The role and use of layout_weight in the child of Android--linearlayout

When a child with weight is included in the LinearLayout, LinearLayout will measure two times:

First measure the original value of the child:

The second measurement of a child's specific gravity value:

The value of the 2 measurements is then added to get the specific width or height of the child.

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We assume that a linearlayout direction is horizontal android:orientation= "horizontal", which has 2 child, child_1 and Child_2, respectively.

Let's analyze how the values of these 2 child widths are calculated with the Layout_weight attribute.

The first measurement: has its own layout_width parameter decision

First, the child's width (layout_width) has 3 cases: 0DP (specific values, can be set arbitrarily, such as 100DP), Wrap_content, Match_parent.

In these 3 cases, when the application is loaded on a specific phone, it will be measured to a specific value, as follows:

1, when Child_1 's Layout_width is 0DP, its width_orginal original width is 0pix; (100DP, then width_orginal for screen density density * pix = x_1 pix)

(where the cell phone screen density is through context.getresources (). Getdisplaymetrics (). Density get)

2, when Child_1 's Layout_width is wrap_content, its width_orginal original width is int_wrap_cotent (on the specific phone is a fixed value, assuming x_1 pix);

3, when Child_1 's Layout_width is match_parent, its width_orginal original width for the width of the phone screen (on the specific phone is a fixed value, assuming x_1 pix);

(The original width of the child_2 is x_2)

Second measurement: All child's layout_weight parameters are determined together

Assume that the layout_weight of the 2 child are weight_1 and weight_2 (the Layout_weight parameter is an int type value, which can be 0):

Then the final width of child_1 and child_2 is:

Child_1 width: x_1 + (Phone screen width-(x_1 + x_2)) * Weight_1/(weight_1+weight_2) = final width.

Here are a few examples:

The layout_width of Demo1:child_1 and Child_2 are 0dp,layout_weight 1 and 2 respectively.

1 <LinearLayoutxmlns:android= "Http://schemas.android.com/apk/res/android"2 Xmlns:tools= "Http://schemas.android.com/tools"3 Android:id= "@+id/root"4 Android:layout_width= "Match_parent"5 Android:layout_height= "Match_parent"6 android:orientation= "Horizontal" >7 8     <TextView9         Android:id= "@+id/tv_left"Ten Android:layout_width= "0DP" One Android:layout_height= "Wrap_content" A Android:layout_weight= "1" - Android:background= "#00ff00" the Android:text= "Child_1" - android:textsize= "24SP" /> -  -     <TextView +         Android:id= "@+id/tv_right" - Android:layout_width= "0DP" + Android:layout_height= "Wrap_content" A Android:layout_weight= "2" at Android:background= "#ff0000" -  - Android:text= "Child_2" - android:textsize= "24SP" /> -  - </LinearLayout>

At this point, the final width of the child_1 is: 0 pix + screen width * 1/3 = 1/3 screen width. Child_2 the screen width of the final width of 2/3.

So you want to proportionally distribute the wide (high) value of the LinearLayout children, you can use the secondary method.

The layout_width of Demo2:child_1 and Child_2 are 100dp,layout_weight 1 and 2 respectively.

1 <LinearLayoutxmlns:android= "Http://schemas.android.com/apk/res/android"2 Xmlns:tools= "Http://schemas.android.com/tools"3 Android:id= "@+id/root"4 Android:layout_width= "Match_parent"5 Android:layout_height= "Match_parent"6 android:orientation= "Horizontal" >7 8     <TextView9         Android:id= "@+id/tv_left"Ten Android:layout_width= "100DP" One Android:layout_height= "Wrap_content" A Android:layout_weight= "1" - Android:background= "#00ff00" -  the Android:text= "Child_1" - android:textsize= "24SP" /> -  -     <TextView +         Android:id= "@+id/tv_right" - Android:layout_width= "100DP" + Android:layout_height= "Wrap_content" A Android:layout_weight= "2" at Android:background= "#ff0000" -  - Android:text= "Child_2" - android:textsize= "24SP" /> -  - </LinearLayout>

At this point, the final width of the child_1 is: + * density pix + (screen width-DP * density) * 1/3 = ...

The layout_width of Demo2:child_1 and Child_2 are match_parent,layout_weight 1 and 2 respectively.

1 <LinearLayoutxmlns:android= "Http://schemas.android.com/apk/res/android"2 Xmlns:tools= "Http://schemas.android.com/tools"3 Android:id= "@+id/root"4 Android:layout_width= "Match_parent"5 Android:layout_height= "Match_parent"6 android:orientation= "Horizontal" >7 8     <TextView9         Android:id= "@+id/tv_left"Ten Android:layout_width= "Match_parent" One Android:layout_height= "Wrap_content" A Android:layout_weight= "1" - Android:background= "#00ff00" -  the Android:text= "Child_1" - android:textsize= "24SP" /> -  -     <TextView +         Android:id= "@+id/tv_right" - Android:layout_width= "Match_parent" + Android:layout_height= "Wrap_content" A Android:layout_weight= "2" at Android:background= "#ff0000" -  - Android:text= "Child_2" - android:textsize= "24SP" /> -  - </LinearLayout>

At this point, the final width of the child_1 is: Screen width + (screen width-twice times the screen width) * 1/3 = 2/3 screen width, child_2 1/3 screen width.

When the layout_width of child is match_parent, want child_1:child_2 = 1:2 (i.e. 1/3:2/3), you can set the child_2 of Child_1 Layout_weight as ( Denominator-1): (Denominator-2).

When the child's layout_width are match_parent, want child_1:child_2:child_3 = 3:4: 5 (that is, 3/12:4/12:5/12), you can set the Layout_weight (12-3):(12-4):(12-5)

The role and use of layout_weight in the child of Android--linearlayout