Development of HarmonyOS Learning Road—Java UI Framework (DirectionalLayout)

DirectionalLayout

 

DirectionalLayout is an important component layout in Java UI, which is used to arrange a group of components (Component) in a horizontal or vertical direction, and can easily align the components in the layout. The combination of this layout and other layouts can realize richer layout methods.

                                                            Diagram of DirectionalLayout

Supported XML attributes

The common XML attributes of DirectionalLayout are inherited from: Component

DirectionalLayout's own XML attributes are shown in the following table:

attribute name	Chinese description	value	Value description	Use Cases
alignment	alignment	left	Indicates left alignment.	You can set the value items as listed in the table, You can also use "|" for multiple combinations. ohos:alignment ="top|left" ohos:alignment ="left"
		top	Indicates top alignment.
		right	Indicates right alignment
		bottom	Indicates bottom alignment.
		horizontal_center	Indicates horizontal center alignment.
		vertical_center	Indicates vertical center alignment.
		center	Indicates center alignment.
		start	Indicates alignment by the start.
		end	Indicates alignment by the end.
orientation	Arrangement direction of child layout	horizontal	Indicates a horizontal layout.	ohos:orientation ="horizontal"
		vertical	Indicates a vertical layout.	ohos:orientation ="vertical"
total_weight	The sum of the weights of all subviews	float type	You can directly set the floating-point value, or you can refer to the float floating-point resource.	ohos:total_weight ="2.5" ohos:total_weigh t="$float:total_weight"

The XML attributes supported by the components contained in DirectionalLayout are shown in the following table:

attribute name	Chinese description	value	Value description	Use Cases
layout_alignment	alignment	left	Indicates left alignment.	You can set the value items as listed in the table, or use "|" to make multiple combinations. ohos:layout_alignment ="top" ohos:layout_alignmen t="top|left"
		top	Indicates top alignment.
		right	Indicates right alignment
		bottom	Indicates bottom alignment.
		horizontal_center	Indicates horizontal center alignment.
		vertical_center	Indicates vertical center alignment.
		center	Indicates center alignment.
weight	proportion	float type	You can directly set the floating-point value, or you can refer to the float floating-point resource.	ohos:weight ="1" ohos:weight ="$float:weight"

Arrangement

The orientation of DirectionalLayout is divided into horizontal or vertical. Use orientation to set the arrangement of components in the layout, and the default is vertical arrangement.

vertical arrangement

Arrange three buttons vertically, the effect is as follows:

<?xml version="1.0" encoding="utf-8"?>
<DirectionalLayout
    xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:width="match_parent"
    ohos:height="match_content"
    ohos:orientation="vertical">
    <Button
        ohos:width="33vp"
        ohos:height="20vp"
        ohos:bottom_margin="3vp"
        ohos:left_margin="13vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 1"/>
    <Button
        ohos:width="33vp"
        ohos:height="20vp"
        ohos:bottom_margin="3vp"
        ohos:left_margin="13vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 2"/>
    <Button
        ohos:width="33vp"
        ohos:height="20vp"
        ohos:bottom_margin="3vp"
        ohos:left_margin="13vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 3"/>
</DirectionalLayout>

color_cyan_element.xml：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:shape="rectangle">
    <solid
        ohos:color="#00FFFD"/>
</shape>

horizontal arrangement

 The child component does not exceed the size of the layout itself 

Arrange three buttons horizontally, the effect is as follows:

<?xml version="1.0" encoding="utf-8"?>
<DirectionalLayout
    xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:width="match_parent"
    ohos:height="match_content"
    ohos:orientation="horizontal">
    <Button
        ohos:width="33vp"
        ohos:height="20vp"
        ohos:left_margin="13vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 1"/>
    <Button
        ohos:width="33vp"
        ohos:height="20vp"
        ohos:left_margin="13vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 2"/>
    <Button
        ohos:width="33vp"
        ohos:height="20vp"
        ohos:left_margin="13vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 3"/>
</DirectionalLayout>

color_cyan_element.xml：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:shape="rectangle">
    <solid
        ohos:color="#00FFFD"/>
</shape>

• Child component exceeds the size of the layout itself

DirectionalLayout will not wrap automatically, and its sub-components will be arranged in sequence according to the set direction. If it exceeds the size of the layout itself, the part exceeding the size of the layout will not be displayed.

