Можем ли мы использовать детектор жестов масштаба для масштабирования в Android?

Вы можете использовать это

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.drawable.BitmapDrawable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;

public class MyImageView extends View {

private static final int INVALID_POINTER_ID = -1;

    private Drawable mImage;
    private float mPosX;
    private float mPosY;

    private float mLastTouchX;
    private float mLastTouchY;
    private int mActivePointerId = INVALID_POINTER_ID;

    private ScaleGestureDetector mScaleDetector;
    private float mScaleFactor = 1.f;

    public MyImageView(Context context) {
        this(context, null, 0);
    mImage=act.getResources().getDrawable(context.getResources().getIdentifier("imag­ename", "drawable", "packagename"));

        mImage.setBounds(0, 0, mImage.getIntrinsicWidth(), mImage.getIntrinsicHeight());
    }

    public MyImageView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public MyImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        // Let the ScaleGestureDetector inspect all events.
        mScaleDetector.onTouchEvent(ev);

        final int action = ev.getAction();
        switch (action & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN: {
            final float x = ev.getX();
            final float y = ev.getY();

            mLastTouchX = x;
            mLastTouchY = y;
            mActivePointerId = ev.getPointerId(0);
            break;
        }

        case MotionEvent.ACTION_MOVE: {
            final int pointerIndex = ev.findPointerIndex(mActivePointerId);
            final float x = ev.getX(pointerIndex);
            final float y = ev.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 = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) 
                    >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
            final int pointerId = ev.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 = ev.getX(newPointerIndex);
                mLastTouchY = ev.getY(newPointerIndex);
                mActivePointerId = ev.getPointerId(newPointerIndex);
            }
            break;
        }
        }

        return true;
    }

    @Override
    public void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        canvas.save();
        Log.d("DEBUG", "X: "+mPosX+" Y: "+mPosY);
        canvas.translate(mPosX, mPosY);
        canvas.scale(mScaleFactor, mScaleFactor);
        mImage.draw(canvas);
        canvas.restore();
    }

    private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            mScaleFactor *= detector.getScaleFactor();

            // Don't let the object get too small or too large.
            mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 10.0f));

            invalidate();
            return true;
        }
    }

}

чтобы назвать это в вашем activity.setContentView(new MyImageView(this));

Вы можете создать многоразовый класс, который реализует OnTouchListener для достижения этой цели.

public class MyScaleGestures implements OnTouchListener, OnScaleGestureListener {       
    private View view;
    private ScaleGestureDetector gestureScale;
    private float scaleFactor = 1;  
    private boolean inScale = false;

    public MyScaleGestures (Context c){ gestureScale = new ScaleGestureDetector(c, this); }

    @Override
    public boolean onTouch(View view, MotionEvent event) {
        this.view = view; 
        gestureScale.onTouchEvent(event);
        return true;
    }   

    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        scaleFactor *= detector.getScaleFactor();
        scaleFactor = (scaleFactor < 1 ? 1 : scaleFactor); // prevent our view from becoming too small //
        scaleFactor = ((float)((int)(scaleFactor * 100))) / 100; // Change precision to help with jitter when user just rests their fingers //
        view.setScaleX(scaleFactor);
        view.setScaleY(scaleFactor);
        return true;
    }

    @Override
    public boolean onScaleBegin(ScaleGestureDetector detector) {
        inScale = true;
        return true;
    }

    @Override
    public void onScaleEnd(ScaleGestureDetector detector) { inScale = false; }
}

Затем назначьте его как OnTouchListener вашего View вот так.

myView.setOnTouchListener(new MyScaleGestures(context));

Если вы хотите добавить возможность прокрутки в View, вам нужно будет реализовать onScroll из интерфейса OnGestureListener. Для этого вы можете добавить это переопределение в класс MyScaleGestures.

