有人能向我解释为什么ImageView的没有出现上述的LinearLayout？

Can someone explain to me why the ImageView is not appearing above the LinearLayout?

<RelativeLayout
    android:layout_width="fill_parent"
    android:layout_height="wrap_content">
    <LinearLayout
        android:id="@+id/rev_main"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content">
        <!-- some stuff in here -->
    </LinearLayout>
    <ImageView
        android:id="@+id/rev_arrow"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/arrow"
        android:layout_above="@id/rev_main"
        />
</RelativeLayout>

我不明白这一点。

I don't get it.

推荐答案

这发生在你指定相对于另一个布局调整。我找到了解决办法是去另一个方向。

This happens when you specify alignment relative to another layout. The solution I found was to go the other direction.

相反，说的LinearLayout是ImageView的下方。

Instead of telling the ImageView to be above the LinearLayout, tell the LinearLayout to be below the ImageView.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content">
    <LinearLayout
        android:id="@+id/rev_main"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/rev_arrow">
        <!-- some stuff in here -->
    </LinearLayout>
    <ImageView
        android:id="@+id/rev_arrow"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/arrow"
        />
</RelativeLayout>