Android中设置半个屏幕大小且居中的button布局 (layout_weight属性)

        先看例如以下布局 ： 

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" alt="" />

上图中。按钮的大小为屏幕的一半，然后居中显示在布局中央，每一个人心中都有自己的答案，看看我的方法吧，布局布局xml例如以下 ：

<?

xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:baselineAligned="false"
    android:gravity="center"
    android:orientation="horizontal"
    android:weightSum="1" >     <!-- 1.将LinearLayout的layout_weight设置为1 -->

    <!-- 2.将Button的layout_width设为0dp, 而且将layout_weight设置为0.5 -->
    <Button
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="0.5"
        android:textSize="13sp"
        android:text="@string/button_text" >
    </Button>

</LinearLayout>

这里有几个关键点：

1. 布局为LinearLayout，以便能够设置layout_weight。
2. 设置LinearLayout的android:weightSum的值为1；
3. 将Button的layout_width设置为0dp;
4. 将Button的layout_weight的值设置为0.5。 即上面的android:weightSum的一半。

通过上面的设置就能够实现上图中的布局了。

子空间的宽度算法能够參考例如以下公式， 子控件宽度 = 子控件layout_width + 子控件的layout_weight * 父控件的宽度 / 父控件的layout_weight， 对照上面的样例就是子控件的宽度 = 0.5 * 父控件的宽度 / 1 = 父控件宽度 * 0.5。 由于父控件的宽度为match_parent，所以父控件宽度的宽度为整个屏幕的宽度，所以子控件的宽度 = 0.5 * 整个屏幕的宽度 = 半屏宽度。