<?xml version="1.0" encoding="utf-8"?>

 <shape xmlns:android="http://schemas.android.com/apk/res/android">

   <!--设置渐变颜色 angle=""是从左到右  90是从上到下  180是从右到左 -->

     <gradient

         android:startColor="#4169E1"

         android:endColor="#E6E6FA"

         android:angle="" />

     <stroke

         android:width="2dp"

         android:color="#D2691E"

         />

     <corners android:radius="10dip"/>

     <padding

         android:left="10dp"

            android:top="10dp"

               android:right="10dp"

                  android:bottom="10dp"

         />

 </shape>

 <?xml version="1.0" encoding="utf-8"?>

 <shape xmlns:android="http://schemas.android.com/apk/res/android">

   <!-- angle=""是从左到右  90是从上到下  180是从右到左 且必须是45的倍数 -->

     <gradient

         android:startColor="#FFD700"

         android:endColor="#f5deb3"

         android:angle="" />

     <stroke

         android:width="2dp"

         android:color="#FFB6C1"

         />

     <corners android:radius="20dip"/>

     <padding

         android:left="10dp"

            android:top="10dp"

               android:right="10dp"

                  android:bottom="10dp"

         />

 </shape>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:gravity="center"

    android:background="@drawable/asdf"

    tools:context="com.example.top5_4.MainActivity" >

<Button

    android:id="@+id/but"

     android:layout_height="wrap_content"

     android:layout_width="wrap_content"

     android:text="点击按钮改变按钮样式"

     android:background="@drawable/round"

    />

</LinearLayout>

 public class MainActivity extends Activity {

 private Button but;

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super.onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

        but=(Button) findViewById(R.id.but);

     but.setOnClickListener(new OnClickListener() {

         @Override

         public void onClick(View v) {

             // TODO Auto-generated method stub

             //点击后更改按钮样式

             but.setBackgroundResource(R.drawable.newround);

              //另外设置按钮的透明度setAlpha()里面的值大小为0~255

             but.getBackground().setAlpha();

         }

     });

     }

 }