<?xml version="1.0" encoding="utf-8"?>
<DirectionalLayout
    xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:width="match_parent"
    ohos:height="20vp"
    ohos:orientation="horizontal">
    <Button
        ohos:width="166vp"
        ohos:height="match_content"
        ohos:left_margin="13vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 1"/>
    <Button
        ohos:width="166vp"
        ohos:height="match_content"
        ohos:left_margin="13vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 2"/>
    <Button
        ohos:width="166vp"
        ohos:height="match_content"
        ohos:left_margin="13vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 3"/>
</DirectionalLayout>

 color_cyan_element.xml：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:shape="rectangle">
    <solid
        ohos:color="#00FFFD"/>
</shape>

This layout contains three buttons, but since the DirectionalLayout does not automatically wrap, the part of the component that exceeds the size of the layout cannot be displayed. The interface is displayed as follows:

alignment

 Components in DirectionalLayout use layout_alignment to control their own alignment in the layout. The alignment method is closely related to the arrangement method. When the arrangement method is horizontal, the optional alignment method only works in the vertical direction (top, bottom, vertical_center, center). Other alignment methods will not take effect. When the arrangement is vertical, the optional alignment only applies to the horizontal type (left, right, start, end, horizontal_center, center). Other alignments will not take effect.

Sample code for three alignments:

<?xml version="1.0" encoding="utf-8"?>
<DirectionalLayout
    xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:width="match_parent"
    ohos:height="60vp">
    <Button
        ohos:width="50vp"
        ohos:height="20vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:layout_alignment="left"
        ohos:text="Button 1"/>
    <Button
        ohos:width="50vp"
        ohos:height="20vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:layout_alignment="horizontal_center"
        ohos:text="Button 2"/>
    <Button
        ohos:width="50vp"
        ohos:height="20vp"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:layout_alignment="right"
        ohos:text="Button 3"/>
</DirectionalLayout>

color_cyan_element.xml：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:shape="rectangle">
    <solid
        ohos:color="#00FFFD"/>
</shape>

Example of three alignment effects

 Weights

Weight (weight) is to allocate the size of the parent component proportionally to the component. The calculation formula in the horizontal layout is:

Assignable width of parent layout = width of parent layout - sum of width of all child components;

Component width = component weight / sum of all component weights * parent layout can assign width;

In actual use, it is recommended to use width=0 to proportionally distribute the width of the parent layout. The effect of 1:1:1 is as follows:

<?xml version="1.0" encoding="utf-8"?>
<DirectionalLayout
    xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:width="match_parent"
    ohos:height="match_content"
    ohos:orientation="horizontal">
    <Button
        ohos:width="0vp"
        ohos:height="20vp"
        ohos:weight="1"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 1"/>
    <Button
        ohos:width="0vp"
        ohos:height="20vp"
        ohos:weight="1"
        ohos:background_element="$graphic:color_gray_element"
        ohos:text="Button 2"/>
    <Button
        ohos:width="0vp"
        ohos:height="20vp"
        ohos:weight="1"
        ohos:background_element="$graphic:color_cyan_element"
        ohos:text="Button 3"/>
</DirectionalLayout>

 color_cyan_element.xml：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:shape="rectangle">
    <solid
        ohos:color="#00FFFD"/>
</shape>

color_gray_element.xml：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:shape="rectangle">
    <solid
        ohos:color="#878787"/>
</shape>

Scenario example

 Source code example:

<?xml version="1.0" encoding="utf-8"?>
<DirectionalLayout
    xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:height="match_parent"
    ohos:width="match_parent"
    ohos:background_element="#FFFFFFFF">

    <DirectionalLayout
        ohos:height="70vp"
        ohos:width="match_parent"
        ohos:orientation="vertical"
        ohos:background_element="#FF9F9F9F"
        ohos:top_margin="10vp">

