What does android:layout_weight mean?

7+8+75+10 = 100
(Em phải mở PS ra để đo đó =)) )

Haha, đây này

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    android:orientation="vertical" >
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/to" />
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/subject" />
    <EditText
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:gravity="top"
        android:hint="@string/message" />
    <Button
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_gravity="right"
        android:text="@string/send" />
</LinearLayout>

Link: http://developer.android.com/guide/topics/ui/layout/linear.html

android:layout_height=“0dp”

hình như phải thêm cái này nữa mới dùng layout_weight. Height 0dp == không quan tâm height.

The problems are the circumstances it is used in. In this case it is used with layout_height set to match_parent. In some (!) cases this keeps Android from interpreting the layout_weights correctly. In this case, a vertical layout of view elements, the solution is setting layout_heights to 0dp. With a horizontal layout of view elements layout_width should be set to 0dp.

http://www.chess-ix.com/blog/the-use-of-layout_weight-with-android-layouts/

Nếu android:orientation là vertical thì layout_height phải là 0dp. Ngược lại nếu android:orientation là horizontal thì layout_width phải là 0dp

Video này nói rất rõ này