Using layout_above in a RelativeLayout

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:开发者_如何学Golayout_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>

I don't get it.

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

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>

The following should work for you:

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

I had an similar problem by creating a custom optionsMenu. The simplest way to set z-order of views was to do it programmatically. If you want to switch the order sometimes, your should easily call:

    ImageView yourImageView = (ImageView)findViewById(R.id.rev_arrow);
    yourImageView.bringToFront();

I don´t know if it is adaptive to your application, but in my case it works perfect. If you need more code, let me know.

If you have such problem in ListView make sure that you use proper inflation method. Parent view group must be specified for correct inflation.

mLayoutInflater.inflate(R.layout.listitem, parent, false);

Don't use

mLayoutInflater.inflate(R.layout.listitem, null);