初学layout_weight疑问，求教！

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A.xml、B.xml两个布局文件，layout_weight设置不同但是运行后效果完全相同，但是实在不明白为什么layout_weight小的反而控件越大！

运行效果：

A.xml


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

  <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal" >

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="3"
            android:orientation="vertical" >

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal" >

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="9" />

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="0" />

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="C" />

            </LinearLayout>

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal" >

                <Button
                    android:layout_width="0dp"
                    android:layout_height="wrap_content"
                    android:layout_weight="2"
                    android:text="E" />

                <Button
                    android:layout_width="0dp"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="M" />

            </LinearLayout>

        </LinearLayout>

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:orientation="horizontal" >

            <Button
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:text="C" />

        </LinearLayout>
        
    </LinearLayout>
    
</LinearLayout>

B.xml


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

  <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal" >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:orientation="vertical" >

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal" >

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="9" />

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="0" />

                <Button
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="C" />

            </LinearLayout>

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal" >

                <Button
                    android:layout_width="0dp"
                    android:layout_height="wrap_content"
                    android:layout_weight="2"
                    android:text="E" />

                <Button
                    android:layout_width="0dp"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="M" />

            </LinearLayout>

        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="3"
            android:orientation="horizontal" >

            <Button
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:text="C" />
        </LinearLayout>

    </LinearLayout>
    

</LinearLayout>

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