angle attribute in android gradient

Question

I am going through test example. Where for some Image background they are using gradient, the code goes like this

<?xml version="1.0" encoding="utf-8"?>     <shape xmlns:android="http://schemas.android.com/apk/res/android">     <gradient         android:startColor="#ff0000"         android:centerColor="#00ff00"         android:endColor="#0000ff"         android:angle="180"/>     <corners android:radius="5dp" />    </shape> 

In the above xml I didn't get angle attribute. but when I change the value of angle slightly the pattern slants. Can anyone explain me how exactly it works?

Answer 1

Gradient basically represents the variation in space(in a direction) of any quantity. With color it represents the variation of color intensity in a direction represented by angle. Here are some diagrams to represent this concept:

Here the figure shows the color variation in horizontal direction (angle is set 0).
XML code:

    <shape xmlns:android="http://schemas.android.com/apk/res/android">     <gradient         android:startColor="#000000"         android:angle="0"/>    </shape> 

Here the figure shows the color variation in vertical direction (angle is set 90).
XML code:

<shape xmlns:android="http://schemas.android.com/apk/res/android"> <gradient     android:startColor="#000000"     android:angle="90"/>  </shape> 

You can also use different color as start, center and end colors. The code you attached contains all these elements.