Android:layout_weight's deep Understanding (Turn)

This article details the properties of Layout_weight in the Android layout, which is the weight of the remaining space .

First look at the role of the Layout_weight property: It is used to allocate a property of the remaining space, you can set his weight. Many people do not know what the remaining space is a concept, let me say the rest of the space.

1. Preliminary understanding

Let's look at the following code:

<?XML version= "1.0" encoding= "Utf-8"?>     <LinearLayoutxmlns:android= "Http://schemas.android.com/apk/res/android"android:orientation= "vertical"Android:layout_width= "Fill_parent"Android:layout_height= "Fill_parent"         >         <EditTextAndroid:layout_width= "Fill_parent"Android:layout_height= "Wrap_content"android:gravity= "Left"Android:text= "One"/>         <EditTextAndroid:layout_width= "Fill_parent"Android:layout_height= "Wrap_content"android:gravity= "Center"Android:layout_weight= "1.0"Android:text= "both"/>    <EditTextAndroid:layout_width= "Fill_parent"Android:layout_height= "Wrap_content"android:gravity= "Right"Android:text= "three"/>     </LinearLayout>   

View Code

The operating result is:

Look at the code above: only EditText2 uses the Layout_weight attribute and assigns values to 1, while EditText1 and EditText3 are not set, according to the API, they are 0 by default.

Layout_weight the real meaning of this property:

The Android system is based on the 3 EditText height layout_height values you set, assigning them 3 heights,

Then the rest of the screen space will be assigned to Button2, because only his weight value is 1, which is why Button2 accounted for such a large piece of space.

Now we have a preliminary understanding of the Layout_weight attribute, and we'll learn more about it below.

2. Further information

Let's look at the following code:

 <? XMLversion= "1.0"encoding= "UTF-8"? >    <LinearLayoutxmlns:android= "Http://schemas.android.com/apk/res/android"Android:layout_width= "Fill_parent"Android:layout_height= "Wrap_content"android:orientation= "Horizontal" >            <TextViewAndroid:background= "#ff0000"Android:layout_width="**"Android:layout_height= "Wrap_content"Android:text= "1"Android:textcolor= "@android:color/white"Android:layout_weight= "1"/>            <TextViewAndroid:background= "#cccccc"Android:layout_width="**"Android:layout_height= "Wrap_content"Android:text= "2"Android:textcolor= "@android:color/black"Android:layout_weight= "2" />             <TextViewAndroid:background= "#ddaacc"Android:layout_width="**"Android:layout_height= "Wrap_content"Android:text= "3"Android:textcolor= "@android:color/black"Android:layout_weight= "3" />    </LinearLayout> 

View Code

(1) When three textview were layout_width="wrap_content " and Layout_weight were three , you get the following effect:

(is the remaining space 1:2:3)

According to the above understanding, the system first assigns to 3 TextView their width value wrap_content (width enough to contain their content), and then the remaining space according to the 1:2:3 column assigned to 3 TextView, so the above image appears.

(2) When three TextView are layout_width="fill_parent" and Layout_weight are 1, 2 respectively, 2 O'Clock , you will get the following effect:

you will find that the weight of 1 is small, but more points, this is why??? According to the above understanding we analyze:

The system assigns 3 TextView the width fill_parent they want, which is the width of the screen.

Then the remaining space ra=1 a parent_width-3 parent_width=-2 parent_width (Parent_width refers to the screen width)

Then the actual width of the first TextView =parent_width + 1/5 * ( -2 parent_width) =3/5parent_width

Similarly the actual width of the second TextView =parent_width + 2/5* ( -2parent_width) =1/5parent_width;

The actual width of the third TextView =parent_width + 2/5* ( -2parent_width) =1/5parent_width;

So it's 3:1:1 's Billy Show.

(3) When three TextView are layout_width="fill_parent" and Layout_weight are 1 respectively ,2,3 , you get the following effect:

The third one directly does not show, why? Let's take a look at the above method to calculate it:

Remaining Space =parent_width-3*parent_width=-2 a parent_width

The actual width of the first TextView =parent_width +1/6* ( -2parent_width) =2/3parent_width;

The actual width of the second TextView =parent_width +2/6* ( -2parent_width) =1/3parent_width;

The actual width of the third TextView =parent_width +3/6* ( -2parent_width) =0parent_width;

So it's 2:1:0 's Billy Show. The third one has no space.

Transferred from: http://mobile.51cto.com/abased-375428.htm

Android:layout_weight's deep Understanding (Turn)