CODEWITHSUNDEEP
androidandroid-layoutdrawableandroid-5.0-lollipopnine-patch
user977289
user977289

Reputation: 57

Why Android layer-list drawable so intelligent?

I can't dig deep into how android implements its layer-list drawable. But I find it interesting and I can hardly know why this happens.

Here are some drawables:

the nine-patch xml

<?xml version="1.0" encoding="utf-8"?>
<nine-patch xmlns:android="http://schemas.android.com/apk/res/android"
android:src="@drawable/cam2tst_ripple_bg_img">
</nine-patch>

the shape xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
<padding
    android:left="@dimen/cam2tst_ripple_horizontal_padding"
    android:top="@dimen/cam2tst_ripple_vertical_padding"
    android:right="@dimen/cam2tst_ripple_horizontal_padding"
    android:bottom="@dimen/cam2tst_ripple_vertical_padding" />
<solid android:color="@android:color/holo_green_dark" />
</shape>

the ripple xml

<?xml version="1.0" encoding="utf-8"?>
<ripple xmlns:android="http://schemas.android.com/apk/res/android"
android:color="@android:color/holo_green_light">
<item android:drawable="@drawable/cam2tst_ripple_shape"></item>
</ripple>

the layer-list containing all above

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
<item android:drawable="@drawable/cam2tst_ripple_bg_img" />
<item android:drawable="@drawable/cam2tst_ripple_base" />
</layer-list>

Unfortainately I still can't get my screenshot thing work on my L preview, but I can describe it.

What I get is the shape (which i obviously didn't set its size explicitly） doesn't cover over the whole nine-patch! The un-streched part of the nine-patch is magically considered as some kind of "auto padding thing". What I was expecting (ok I was expecting exactly what android has done for me, I mean what I was... supposing...) is something not so positive: the not-particularly-sized shape drawable covering the entire nine-patch just as if the latter is a normal png.

But the shape does magically avoid the un-stretched part of the nine-patch and overlays only above the streched-part of the nine-patch.

This is awesome...but confusing, why? I may not able to dig that deep into the source but this do sounds anti-intuition (but nice). I want to know the reason though. So I post this here.

Since I tagged this as android-L because I am working on one. But I think this shall be working from something like gingerbread.(just to replace the ripple drawable with something else, maybe a inset drawable etc.)

Upvotes: 3

Views: 1369

Answers (1)

corsair992
corsair992

Reputation: 3070

This effect is caused by the combination of two things:

  1. All nine-patch drawables have a padding area defined automatically from the edges of the content area. The content area can be defined either explicitly, using the right and bottom lines at the border, or implicitly from the stretchable area defined by the left and top lines.

  2. Layer-list applies the padding on each layer cumulatively to the next layer by default*, effectively treating each layer as the content of the previous layer.

* Lollipop has introduced a new attribute for disabling this behavior.

Upvotes: 6

Related Questions