Android - 控制图像只在屏幕内移动？

Question

我正在缩放，旋转和移动图像。我希望图像在移动图像时保持在屏幕视图中。其他一切都很好。

之前已经问过这个问题，但没有答案。有什么帮助吗？

public class MainActivity extends AppCompatActivity implements View.OnTouchListener {
private ImageView img_scale;
private float mScaleFactor = 0.5f;
private float mRotationDegree = 0.f;
private float mFocusX = 0.f;
private float mFocusY = 0.f;
private int mScreenHeight;
private int mScreenWidth;
private Matrix matrix = new Matrix();
private int mImageWidth, mImageHeight;
private ScaleGestureDetector mScaleDetector;
private RotateGestureDetector mRotateDetector;
private MoveGestureDetector mMoveDetector;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    img_scale = (ImageView) findViewById(R.id.img_scale);
    img_scale.setOnTouchListener(this);
    DisplayMetrics displayMetrics = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
    mScreenHeight = displayMetrics.heightPixels;
    mScreenWidth = displayMetrics.widthPixels;

    Bitmap loadTempImg = BitmapFactory.decodeResource(getResources(), R.drawable.exercise_icon);
    mImageHeight = loadTempImg.getHeight();
    mImageWidth = loadTempImg.getWidth();
    img_scale.setImageBitmap(loadTempImg);
    matrix.postScale(mScaleFactor, mScaleFactor);
    img_scale.setImageMatrix(matrix);


    mScaleDetector = new ScaleGestureDetector(getApplicationContext(), new ScaleListener());
    mRotateDetector = new RotateGestureDetector(getApplication(), new RotateListener());
    mMoveDetector = new MoveGestureDetector(getApplication(), new MoveListener());

}

private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        mScaleFactor *= detector.getScaleFactor();
        mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 1.0f));
        return true;
    }
}

private class RotateListener extends RotateGestureDetector.SimpleOnRotateGestureListener {
    @Override
    public boolean onRotate(RotateGestureDetector detector) {
        mRotationDegree -= detector.getRotationDegreesDelta();
        return true;
    }
}

private class MoveListener extends MoveGestureDetector.SimpleOnMoveGestureListener {
    @Override
    public boolean onMove(MoveGestureDetector detector) {
        PointF d = detector.getFocusDelta();
        mFocusX += d.x;
        mFocusY += d.y;




        return true;
    }
}

@Override
public boolean onTouch(View v, MotionEvent event) {
    mScaleDetector.onTouchEvent(event);
    mRotateDetector.onTouchEvent(event);
    mMoveDetector.onTouchEvent(event);
    float scaleImageCenterX = (mImageWidth * mScaleFactor) / 2;
    float scaleImageCenterY = (mImageHeight * mScaleFactor) / 2;

    matrix.reset();
    matrix.postScale(mScaleFactor, mScaleFactor);
    matrix.postRotate(mRotationDegree, scaleImageCenterX, scaleImageCenterY);
    matrix.postTranslate(mFocusX - scaleImageCenterX, mFocusY - scaleImageCenterY);

    ImageView view = (ImageView) v;
    view.setImageMatrix(matrix);
    return true;
}
}