如何以編程方式更改按鈕樣式

Question

我在Style.xml中定義了兩種樣式，我想針對某些條件以編程方式更改樣式，Min SDK版本21

<style name="CheckOutButtonStyle" parent="@style/Widget.AppCompat.Button.Colored">
        <item name="android:layout_height">60dp</item>
        <item name="android:fontFamily">sans-serif-medium</item>
        <item name="android:textSize">16sp</item>
        <item name="android:padding">0dp</item>
        <item name="android:textColor">@color/white_color</item>
        <item name="android:layout_margin">@dimen/general_spacing</item>
    </style>


    <style name="ScanNextItemSecondaryButtonStyle" parent="@style/Widget.AppCompat.Button.Borderless">
        <item name="android:layout_height">wrap_content</item>
        <item name="android:fontFamily">sans-serif-medium</item>
        <item name="android:stateListAnimator">@null
        </item> <!-- remove the shadow, per UI request -->
        <item name="android:textSize">16sp</item>
        <item name="android:padding">0dp</item>
        <item name="android:minHeight">0dp</item>
        <item name="android:minWidth">0dp</item>
        <item name="android:background">@null</item>
        <item name="android:textColor">@color/colorSecondaryAccent</item>
        <item name="android:layout_marginBottom">@dimen/general_spacing</item>
    </style

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);