Compose modifiers

Stay organized with collections Save and categorize content based on your preferences.

Modifiers allow you to decorate or augment a composable. Modifiers let you do these sorts of things:

  • Change the composable's size, layout, behavior, and appearance
  • Add information, like accessibility labels
  • Process user input
  • Add high-level interactions, like making an element clickable, scrollable, draggable, or zoomable

Modifiers are standard Kotlin objects. Create a modifier by calling one of the Modifier class functions:

import androidx.compose.ui.Modifier

@Composable
private fun Greeting(name: String) {
  Column(modifier = Modifier.padding(24.dp)) {
    Text(text = "Hello,")
    Text(text = name)
  }
}

Two lines of text on a colored background, with padding around the text.

You can chain these functions together to compose them:

@Composable
private fun Greeting(name: String) {
  Column(modifier = Modifier
    .padding(24.dp)
    .fillMaxWidth()
  ) {
    Text(text = "Hello,")
    Text(text = name)
  }
}

The colored background behind the text now extends the full width of the device.

In the code above, notice different modifier functions used together.

  • padding puts space around an element.
  • fillMaxWidth makes the composable fill the maximum width given to it from its parent.

It's a best practice to have all of your Composables accept a modifier parameter, and pass that modifier to its first child that emits UI. Doing so makes your code more reusable and makes its behavior more predictable and intuitive. For more information, see the Compose API guidelines, Elements accept and respect a Modifier parameter.

Order of modifiers matters

The order of modifier functions is significant. Since each function makes changes to the Modifierreturned by the previous function, the sequence affects the final result. Let's see an example of this:

@Composable
fun ArtistCard(/*...*/) {
    val padding = 16.dp
    Column(
        Modifier
            .clickable(onClick = onClick)
            .padding(padding)
            .fillMaxWidth()
    ) {
        // rest of the implementation
    }
}

The entire area, including the padding around the edges, responds to clicks

In the code above the whole area is clickable, including the surrounding padding, because the padding modifier has been applied after the clickable modifier. If the modifiers order is reversed, the space added by padding does not react to user input:

@Composable
fun ArtistCard(/*...*/) {
    val padding = 16.dp
    Column(
        Modifier
            .padding(padding)
            .clickable(onClick = onClick)
            .fillMaxWidth()
    ) {
        // rest of the implementation
    }
}

The padding around the edge of the layout no longer responds to clicks

Built-in modifiers

Jetpack Compose provides a list of built-in modifiers to help you decorate or augment a composable. Here are some common modifiers you'll use to adjust your layouts.

padding and size

By default, layouts provided in Compose wrap their children. However, you can set a size by using the size modifier:

@Composable
fun ArtistCard(/*...*/) {
    Row(
        modifier = Modifier.size(width = 400.dp, height = 100.dp)
    ) {
        Image(/*...*/)
        Column { /*...*/ }
    }
}

Note that the size you specified might not be respected if it does not satisfy the constraints coming from the layout's parent. If you require the composable size to be fixed regardless of the incoming constraints, use the requiredSize modifier:

@Composable
fun ArtistCard(/*...*/) {
    Row(
        modifier = Modifier.size(width = 400.dp, height = 100.dp)
    ) {
        Image(
            /*...*/
            modifier = Modifier.requiredSize(150.dp)
        )
        Column { /*...*/ }
    }
}

Child image is bigger than the constraints coming from its parent

In this example, even with the parent height set to 100.dp, the height of the Image will be 150.dp, as the requiredSize modifier takes precedence.

If you want a child layout to fill all the available height allowed by the parent, add the fillMaxHeight modifier (Compose also provides fillMaxSize and fillMaxWidth):

@Composable
fun ArtistCard(/*...*/) {
    Row(
        modifier = Modifier.size(width = 400.dp, height = 100.dp)
    ) {
        Image(
            /*...*/
            modifier = Modifier.fillMaxHeight()
        )
        Column { /*...*/ }
    }
}

The image height is as big as its parent

To add padding all around an element, set a padding modifier.

