章节4-12
因为解决不了问题，SquareLayout和cell_gallary的代码直接copy老师的了。

XML如下：

<com.example.common.widget.SquareLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="1dp"
    android:background="@color/white">

    <ImageView
        android:id="@+id/im_image"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:contentDescription="@string/app_name">
    </ImageView>

    <View
        tools:visibility="visible"
        android:visibility="gone"
        android:id="@+id/view_shade"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/black_alpha_112">
    </View>
    
    <CheckBox
        tools:visibility="visible"
        android:visibility="gone"
        android:id="@+id/cb_select"
        android:layout_width="22dp"
        android:layout_height="22dp"
        android:button="@drawable/sel_cb_circle"
        android:clickable="false"
        android:drawablePadding="0dp"
        android:enabled="false"
        android:padding="0dp"
        android:layout_gravity="end"
        android:layout_margin="@dimen/len_2"
        >
    </CheckBox>

</com.example.common.widget.SquareLayout>

但是界面却是这样：