        <Button
            ohos:height="20vp"
            ohos:width="33vp"
            ohos:background_element="#FF00FFFD"
            ohos:bottom_margin="3vp"
            ohos:left_margin="13vp"
            ohos:text="Button 1"/>

        <Button
            ohos:height="20vp"
            ohos:width="33vp"
            ohos:background_element="#FF00FFFD"
            ohos:bottom_margin="3vp"
            ohos:left_margin="13vp"
            ohos:text="Button 2"/>

        <Button
            ohos:height="20vp"
            ohos:width="33vp"
            ohos:background_element="#FF00FFFD"
            ohos:bottom_margin="3vp"
            ohos:left_margin="13vp"
            ohos:text="Button 3"/>
    </DirectionalLayout>

    <DirectionalLayout
        ohos:height="70vp"
        ohos:width="match_parent"
        ohos:orientation="horizontal"
        ohos:background_element="#FF9F9F9F"
        ohos:top_margin="10vp"
        >

        <Button
            ohos:height="20vp"
            ohos:width="33vp"
            ohos:background_element="#FF00FFFD"
            ohos:left_margin="13vp"
            ohos:text="Button 1"/>

        <Button
            ohos:height="20vp"
            ohos:width="33vp"
            ohos:background_element="#FF00FFFD"
            ohos:left_margin="13vp"
            ohos:text="Button 2"/>

        <Button
            ohos:height="20vp"
            ohos:width="33vp"
            ohos:background_element="#FF00FFFD"
            ohos:left_margin="13vp"
            ohos:text="Button 3"/>
    </DirectionalLayout>

    <DirectionalLayout
        ohos:height="70vp"
        ohos:width="match_parent"
        ohos:orientation="horizontal"
        ohos:background_element="#FF9F9F9F"
        ohos:top_margin="10vp"
        >

        <Button
            ohos:height="match_content"
            ohos:width="166vp"
            ohos:background_element="#FF00FFFD"
            ohos:left_margin="13vp"
            ohos:text="Button 1"/>

        <Button
            ohos:height="match_content"
            ohos:width="166vp"
            ohos:background_element="#FF00FFFD"
            ohos:left_margin="13vp"
            ohos:text="Button 2"/>

        <Button
            ohos:height="match_content"
            ohos:width="166vp"
            ohos:background_element="#FF00FFFD"
            ohos:left_margin="13vp"
            ohos:text="Button 3"/>
    </DirectionalLayout>

    <DirectionalLayout
        ohos:height="70vp"
        ohos:width="match_parent"
        ohos:background_element="#FF9F9F9F"
        ohos:top_margin="10vp"
        >

        <Button
            ohos:height="20vp"
            ohos:width="50vp"
            ohos:background_element="#FF00FFFD"
            ohos:layout_alignment="left"
            ohos:text="Button 1"/>

        <Button
            ohos:height="20vp"
            ohos:width="50vp"
            ohos:background_element="#FF00FFFD"
            ohos:layout_alignment="horizontal_center"
            ohos:text="Button 2"/>

        <Button
            ohos:height="20vp"
            ohos:width="50vp"
            ohos:background_element="#FF00FFFD"
            ohos:layout_alignment="right"
            ohos:text="Button 3"/>
    </DirectionalLayout>

    <DirectionalLayout
        ohos:height="70vp"
        ohos:width="match_parent"
        ohos:orientation="horizontal"
        ohos:background_element="#FF9F9F9F"
        ohos:top_margin="10vp"
        >

        <Button
            ohos:height="20vp"
            ohos:width="0vp"
            ohos:background_element="#FF00FFFD"
            ohos:text="Button 1"
            ohos:weight="1"/>

        <Button
            ohos:height="20vp"
            ohos:width="0vp"
            ohos:background_element="#FFFF8A8A"
            ohos:text="Button 2"
            ohos:weight="1"/>

        <Button
            ohos:height="20vp"
            ohos:width="0vp"
            ohos:background_element="#FF00FFFD"
            ohos:text="Button 3"
            ohos:weight="1"/>
    </DirectionalLayout>
</DirectionalLayout>