If you want to add padding above a text baseline such that you achieve a specific distance from the top of the layout to the baseline, use the paddingFromBaseline modifier:

@Composable
fun ArtistCard(artist: Artist) {
    Row(/*...*/) {
        Column {
            Text(
                text = artist.name,
                modifier = Modifier.paddingFromBaseline(top = 50.dp)
            )
            Text(artist.lastSeenOnline)
        }
    }
}

Text with padding above it

Offset

To position a layout relative to its original position, add the offset modifier and set the offset in the x and y axis. Offsets can be positive as well as non-positive. The difference between padding and offset is that adding an offset to a composable does not change its measurements:

@Composable
fun ArtistCard(artist: Artist) {
    Row(/*...*/) {
        Column {
            Text(artist.name)
            Text(
                text = artist.lastSeenOnline,
                modifier = Modifier.offset(x = 4.dp)
            )
        }
    }
}

Text shifted to the right side of its parent container

The offset modifier is applied horizontally according to the layout direction. In a left-to-right context, a positive offset shifts the element to the right, while in a right-to-left context, it shifts the element to the left. If you need to set an offset without considering layout direction, see the absoluteOffset modifier, in which a positive offset value always shifts the element to the right.

The offset modifier provides two overloads - offset that takes the offsets as parameters and offset that takes in a lambda. For more in depth information on when to use each of these and how to optimize for performance, read through the Compose performance - Defer reads as long as possible section.

Type safety in Compose

In Compose, there are modifiers that only work when applied to children of certain composables. For example, if you want to make a child as big as the parent Box without affecting the Box size, use the matchParentSize modifier.

Compose enforces this type safety by means of custom scopes. For example, matchParentSize is only available in BoxScope. Therefore, it can only be used when the child is used within a Box.

Scoped modifiers notify the parent about some information the parent should know about the child. These are also commonly referred to as parent data modifiers. Their internals are different from the general purpose modifiers, but from a usage perspective, these differences don't matter.

matchParentSize in Box

As mentioned above, if you want a child layout to be the same size as a parent Box without affecting the Box size, use the matchParentSize modifier.

Note that matchParentSize is only available within a Box scope, meaning that it only applies to direct children of Box composables.

In the example below, the child Spacer takes its size from its parent Box, which in turn takes its size from the biggest children, ArtistCard in this case.

@Composable
fun MatchParentSizeComposable() {
    Box {
        Spacer(Modifier.matchParentSize().background(Color.LightGray))
        ArtistCard()
    }
}

Gray background filling its container

If fillMaxSize were used instead of matchParentSize, the Spacer would take all the available space allowed to the parent, in turn causing the parent to expand and fill all the available space.

Gray background filling the screen

weight in Row and Column

As you have seen in the previous section on Padding and size, by default, a composable size is defined by the content it is wrapping. You can set a composable size to be flexible within its parent using the weight Modifier that is only available in RowScope, and ColumnScope.

Let’s take a Row that contains two Box composables. The first box is given twice the weight of the second, so it's given twice the width. Since the Row is 210.dp wide, the first Box is 140.dp wide, and the second is 70.dp:

@Composable
fun ArtistCard(/*...*/) {
    Row(
        modifier = Modifier.fillMaxWidth()
    ) {
        Image(
            /*...*/
            modifier = Modifier.weight(2f)
        )
        Column(
            modifier = Modifier.weight(1f)
        ) {
            /*...*/
        }
    }
}

The image width is twice text width

Extracting and reusing modifiers

Multiple modifiers can be chained together to decorate or augment a composable. This chain is created via the Modifier interface which represents an ordered, immutable list of single Modifier.Elements.

Each Modifier.Element represents an individual behavior, like layout, drawing and graphics behaviors, all gesture-related, focus and semantics behaviors, as well as device input events. Their ordering matters: modifier elements that are added first will be applied first.