@Override
public boolean onScroll(MotionEvent event1, MotionEvent event2, float x, float y) {
    float newX = view.getX();
    float newY = view.getY();
    if(!inScale){
        newX -= x;
        newY -= y;
    }
    WindowManager wm = (WindowManager) view.getContext().getSystemService(Context.WINDOW_SERVICE);
    Display d = wm.getDefaultDisplay();
    Point p = new Point();
    d.getSize(p);

    if (newX > (view.getWidth() * scaleFactor - p.x) / 2){
        newX = (view.getWidth() * scaleFactor - p.x) / 2;
    } else if (newX < -((view.getWidth() * scaleFactor - p.x) / 2)){
        newX = -((view.getWidth() * scaleFactor - p.x) / 2);
    }

    if (newY > (view.getHeight() * scaleFactor - p.y) / 2){
        newY = (view.getHeight() * scaleFactor - p.y) / 2;
    } else if (newY < -((view.getHeight() * scaleFactor - p.y) / 2)){
        newY = -((view.getHeight() * scaleFactor - p.y) / 2);
    }

    view.setX(newX);
    view.setY(newY);

    return true;
}

Конечный результат выполнения всего вышеперечисленного даст вам класс, подобный этому:

public class StandardGestures implements OnTouchListener, OnGestureListener, OnDoubleTapListener, OnScaleGestureListener {
    private View view;
    private GestureDetector gesture;
    private ScaleGestureDetector gestureScale;
    private float scaleFactor = 1;
    private boolean inScale;

    public StandardGestures(Context c){
        gesture = new GestureDetector(c, this);
        gestureScale = new ScaleGestureDetector(c, this);
    }

    @Override
    public boolean onTouch(View view, MotionEvent event) {
        this.view = view;
        gesture.onTouchEvent(event);
        gestureScale.onTouchEvent(event);
        return true;
    }

    @Override
    public boolean onDown(MotionEvent event) {
        return true;
    }

    @Override
    public boolean onFling(MotionEvent event1, MotionEvent event2, float x, float y) {
        return true;
    }

    @Override
    public void onLongPress(MotionEvent event) {
    }

    @Override
    public boolean onScroll(MotionEvent event1, MotionEvent event2, float x, float y) {
        float newX = view.getX();
        float newY = view.getY();
        if(!inScale){
            newX -= x;
            newY -= y;
        }
        WindowManager wm = (WindowManager) view.getContext().getSystemService(Context.WINDOW_SERVICE);
        Display d = wm.getDefaultDisplay();
        Point p = new Point();
        d.getSize(p);

        if (newX > (view.getWidth() * scaleFactor - p.x) / 2){
            newX = (view.getWidth() * scaleFactor - p.x) / 2;
        } else if (newX < -((view.getWidth() * scaleFactor - p.x) / 2)){
            newX = -((view.getWidth() * scaleFactor - p.x) / 2);
        }

        if (newY > (view.getHeight() * scaleFactor - p.y) / 2){
            newY = (view.getHeight() * scaleFactor - p.y) / 2;
        } else if (newY < -((view.getHeight() * scaleFactor - p.y) / 2)){
            newY = -((view.getHeight() * scaleFactor - p.y) / 2);
        }

        view.setX(newX);
        view.setY(newY);

        return true;
    }

    @Override
    public void onShowPress(MotionEvent event) {
    }

    @Override
    public boolean onSingleTapUp(MotionEvent event) {
        return true;
    }

    @Override
    public boolean onDoubleTap(MotionEvent event) {
        view.setVisibility(View.GONE);
        return true;
    }

    @Override
    public boolean onDoubleTapEvent(MotionEvent event) {
        return true;
    }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent event) {
        return true;
    }

    @Override
    public boolean onScale(ScaleGestureDetector detector) {

        scaleFactor *= detector.getScaleFactor();
        scaleFactor = scaleFactor < 1 ? 1 : scaleFactor; // prevent our image from becoming too small
        scaleFactor = (float) (int) (scaleFactor * 100) / 100; // Change precision to help with jitter when user just rests their fingers //
        view.setScaleX(scaleFactor);
        view.setScaleY(scaleFactor);
        onScroll(null, null, 0, 0); // call scroll to make sure our bounds are still ok //
        return true;
    }

    @Override
    public boolean onScaleBegin(ScaleGestureDetector detector) {
        inScale = true;
        return true;
    }

    @Override
    public void onScaleEnd(ScaleGestureDetector detector) {
        inScale = false;
        onScroll(null, null, 0, 0); // call scroll to make sure our bounds are still ok //
    }
}

ScaleGestureDetector доступен, начиная с Android 2.2 (он же Froyo, уровень API 8). См.: http://android-developers.blogspot.com/2010/06/making-sense-of-multitouch.html

В версиях 2.0/2.1 у вас нет ScaleGestureDetector, но вы можете обеспечить масштабирование, используя запись в блоге ZDNet Эда Бернетта, на которую Pieter888 ссылается выше: http://www.zdnet.com/blog/burnette/how-to-use-multi-touch-in-android-2-part-6-implementing-the-pinch-zoom-gesture/1847

на самом деле есть библиотека, которая использует этот класс только для масштабирования изображений.

он называется "TouchImageView"

TouchImageView

public class TouchImageView extends ImageView {
    Matrix 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;

    // Remember some things for zooming
    PointF last = new PointF();
    PointF start = new PointF();
    float minScale = 1f;
    float maxScale = 3f;
    float[] m;
    int viewWidth, viewHeight;

    static final int CLICK = 3;

    float saveScale = 1f;

    protected float origWidth, origHeight;

    int oldMeasuredWidth, oldMeasuredHeight;

    ScaleGestureDetector mScaleDetector;

    Context context;

    public TouchImageView(Context context) {
        super(context);
        sharedConstructing(context);
    }

    public TouchImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        sharedConstructing(context);
    }

    private void sharedConstructing(Context context) {

        super.setClickable(true);

        this.context = context;

        mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());

        matrix = new Matrix();

        m = new float[9];

        setImageMatrix(matrix);

        setScaleType(ScaleType.MATRIX);

        setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {

                mScaleDetector.onTouchEvent(event);

                PointF curr = new PointF(event.getX(), event.getY());

                switch (event.getAction()) {

                    case MotionEvent.ACTION_DOWN:

                        last.set(curr);

                        start.set(last);

                        mode = DRAG;

                        break;

                    case MotionEvent.ACTION_MOVE:

                        if (mode == DRAG) {

                            float deltaX = curr.x - last.x;

                            float deltaY = curr.y - last.y;

                            float fixTransX = getFixDragTrans(deltaX, viewWidth, origWidth * saveScale);

                            float fixTransY = getFixDragTrans(deltaY, viewHeight, origHeight * saveScale);

                            matrix.postTranslate(fixTransX, fixTransY);

                            fixTrans();

                            last.set(curr.x, curr.y);

                        }

                        break;

                    case MotionEvent.ACTION_UP:

                        mode = NONE;

                        int xDiff = (int) Math.abs(curr.x - start.x);

                        int yDiff = (int) Math.abs(curr.y - start.y);

                        if (xDiff < CLICK && yDiff < CLICK)

                            performClick();

                        break;

                    case MotionEvent.ACTION_POINTER_UP:

                        mode = NONE;

                        break;

                }

                setImageMatrix(matrix);

                invalidate();

                return true; // indicate event was handled
            }
        });
    }

    public void setMaxZoom(float x) {

        maxScale = x;
    }

    private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {

        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {

            mode = ZOOM;

            return true;
        }

        @Override
        public boolean onScale(ScaleGestureDetector detector) {

            float mScaleFactor = detector.getScaleFactor();

            float origScale = saveScale;

            saveScale *= mScaleFactor;

            if (saveScale > maxScale) {

                saveScale = maxScale;

                mScaleFactor = maxScale / origScale;

            } else if (saveScale < minScale) {

                saveScale = minScale;

                mScaleFactor = minScale / origScale;

