intellij-sdk-code-samples/topics/ui/controls/combo_box.md

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# Combo Box

<link-summary>UI guidelines on using combo boxes.</link-summary>

<tldr>

**Implementation**: [`ComboBox`](%gh-ic%/platform/platform-api/src/com/intellij/openapi/ui/ComboBox.java)

</tldr>

A combo box combines a [drop-down list](drop_down.md) and an [input field](input_field.md), allowing the user to select a value from the list or enter a custom value.

![](combo_box_example.png){width=328}

Use [`ComboBox`](%gh-ic%/platform/platform-api/src/com/intellij/openapi/ui/ComboBox.java) instead of `javax.swing.JComboBox`.
To make combo box editable invoke:

```java
comboBox.setEditable(true);
```

## When to use

Use a combo box if:

* The user needs to select a value or enter a custom value.

  ![](combo_box_font_size.png){width=165}

* The possible choices are objects or states.


* The user may need to return to previous values. For example, save previously entered paths, so the user can quickly
  select them later:

  ![](maven.png){width=413}

### When not to use

If the number of options is finite, and there’s no need to enter custom values. In this case, use a [drop-down list](drop_down.md) or [radio buttons](radio_button.md).

If it’s not possible to list the most likely choices. In this case, use an [input field](input_field.md) instead.

![](prefill.png){width=152}

If the list is big, and the user knows what value they need and won’t review the list. In this case, use an input field with completion.

![](input_field_completion.png){width=509}

## How to use

For the [label](drop_down.md#label) and the [default value](drop_down.md#default-value) apply the same rules as for the
[drop-down list](drop_down.md).

If there are no values in the list initially, replace the combo box with an input field.
This way, users won't waste their time clicking the empty combo box to find out that there are no options available.

| <format color="Red" style="bold">Incorrect</format> | <format color="Green" style="bold">Correct</format> |
|-----------------------------------------------------|-----------------------------------------------------|
| ![](combo_box_empty.png){width="221"}               | ![](replace_with_iput_field.png){width="216"}       |

Replace the input field with a combo box after a value has been entered and confirmed.

### Menu

#### Control

Open the combo box menu by clicking the arrow button on the right or pressing the <shortcut>Down</shortcut> arrow key when the combo box is focused.
The menu opens down by default. If there is not enough space, the menu opens up.

When the menu opens, select the element that was shown in the closed combo box. If a custom value is entered, then do not select a value in the list.

Move the selection in the menu and update the value in the combo box by pressing the <control>Up</control> and <control>Down</control> arrow keys.
On mouse hover, move the selection to an item the cursor is pointing to and update the value by clicking the mouse button or pressing <shortcut>Enter</shortcut>.

The menu remains opened until the user clicks the item in the list, presses <shortcut>Enter</shortcut> or <shortcut>Esc</shortcut>, clicks outside the menu,
or switches to another app.

#### Menu items

The menu list contains predefined or the most likely options. Follow the rules for [drop-down menu items](drop_down.md#menu-items).

If the user needs to return to previous inputs, add such values to the end of the list when clicking the confirmation button in the dialog.

![](maven.png){width=413}

Use [built-in buttons](built_in_button.md) to add values or expand the combo box, e.g., the browse button:

![](built_in_button.png){width=384}

## Validation

If the user enters an invalid value, highlight the combo box with red and show an error message in a tooltip. For
more details, see [Validation errors](validation_errors.md).

![](validation.png){width=235}

## Sizes and placement

Follow the [drop-down guidelines](drop_down.md#sizes-and-placement).