How to get height of LinearLayout

I have a LinearLayout set height as match_parent as below:

<LinearLayout
    android:id="@+id/list_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

I want to get the height of this LinearLayout.
I used the code below:

LinearLayout ll_list = (LinearLayout)findViewById(R.id.list_layout);
int h = ll_list.getHeight();

But it return null.
How can I do?