Android应用:使用Activity实现一个对话框

<activity
android:name="MainApp"
android:configChanges="keyboardHidden|orientation"
android:label="@string/app_name"
android:screenOrientation="portrait"
<span style="color:#ff0000;">android:theme="@android:style/Theme.Translucent.NoTitleBar.Fullscreen" </span>>
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>

<span style="color:#33cc00;">RelativeLayout 全局layout，背景色为黑色</span>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/<span style="color:#ff0000;">screen</span>"
android:background="@color/<span style="color:#ff0000;">black</span>"
>

<span style="color:#33cc00;">LinearLayout 实际显示的layout布局，高200，靠底部显示</span>
<LinearLayout android:orientation="vertical"
android:layout_weight="1"
<span style="color:#ff0000;">android:layout_width="match_parent"
android:layout_height="200"</span>
android:layout_alignParentBottom="true">
<span style="color:#33cc00;">……
这里是具体的布局内容</span>
</LinearLayout>
</RelativeLayout>

RelativeLayout screen = (RelativeLayout)findViewById(R.id.screen);
screen.getBackground().setAlpha(70); <span style="color:#33cc00;">//参数70为透明度，取值范围为0~255，数值越小越透明</span>