# CartesianMarker [`CartesianMarker`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-cartesian-marker/) instances highlight points on charts. There are two types: * Standard markers are shown on tap. These are added to a chart via the `marker` constructor parameter. * Persistent markers are shown permanently at given *x*-values. These are added to a chart via the `persistentMarkers` constructor parameter. There are two ways of creating `CartesianMarker` instances: * using [`DefaultCartesianMarker`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-default-cartesian-marker/), described below * creating a custom implementation of the interface ## `DefaultCartesianMarker` A common means of creating `CartesianMarker` instances is [`DefaultCartesianMarker`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-default-cartesian-marker/), which accepts three main components—a label, a point indicator, and a vertical line—and offers several customization options. `DefaultCartesianMarker` label text is created by [`DefaultCartesianMarker.ValueFormatter`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-default-cartesian-marker/-value-formatter/). A dedicated formatting contract is required here because `CartesianMarker` instances can highlight multiple points at once. The general principle is the same as with [`CartesianValueFormatter`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.data/-cartesian-value-formatter/), but the required information must first be [retrieved from `targets`](#cartesianmarker.target). A base `DefaultCartesianMarker.ValueFormatter` implementation can be instantiated via [`DefaultCartesianMarker.ValueFormatter.default`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-default-cartesian-marker/-value-formatter/-companion/default). This implementation uses `DecimalFormat` to format *y*-values. You can provide a custom `DecimalFormat` instance and toggle the color-coding of *y*-values. The former enables you not only to change how the *y*-values themselves are formatted, but also to add prefixes and suffixes. `DefaultCartesianMarker` is open for subclassing. ## `CartesianMarkerVisibilityListener` You can listen for visibility changes of standard markers via [`CartesianMarkerVisibilityListener`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-cartesian-marker-visibility-listener/). ## `CartesianMarkerController` By default, a standard marker appears on press and disappears on release. You can customize this with [`CartesianMarkerController`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-cartesian-marker-controller/), which has built-in implementations instantiated via the following: * [`CartesianMarkerController.showOnPress`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-cartesian-marker-controller/-companion/show-on-press) (default) * [`CartesianMarkerController.toggleOnTap`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-cartesian-marker-controller/-companion/toggle-on-tap) * [`CartesianMarkerController.showOnHover`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-cartesian-marker-controller/-companion/show-on-hover) For more specific behavior, create a custom implementation. ## `CartesianMarker.Target` `CartesianMarker` instances use [`CartesianMarker.Target`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-cartesian-marker/-target/) instances, which hold information on the highlighted points. They are stored in lists (called `targets`), since several points may be highlighted at once. `CartesianMarker.Target` itself includes only general properties. More data is found in its implementations, each of which corresponds to a [`CartesianLayer`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.layer/-cartesian-layer/): [`CandlestickCartesianLayerMarkerTarget`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-candlestick-cartesian-layer-marker-target/), [`ColumnCartesianLayerMarkerTarget`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-column-cartesian-layer-marker-target/), and [`LineCartesianLayerMarkerTarget`](https://api.vico.patrykandpatrick.com/vico/views/com.patrykandpatrick.vico.views.cartesian.marker/-line-cartesian-layer-marker-target/). In general, you should take the following approach when working with `targets`: * If you know that only one point can be highlighted at once, use `targets.first()`. (This occurs when each point has a unique pixel *x*-coordinate—for example, when only a single-series `LineCartesianLayerMarkerTarget` is present.) Otherwise, iterate `targets`. * If you know that only one kind of `CartesianMarker.Target` is present, use casting. (This occurs when only one kind of `CartesianLayer` is in use.) Otherwise, use type checking (`when` with `is`). --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://guide.vico.patrykandpatrick.com/views/cartesian-charts/cartesianmarker.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.