What does android:layout_weight mean?

Question

I don't understand how to use this attribute. Can anyone tell me more about it?

Answer 1

For additional：

For vertical orientation, don't forget set height to 0dp

android:layout_height="0dp"

For horizontal orientation, don't forget set width to 0dp

android:layout_width="0dp"

Answer 2

http://developer.android.com/guide/topics/ui/layout-objects.html#linearlayout

layout_weight defines how much space the control must obtain respectively to other controls.

Answer 3

As the name suggests, Layout weight specifies what amount or percentage of space a particular field or widget should occupy the screen space.
If we specify weight in horizontal orientation, then we must specify layout_width = 0px.
Similarly, If we specify weight in vertical orientation, then we must specify layout_height = 0px.

Answer 4

In a nutshell, layout_weight specifies how much of the extra space in the layout to be allocated to the View.

LinearLayout supports assigning a weight to individual children. This attribute assigns an "importance" value to a view, and allows it to expand to fill any remaining space in the parent view. Views' default weight is zero.

Calculation to assign any remaining space between child

In general, the formula is:

space assigned to child = (child's individual weight) / (sum of weight of every child in Linear Layout)

Example 1

If there are three text boxes and two of them declare a weight of 1, while the third one is given no weight (0), then remaining space is assigned as follows:

1st text box = 1/(1+1+0)

2nd text box = 1/(1+1+0)

3rd text box = 0/(1+1+0)

Example 2

Let's say we have a text label and two text edit elements in a horizontal row. The label has no layout_weight specified, so it takes up the minimum space required to render. If the layout_weight of each of the two text edit elements is set to 1, the remaining width in the parent layout will be split equally between them (because we claim they are equally important).

Calculation:

1st label = 0/(0+1+1)

2nd text box = 1/(0+1+1)

3rd text box = 1/(0+1+1)

If, instead, the first one text box has a layout_weight of 1, and the second text box has a layout_weight of 2, then one third of the remaining space will be given to the first, and two thirds to the second (because we claim the second one is more important).

Calculation:

1st label = 0/(0+1+2)

2nd text box = 1/(0+1+2)

3rd text box = 2/(0+1+2)

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Source article

Answer 5

adding to the other answers, the most important thing to get this to work is to set the layout width (or height) to 0px

android:layout_width="0px"

otherwise you will see garbage

Answer 6

layout_weight tells Android how to distribute your Views in a LinearLayout. Android then first calculates the total proportion required for all Views that have a weight specified and places each View according to what fraction of the screen it has specified it needs. In the following example, Android sees that the TextViews have a layout_weight of 0 (this is the default) and the EditTexts have a layout_weight of 2 each, while the Button has a weight of 1. So Android allocates 'just enough' space to display tvUsername and tvPassword and then divides the remainder of the screen width into 5 equal parts, two of which are allocated to etUsername, two to etPassword and the last part to bLogin:

<LinearLayout android:orientation="horizontal" ...>

    <TextView android:id="@+id/tvUsername" 
    android:text="Username" 
    android:layout_width="wrap_content" ... />

    <EditText android:id="@+id/etUsername"
    android:layout_width="0dp"
    android:layout_weight="2" ... />

    <TextView android:id="@+id/tvPassword"
    android:text="Password"
    android:layout_width="wrap_content" />

    <EditText android:id="@+id/etPassword"
    android:layout_width="0dp"
    android:layout_weight="2" ... />

    <Button android:id="@+id/bLogin"
    android:layout_width="0dp"
    android:layout_weight="1"
    android:text="Login"... />

</LinearLayout>

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