Android Shadow Layout

Hi, in current implementation of ShadowLayout it looks like it suppose to recreate its shadow background on every size change:

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    if(w > 0 && h > 0) {
        setBackgroundCompat(w, h);
    }
}

Lets say we have a TextView with string "Long label" inside the ShadowLayout, both measured as wrap_content. After child is measured ShadowLayout will generate shadow bitmap matching the size of text.

When we change the text to "Very long label" measuring phase is triggered again so the onSizeChanged of ShadowLayout will be triggered. Bigger shadow background will be created for wider label and everything is fine.

However when we would change text to "Label", TextView will be smaller, but overall width of ShadowLayout is a maximum of "largest child's width" and "background width". Since there is already old background set (rendered for wider child) - ShadowLayout will keep the original size and won't recreate the shadow background for smaller child.

We need to override following methods to let ShadowLayout ignore its current background when measuring self:

@Override
protected int getSuggestedMinimumWidth() {
    return 0;
}

@Override
protected int getSuggestedMinimumHeight() {
    return 0;
}

Here is the original implementation from View class:

protected int getSuggestedMinimumWidth() {
    return (mBackground == null) ? mMinWidth : max(mMinWidth, mBackground.getMinimumWidth());
}

protected int getSuggestedMinimumHeight() {
    return (mBackground == null) ? mMinHeight : max(mMinHeight, mBackground.getMinimumHeight());
}

It was not possible to create a new ShadowLayout programmatically passwing parameters built from an xml style. The constructor initView(Context context, AttributeSet attrs, int defStyledRes)

was doing the same as

initView(Context context, AttributeSet attrs)

This pull request consists of:

1. Setters and getters for all parameters (this also fixes issue #14)
2. The ability to automatically create round shadow (instead of setting cornerRadius to the child's width/height). Now it can be easily set with sl_round attribute. It's especially usable for Views that have their dimensions set in runtime.
3. Improved round shadow drawing (now it's possible to draw ellipse shadow).

Additionally I corrected the improperly named xml file consisting of custom attributes.

@dmytrodanylyk I created a new pull_request of these changes but for de dev branch, is this what you meant?

Thanks for this fantastic library btw.

It was not possible to create a new ShadowLayout programmatically passwing parameters built from an xml style. The constructor initView(Context context, AttributeSet attrs, int defStyledRes)

was doing the same as

initView(Context context, AttributeSet attrs)

Some notes:

Updated build tools and target API versions.

Added NonNull and Nullable annotations. Fixed NullPointerException when calling constructor without attributes.

Added missing Lollipop constructor

setBackground() is supported by 16+ while you used setBackgroundDrawable on <= 16 thus calling deprecated API on API level 16. So I inverted to >= 16 and swapped methods. Also added SuppressLint("NewApi") to avoid lint error.

According to source code obtainStyledAttributes can't return null, so the method is annotated and NonNull and null check removed. Not sure why you need that proxy method anyway but I left it.

I just make two small change to this library:

1. Bitmap.Config is ALPHA_8 before, this will make shadow color invalid, so I change it to ARGB_4444, and allow use opaque color draw shadow.
2. Cause shadow layer can not preview in xml, so I directly set the background shadow color in edit mode.