Android layout_weight comportment

I am trying to build an android layout using layout_weight to fit all sizes of devices and I have some trouble understanding its comportment.

I noticed that changing the layout_width/layout_height influenced the layout_weight comportment, but I don't understand how.

Let's say for example I want to have a vertical LinearLayout divided in three inners LinearLayout such that the one at the top and the one at the bottom are filling 25% of the screen, and the on in the middle 50%, and that should not depend of the content of the inner layouts. (If the content of a inner LinearLayout is too big, it should not shift the others layouts)

In order to do this, should I set the layout_height attribute of the inner LinearLayout to fill_parent or to wrap_content?

Thanks!

EDIT: It looks like the layout_weight is inversely proportional to the size the layout will occupate.

3 examples:

Weight 1/1/1 (working as I expected)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/mainLayout"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">
        <LinearLayout
            android:id="@+id/layout1"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_weight="1"
            android:background="#FF0000"/> //RED
        <LinearLayout
            android:id="@+id/layout2"
            android:layout_width="fill_parent"
            android:layout_heigh开发者_如何转开发t="fill_parent"
            android:layout_weight="1"
            android:background="#00FF00"/> //GREEN
        <LinearLayout
            android:id="@+id/layout3"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_weight="1"
            android:background="#0000FF"/> //BLUE
</LinearLayout>

Results:

Weight 1/2/1 (Why, oh why?)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/mainLayout"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">
        <LinearLayout
            android:id="@+id/layout1"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_weight="1"
            android:background="#FF0000"/> //RED
        <LinearLayout
            android:id="@+id/layout2"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_weight="2"
            android:background="#00FF00"/> //GREEN
        <LinearLayout
            android:id="@+id/layout3"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_weight="1"
            android:background="#0000FF"/> //BLUE
</LinearLayout>

Results:

**Weight 3/2/3 (What I entended to do with 1/2/1):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/mainLayout"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">
        <LinearLayout
            android:id="@+id/layout1"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_weight="3"
            android:background="#FF0000"/> //RED
        <LinearLayout
            android:id="@+id/layout2"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_weight="2"
            android:background="#00FF00"/> //GREEN
        <LinearLayout
            android:id="@+id/layout3"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_weight="3"
            android:background="#0000FF"/> //BLUE
</LinearLayout>

Results:

You can try to set layout_height = 0dp

For the layout_weight to work as expected (and documented) you must not set the layout_height to neither fill_parent nor match_parent.

The example to the right on http://developer.android.com/guide/topics/ui/layout/linear.html#Weight shows an example where layout_height is set to 0dp. However not setting it at all or setting it to wrap_content also makes the layout_weight work as expected.

You should set the layout_height of all three inner layouts to "fill_parent" and then change their weights to make them look like you want.