Trouble with ImageView gravity on Java, Android

I have this code:

<LinearLayout 
    android:layout_weight="0.5" 
    android:layout_width="0px" 
    android:id="@+id/linearLayout2" 
    android:orientation="vertical" 
    android:layout_height="fill_parent">
<LinearLayout 
    android:layout_weight="0.45" 
    android:layout_width="fill_parent" 
    android:id="@+id/linearLayoutMainLogo" 
    android:orientation="horizontal"
    android:gravity="center" 
    android:layout_height="0px">
    <ImageView 
        android:src="@drawable/logo" 
        android:layout_gravity="center"
开发者_运维技巧        android:layout_width="wrap_content" 
        android:id="@+id/imageViewLogo" 
        android:layout_height="wrap_content" />
</LinearLayout>
</LinearLayout>

I need to set ImageView in center of LinearLayout by horizontal and by vertical simultaneously, but my code doesn't work. Where did I do mistake? Thank you

This is wrong i think: android:layout_width="0px" android:layout_height="0px"

Just correct with this:

<LinearLayout 
    android:layout_width="fill_parent" 
    android:id="@+id/linearLayout2" 
    android:orientation="vertical" 
    android:layout_height="fill_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">
<LinearLayout 
    android:layout_weight="0.45" 
    android:layout_width="fill_parent" 
    android:id="@+id/linearLayoutMainLogo" 
    android:orientation="horizontal"
    android:gravity="center" 
    android:layout_height="wrap_content">
    <ImageView 
        android:src="@drawable/icon" 
        android:gravity="center"
        android:layout_width="wrap_content" 
        android:id="@+id/imageViewLogo" 
        android:layout_height="wrap_content" />
</LinearLayout>
</LinearLayout>