What is android weightSum in android and how does it work

Question

I want to know  What is android weightSum and layout weight  and how do they work

User · Accepted Answer

Per documentation  android weightSum defines the maximum weight sum  and is calculated as the sum of the layout weight of all the children if not specified explicitly   Let s consider an example with a LinearLayout with horizontal orientation and 3 ImageViews inside it  Now we want these ImageViews always to take equal space  To acheive this  you can set the layout weight of each ImageView to 1 and the weightSum will be calculated to be equal to 3 as shown in the comment    lt LinearLayout     android layout width  wrap content      android layout height  wrap content       lt  -- android weightSum  3  -- gt      android orientation  horizontal      android layout gravity  center  gt       lt ImageView        android layout height  wrap content                android layout weight  1         android layout width  0dp   gt            weightSum is useful for having the layout rendered correctly for any device  which will not happen if you set width and height directly

User · Answer

From developer documentation   This can be used for instance to give a single child 50  of the total available space by giving it a layout weight of 0 5 and setting the weightSum to 1 0   Addition to  Shubhayu answer  rest 3 5 can be used for other child layouts which really doesn t need any specific portion of containing layout    this is potential use of android weightSum property

User · Answer

One thing which seems like no one else mentioned  let s say you have a vertical LinearLayout  so in order for the weights in layout element view inside it to work 100  properly - all of them must have layout height property  which must exist in your xml file  set to 0dp  Seems like any other value would mess things up in some cases

User · Answer

After some experimenting  I think the algorithm for LinearLayout is this   Assume that weightSum is set to a value  The case of absence is discussed later   First  divide the weightSum by the number of elements whith match parent or fill parent in the dimension of the LinearLayout  e g  layout width for orientation  horizontal    We will call this value the weight multiplier  for each element  The default value for weightSum is 1 0  so the default weight multiplier is 1 n  where n is the number of fill parent elements  wrap content elements do not contribute to n     E g  when weightSum is 60  and there are 3 fill parent elements  the weight multiplier is 20  The weight multiplier is the default value for e g  layout width if the attribute is absent   Second  the maximum possible expansion of every element is computed  First  the wrap content elements are computed according to their contents  Their expansion is deducted from the expansion of the parent container  We will call the remainer expansion remainer  This remainder is distributed among fill parent elements according to their layout weight   Third  the expansion of every fill parent element is computed as     Example   If weightSum is 60  and there are 3 fill parent elements with the weigths 10  20 and 30  their expansion on the screen is 2 3  1 3 and 0 3 of the parent container   weight   expansion      0   3 3     10   2 3     20   1 3     30   0 3     40   0 3   The minimum expansion is capped at 0  The maximum expansion is capped at parent size  i e  weights are capped at 0   If an element is set to wrap content  its expansion is calculated first  and the remaining expansion is subject to distribution among the fill parent elements  If weightSum is set  this leads to layout weight having no effect on wrap content elements  However  wrap content elements can still be pushed out of the visible area by elements whose weight is lower than   e g  between 0-1 for weightSum  1 or between 0-20 for the above example    If no weightSum is specified  it is computed as the sum of all layout weight values  including elements with wrap content set  So having layout weight set on wrap content elements  can influence their expansion  E g  a negative weight will shrink the other fill parent elements  Before the fill parent elements are laid out  will the above formula be applied to wrap content elements  with maximum possible expansion being their expansion according to the wrapped content  The wrap content elements will be shrunk  and afterwards the maximum possible expansion for the remaining fill parent elements is computed and distributed   This can lead to unintuitive results

User · Answer

Layout Weight works like a ratio  For example  if there is a vertical layout and there are two items such as buttons or textviews   one having layout weight 2 and the other having layout weight 3 respectively  Then the 1st item will occupy 2 out of 5 portion of the screen layout and the other one 3 out of 5 portion  Here 5 is the weight sum  i e  Weight sum divides the whole layout into defined portions  And Layout Weight defines how much portion does the particular item occupies out of the total Weight Sum pre-defined  Weight sum can be manually declared as well  Buttons  textviews  edittexts etc all are organized using weightsum and layout weight when using linear layouts for UI design

User · Answer

Weight sum works exactly as you want  like other answers you don t have to sum all the weights on parent layout   On child view specify the weight you want it to take  Don t forget to specify   android layout width  0dp     Following is an example       lt LinearLayout                 android layout width  500dp                  android layout height  20dp   gt                    lt TextView                     android layout width  0dp                      android layout height  match parent                      android layout weight  3                      android background   android color holo green light                      android gravity  center                      android text  30                       android textColor   android color white   gt                   lt  TextView gt                    lt TextView                     android layout width  0dp                      android layout height  match parent                      android layout weight  2                      android background   android color holo blue bright                      android gravity  center                      android text  20                       android textColor   android color white   gt                   lt  TextView gt                    lt TextView                     android layout width  0dp                      android layout height  match parent                      android layout weight  5                      android background   android color holo orange dark                      android gravity  center                      android text  50                       android textColor   android color white   gt                   lt  TextView gt    lt  LinearLayout gt    This will look like

User · Answer

Adding on to superM s and Jeff s answer    If there are 2 views in the LinearLayout  the first with a layout weight of 1  the second with a layout weight of 2 and no weightSum is specified  by default  the weightSum is calculated to be 3  sum of the weights of the children  and the first view takes 1 3 of the space while the second takes 2 3   However  if we were to specify the weightSum as 5  the first would take 1 5th of the space while the second would take 2 5th  So a total of 3 5th of the space would be occupied by the layout keeping the rest empty

User · Answer

If unspecified  the sum is computed by adding the layout weight of all of the children  This can be used for instance to give a single child 50  of the total available space by giving it a layout weight of 0 5 and setting the weightSum to 1 0  Must be a floating point value  such as  1 2        lt LinearLayout xmlns android  http   schemas android com apk res android          android id    id main rel          android layout width  match parent          android layout height  match parent          android orientation  horizontal          android weightSum  2 0   gt            lt RelativeLayout             android id    id child one              android layout width  match parent              android layout height  match parent              android layout weight  1 0              android background   0000FF   gt           lt  RelativeLayout gt            lt RelativeLayout             android id    id child two              android layout width  match parent              android layout height  match parent              android layout weight  1 0              android background   00FF00   gt           lt  RelativeLayout gt        lt  LinearLayout gt

User · Answer

The documentation says it best and includes an example   highlighting mine        android weightSum      Defines the maximum weight sum  If unspecified  the sum is computed by   adding the layout weight of all of the children  This can be used for   instance to give a single child 50  of the total available space by   giving it a layout weight of 0 5 and setting the weightSum to 1 0    So to correct superM s example  suppose you have a LinearLayout with horizontal orientation that contains two ImageViews and a TextView with   You define the TextView to have a fixed size  and you d like the two ImageViews to take up the remaining space equally     To accomplish this  you would apply layout weight 1 to each ImageView  none on the TextView  and a weightSum of 2 0 on the LinearLayout

User · Answer

No one has explicitly mentioned that weightSum is a particular XML attribute for LinearLayout  I believe this would be helpful to anyone who was confused at first as I was  looking for weightSum in the ConstraintLayout documentation

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