如何以编程方式更改按钮样式

Question

我在Style.xml中定义了两种样式，我想针对某些条件以编程方式更改样式，Min SDK版本21

settings.json

Answer 1

1. Create xml in drawable. 
\res\drawable\back_button_answer.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle" >
   <corners android:radius="10dip" />
   <!-- background -->

   <gradient
                android:startColor="#D6D7D6"
                android:centerColor="#E2E2E2"
                android:centerY="0.75"
                android:endColor="#D6D7D6"
                android:angle="270"
        />

   <stroke android:width="2dip" android:color="#fff"/>
</shape>


2. Button btn.setBackgroundResource(R.drawable.back_button_answer);