Sometimes it can be beneficial to reuse the same modifier chain instances in multiple composables, by extracting them into variables and hoisting them into higher scopes. It can improve code readability or help improve your app's performance for a few reasons:

  • The re-allocation of the modifiers won’t be repeated when recomposition occurs for composables that use them
  • Modifier chains could potentially be very long and complex, so reusing the same instance of a chain can alleviate the workload Compose runtime needs to do when comparing them
  • This extraction promotes code cleanliness, consistency and maintainability across the codebase

Best practices for reusing modifiers

Create your own Modifier chains and extract them to reuse them on multiple composable components. It is completely fine to just save a modifier, as they are data-like objects:

val reusableModifier = Modifier
                        .fillMaxWidth()
                        .background(Color.Red)
                        .padding(12.dp)

Extracting and reusing modifiers when observing frequently changing state

When observing frequently changing states inside composables, like animation states or scrollState, there can be a significant amount of recompositions done. In this case, your modifiers will get allocated on every recomposition and potentially for every frame:

@Composable
fun LoadingWheelAnimation() {
    val animatedState = animateFloatAsState(...)

    LoadingWheel(
        // Creation and allocation of this modifier will happen on every frame of the animation!
        modifier = Modifier
            .padding(12.dp)
            .background(Color.Gray),
        animatedState = animatedState.value
    )
}

Instead, you can create, extract and reuse the same instance of the modifier and pass it to the composable like this:

// Now, the allocation of the modifier happens here:
val reusableModifier = Modifier
            .padding(12.dp)
            .background(Color.Gray)

@Composable
fun LoadingWheelAnimation() {
    val animatedState = animateFloatAsState(...)

    LoadingWheel(
        // No allocation, as we're just reusing the same instance
        modifier = reusableModifier,
        animatedState = animatedState.value
    )
}

Extracting and reusing unscoped modifiers

Modifiers can be unscoped or scoped to a specific composable. In the case of unscoped modifiers, you can easily extract them outside of any composables as simple variables:

val reusableModifier = Modifier
    .fillMaxWidth()
    .background(Color.Red)
    .padding(12.dp)

@Composable
fun AuthorField() {
    HeaderText(
        // ...
        modifier = reusableModifier
    )
    SubtitleText(
        // ...
        modifier = reusableModifier
    )
}

This can be especially beneficial when combined with Lazy layouts. In most cases, you’d want all of your, potentially significant, amount of items to have the exact same modifiers:

val reusableItemModifier = Modifier
    .padding(bottom = 12.dp)
    .size(216.dp)
    .clip(CircleShape)

@Composable
private fun AuthorList(authors: List<Author>) {
    LazyColumn {
        items(authors) {
            AsyncImage(
                // ...
                modifier = reusableItemModifier,
            )
        }
    }
}

Extracting and reusing scoped modifiers

When dealing with modifiers that are scoped to certain composables, you can extract them to the highest possible level and reuse where appropriate:

Column(...) {
    val reusableItemModifier = Modifier
        .padding(bottom = 12.dp)
        // Align Modifier.Element requires a ColumnScope
        .align(Alignment.CenterHorizontally)
        .weight(1f)
    Text1(
        modifier = reusableItemModifier,
        // ...
    )
    Text2(
        modifier = reusableItemModifier
        // ...
    )
        // ...
 }

You should only be passing the extracted, scoped modifiers to the same-scoped, direct children. You can read through the section Type safety in Compose for more reference on why this matters:

Column(modifier = Modifier.fillMaxWidth()) {
    // Weight modifier is scoped to the Column composable
    val reusableItemModifier =  Modifier.weight(1f)

    // Weight will be properly assigned here since this Text is a direct child of Column
    Text(
        modifier = reusableItemModifier
        // ...
    )

    Box {
        Text(
            // Weight won't do anything here since the Text composable is not a direct child of Column
            modifier = reusableItemModifier
            // ...
        )
    }
}

Further chaining of extracted modifiers

You can further chain or append your extracted modifier chains by calling the .then() function:

val reusableModifier = Modifier
    .fillMaxWidth()
    .background(Color.Red)
    .padding(12.dp)

// Append to your reusableModifier
reusableModifier.clickable { … }

// Append your reusableModifier
otherModifier.then(reusableModifier)

Just keep in mind that the order of modifiers matters!

Learn more

We provide a full list of modifiers, with their parameters and scopes.

For more practice on how to use modifiers, you can also go through the Basic layouts in Compose codelab or refer to the Now in Android repository.

For more information on custom modifiers and how to create them, take a look at the documentation on Custom layouts - Using the layout modifier.