Android基础TOP5_4:点击按钮更换样式，设置透明度

<?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();
}
});
}
}