can-i-set-maximum-and-minimum-zooming-levels-for-image-in-android