            }

            if (origWidth * saveScale <= viewWidth || origHeight * saveScale <= viewHeight)

                matrix.postScale(mScaleFactor, mScaleFactor, viewWidth / 2, viewHeight / 2);

            else

                matrix.postScale(mScaleFactor, mScaleFactor, detector.getFocusX(), detector.getFocusY());

            fixTrans();

            return true;
        }
    }

    void fixTrans() {

        matrix.getValues(m);

        float transX = m[Matrix.MTRANS_X];

        float transY = m[Matrix.MTRANS_Y];

        float fixTransX = getFixTrans(transX, viewWidth, origWidth * saveScale);

        float fixTransY = getFixTrans(transY, viewHeight, origHeight * saveScale);

        if (fixTransX != 0 || fixTransY != 0)

            matrix.postTranslate(fixTransX, fixTransY);
    }

    float getFixTrans(float trans, float viewSize, float contentSize) {

        float minTrans, maxTrans;

        if (contentSize <= viewSize) {

            minTrans = 0;

            maxTrans = viewSize - contentSize;

        } else {

            minTrans = viewSize - contentSize;

            maxTrans = 0;

        }

        if (trans < minTrans)

            return -trans + minTrans;

        if (trans > maxTrans)

            return -trans + maxTrans;

        return 0;
    }

    float getFixDragTrans(float delta, float viewSize, float contentSize) {

        if (contentSize <= viewSize) {

            return 0;

        }

        return delta;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        viewWidth = MeasureSpec.getSize(widthMeasureSpec);

        viewHeight = MeasureSpec.getSize(heightMeasureSpec);

        //
        // Rescales image on rotation
        //
        if (oldMeasuredHeight == viewWidth && oldMeasuredHeight == viewHeight

                || viewWidth == 0 || viewHeight == 0)

            return;

        oldMeasuredHeight = viewHeight;

        oldMeasuredWidth = viewWidth;

        if (saveScale == 1) {

            //Fit to screen.

            float scale;

            Drawable drawable = getDrawable();

            if (drawable == null || drawable.getIntrinsicWidth() == 0 || drawable.getIntrinsicHeight() == 0)

                return;

            int bmWidth = drawable.getIntrinsicWidth();

            int bmHeight = drawable.getIntrinsicHeight();

            Log.e("bmSize", "bmWidth: " + bmWidth + " bmHeight : " + bmHeight);

            float scaleX = (float) viewWidth / (float) bmWidth;

            float scaleY = (float) viewHeight / (float) bmHeight;

            scale = Math.min(scaleX, scaleY);

            matrix.setScale(scale, scale);

            // Center the image

            float redundantYSpace = (float) viewHeight - (scale * (float) bmHeight);

            float redundantXSpace = (float) viewWidth - (scale * (float) bmWidth);

            redundantYSpace /= (float) 2;

            redundantXSpace /= (float) 2;

            matrix.postTranslate(redundantXSpace, redundantYSpace);

            origWidth = viewWidth - 2 * redundantXSpace;

            origHeight = viewHeight - 2 * redundantYSpace;

            setImageMatrix(matrix);

        }

        fixTrans();
    }
}

MainActivity.java

public class SecondActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);


        TouchImageView img = new TouchImageView(this);
        img.setImageResource(R.drawable.ic_launcher);
        img.setMaxZoom(4f);
        setContentView(img);
    }
}

да, мы можем вот пример кода, где onPinch() и onZoom() - это действия, которые нужно реализовать самостоятельно

public class simpleOnScaleGestureListener extends
        SimpleOnScaleGestureListener {

    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        startScale = detector.getScaleFactor();
        return true;
    }

    @Override
    public boolean onScaleBegin(ScaleGestureDetector detector) {
        return true;
    }

    @Override
    public void onScaleEnd(ScaleGestureDetector detector) {
        endScale = detector.getScaleFactor();



        if (startScale > endScale) {
            Log.i("onScaleEnd", "Pinch Dection");
            onPinch();
        } else if (startScale < endScale) {
            Log.i("onScaleEnd", "Zoom Dection");
            onZoom();
        }


    }

}