Bug with Android 4.3 ImageView method getImageMatrix()

问题

I recently upgraded to Android 4.4 and someone of the features of my app have surprisingly stopped working.

I have this code for initializing and then drawing my custom view. The basic idea is it adjusts the zoom level so the entire view fits on the screen.

private void initAtZoomLevel(float zoomLevel){
    ....
    Matrix transformMatrix = new Matrix();
    transformMatrix.setScale(initialZoomLevel, initialZoomLevel);
    float yTransCenter = (screenHeight - mapHeight)/2.0f;
    setImageMatrix(transformMatrix);
}

protected void onDraw(Canvas canvas){

    super.onDraw(canvas);
    float[] values = new float[9];
    getImageMatrix().getValues(values);
    scaleFactor = values[0];
    ....
}

THIS WORKS ON ANDROID 4.1.2, and 4.2.2 DEVICES I HAVE

But on Android 4.4/4.3 getImageMatrix().getValues(values) stopped working! It returns an identity matrix instead of the transform matrix I expect on app start up!

DEBUG PRINT-OUT:

4.1.2: @setImageMatrix(transformMatrix): transformMatrix = Matrix{[0.025122833, 0.0, 0.0][0.0, 0.025122833, 566.5][0.0, 0.0, 1.0]}

@getImageMatrix().getValues(values): transformMatrix = Matrix{[0.025122833, 0.0, 0.0][0.0, 0.025122833, 566.5][0.0, 0.0, 1.0]}

4.4: @setImageMatrix(transformMatrix): transformMatrix = Matrix{[0.025122833, 0.0, 0.0][0.0, 0.025122833, 553.0][0.0, 0.0, 1.0]}

@getImageMatrix().getValues(values): transformMatrix = Matrix{[1.0, 0.0, 0.0][0.0, 1.0, 0.0][0.0, 0.0, 1.0]}

I've looked around and I can't seem to find any documentation on this. Somehow the image matrix for my view is being reset; has Android 4.4 changed the way we are supposed to do this? Has anyone else run in to this problem?

note: the problem appears to have originated on Android 4.3 - the same problem occurs running on an emulator

UPDATE: I have checked the change log from 4.2 to 4.3, but there is nothing on there I can see above the Matrix Class, or anything relevant to the View class.

UPDATE 2: My pinch-to-zoom is also not working, which uses the same setImageMatrix() method - and it's clearly not sticking because nothing happens in getImageMatrix().getValues()

回答1:

I have found what I believe to be the problem. I took a look at the source code for ImageView and discovered the setImageMatrix(Matrix matrix) is saving the matrix in a different field than getImageMatrix() is returning...

Android 4.4 ImageView

public void setImageMatrix(Matrix matrix) {
    // collaps null and identity to just null
    if (matrix != null && matrix.isIdentity()) {
        matrix = null;
    }

    // don't invalidate unless we're actually changing our matrix
    if (matrix == null && !mMatrix.isIdentity() ||
            matrix != null && !mMatrix.equals(matrix)) {
        mMatrix.set(matrix);
        configureBounds();
        invalidate();
    }
}

Here the matrix is being stored in the field mMatrix

public Matrix getImageMatrix() {
    if (mDrawMatrix == null) { //<-- should be mMatrix == null
        return new Matrix(Matrix.IDENTITY_MATRIX);
    }
    return mDrawMatrix; //<-- NOT THE RIGHT FIELD TO RETURN
}

While getImageMatrix() returns mDrawMatrix...

Android 4.1.2 ImageView

public Matrix getImageMatrix() {
    return mMatrix;
}

public void setImageMatrix(Matrix matrix) {
    // collaps null and identity to just null
    if (matrix != null && matrix.isIdentity()) {
        matrix = null;
    }

    // don't invalidate unless we're actually changing our matrix
    if (matrix == null && !mMatrix.isIdentity() ||
            matrix != null && !mMatrix.equals(matrix)) {
        mMatrix.set(matrix);
        configureBounds();
        invalidate();
    }
}

both methods use the same field - mMatrix

So there's the problem right there --- all of a sudden getImageMatrix() is returning the wrong field...

回答2:

While my previous answer does outline the overall problem, it in fact might not be a bug. As pointed out by Generic Holiday Name, mDrawMatrix should be set to mMatrix in the configureBounds() method - which would eliminate this problem/bug/whatever.

HOWEVER, I had to add several lines of code to get configureBounds() to actually work:

private void configureBounds() {
    if (mDrawable == null || !mHaveFrame) {
        return;
    }

    int dwidth = mDrawableWidth;
    int dheight = mDrawableHeight;

    ...

    if (dwidth <= 0 || dheight <= 0 || ScaleType.FIT_XY == mScaleType) {
        /* If the drawable has no intrinsic size, or we're told to
            scaletofit, then we just fill our entire view.
        */
        mDrawable.setBounds(0, 0, vwidth, vheight);
        mDrawMatrix = null;
    } else {
             //here's the where mDrawMatrix == mMatrix IF using scaleType.MATRIX
             ...
    }
}

---

So, in order to actually get this to work the way I expect with 4.2 and below you need to make sure:

1. mDrawable != null. This wasn't a problem before, but for my case I wasn't using a drawable so everything was failing (the return statement was hit right away)
2. 'dwidth >0 && dheight >0. This isn't a problem if you have a real drawable, but like I said, I didn't.
3. mHaveFrame = true. I had no idea what this was - never used it. The only way to set this to true is by calling setFrame(int, int, int, int).

To get my scaling code to work again, I had to add the following:

 //potentially a fix for the "bug" that appears in Android 4.3+
 //mDrawable cannot be null anymore for getImageMatrix to work---stupid
 //therefore the imageview class MUST set a drawable for matrix scaling to work
 //so here I am using a "empty" drawable to get around this
 ShapeDrawable fakeDrawable = new ShapeDrawable(); //so mDrawable != null
 fakeDrawable.setIntrinsicHeight(1); //so dwidth and dheight are > 0
 fakeDrawable.setIntrinsicWidth(1);

 setImageDrawable(fakeDrawable);

 setFrame(0, 0, viewWidth, viewHeight); //setting a frame so mHaveFrame = true

YIKES

来源：https://stackoverflow.com/questions/20431374/bug-with-android-4-3-imageview-method-getimagematrix