Layout with Flexbox

A component can specify the layout of its children using the flexbox algorithm. Flexbox is designed to provide a consistent layout on different screen sizes.

You will normally use a combination of flexDirection, alignItems, and justifyContent to achieve the right layout.

Flexbox works the same way in React Native as it does in CSS on the web, with a few exceptions. The defaults are different, with flexDirection defaulting to column instead of row, and the flex parameter only supporting a single number.

Flex

flex will define how your items are going to “fill” over the available space along your main axis. Space will be divided according to each element's flex property.

In the following example the red, yellow and the green views are all children in the container view that has flex: 1 set. The red view uses flex: 1 , the yellow view uses flex: 2 and the green view uses flex: 3 . 1+2+3 = 6 which means that the red view will get 1/6 of the space, the yellow 2/6 of the space and the green 3/6 of the space.

Flex Direction

flexDirection controls the direction in which the children of a node are laid out. This is also referred to as the main axis. The cross axis is the axis perpendicular to the main axis, or the axis which the wrapping lines are laid out in.

• row Align children from left to right. If wrapping is enabled then the next line will start under the first item on the left of the container.

• column (default value) Align children from top to bottom. If wrapping is enabled then the next line will start to the left first item on the top of the container.

• row-reverse Align children from right to left. If wrapping is enabled then the next line will start under the first item on the right of the container.

• column-reverse Align children from bottom to top. If wrapping is enabled then the next line will start to the left first item on the bottom of the container.

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Layout Direction

Layout direction specifies the direction in which children and text in a hierarchy should be laid out. Layout direction also affects what edge start and end refer to. By default React Native lays out with LTR layout direction. In this mode start refers to left and end refers to right.

• LTR (default value) Text and children are laid out from left to right. Margin and padding applied the start of an element are applied on the left side.

• RTL Text and children are laid out from right to left. Margin and padding applied the start of an element are applied on the right side.

Justify Content

justifyContent describes how to align children within the main axis of their container. For example, you can use this property to center a child horizontally within a container with flexDirection set to row or vertically within a container with flexDirection set to column.

• flex-start(default value) Align children of a container to the start of the container's main axis.

• flex-end Align children of a container to the end of the container's main axis.

• center Align children of a container in the center of the container's main axis.

• space-between Evenly space of children across the container's main axis, distributing remaining space between the children.

• space-around Evenly space of children across the container's main axis, distributing remaining space around the children. Compared to space-between using space-around will result in space being distributed to the beginning of the first child and end of the last child.

• space-evenly Evenly distributed within the alignment container along the main axis. The spacing between each pair of adjacent items, the main-start edge and the first item, and the main-end edge and the last item, are all exactly the same.

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Align Items

alignItems describes how to align children along the cross axis of their container. Align items is very similar to justifyContent but instead of applying to the main axis, alignItems applies to the cross axis.

• stretch (default value) Stretch children of a container to match the height of the container's cross axis.

• flex-start Align children of a container to the start of the container's cross axis.

• flex-end Align children of a container to the end of the container's cross axis.

• center Align children of a container in the center of the container's cross axis.

• baseline Align children of a container along a common baseline. Individual children can be set to be the reference baseline for their parents.

For stretch to have an effect, children must not have a fixed dimension along the secondary axis. In the following example, setting alignItems: stretch does nothing until the width: 50 is removed from the children.

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Align Self

alignSelf has the same options and effect as alignItems but instead of affecting the children within a container, you can apply this property to a single child to change its alignment within its parent. alignSelf overrides any option set by the parent with alignItems.

Align Content

alignContent defines the distribution of lines along the cross-axis. This only has effect when items are wrapped to multiple lines using flexWrap.

• flex-start (default value) Align wrapped lines to the start of the container's cross axis.

• flex-end Align wrapped lines to the end of the container's cross axis.

• stretch wrapped lines to match the height of the container's cross axis.

• center Align wrapped lines in the center of the container's cross axis.

• space-between Evenly space wrapped lines across the container's main axis, distributing remaining space between the lines.

• space-around Evenly space wrapped lines across the container's main axis, distributing remaining space around the lines. Compared to space between using space around will result in space being distributed to the begining of the first lines and end of the last line.

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Flex Wrap

The flexWrap property is set on containers and controls what happens when children overflow the size of the container along the main axis. By default children are forced into a single line (which can shrink elements). If wrapping is allowed items are wrapped into multiple lines along the main axis if needed.

When wrapping lines alignContent can be used to specify how the lines are placed in the container. learn more here

Flex Basis, Grow, and Shrink

• flexGrow describes how any space within a container should be distributed among its children along the main axis. After laying out its children, a container will distribute any remaining space according to the flex grow values specified by its children.

  flexGrow accepts any floating point value >= 0, with 0 being the default value. A container will distribute any remaining space among its children weighted by the child’s flex grow value.

• flexShrink describes how to shrink children along the main axis in the case that the total size of the children overflow the size of the container on the main axis. Flex shrink is very similar to flex grow and can be thought of in the same way if any overflowing size is considered to be negative remaining space. These two properties also work well together by allowing children to grow and shrink as needed.

  Flex shrink accepts any floating point value >= 0, with 1 being the default value. A container will shrink its children weighted by the child’s flex shrink value.

• flexBasis is an axis-independent way of providing the default size of an item along the main axis. Setting the flex basis of a child is similar to setting the width of that child if its parent is a container with flexDirection: row or setting the height of a child if its parent is a container with flexDirection: column. The flex basis of an item is the default size of that item, the size of the item before any flex grow and flex shrink calculations are performed.

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Width and Height

The width property in Yoga specifies the width of the element's content area. Similarly height property specifies the height of the element's content area.

Both width and height can take following values:

• auto Is the default Value, React Native calculates the width/height for the element based on its content, whether that is other children, text, or an image.

• pixels Defines the width/height in absolute pixels. Depending on other styles set on the component, this may or may not be the final dimension of the node.

• percentage Defines the width or height in percentage of its parent's width or height respectively.

Absolute & Relative Layout

The position type of an element defines how it is positioned within its parent.

relative (default value) By default an element is positioned relatively. This means an element is positioned according to the normal flow of the layout, and then offset relative to that position based on the values of top, right, bottom, and left. The offset does not affect the position of any sibling or parent elements.

absolute When positioned absolutely an element doesn't take part in the normal layout flow. It is instead laid out independent of its siblings. The position is determined based on the top, right, bottom, and left values.

Going Deeper

Check out the interactive yoga playground that you can use to get a better understanding of flexbox.

We've covered the basics, but there are many other styles you may need for layouts. The full list of props that control layout is documented here.

We're getting close to being able to build a real application. One thing we are still missing is a way to take user input, so let's move on to learn how to handle text input with the TextInput component.

See some examples from Wix Engineers: