# Interface IIOMetadataController

public interface IIOMetadataController
An interface to be implemented by objects that can determine the settings of an `IIOMetadata` object, either by putting up a GUI to obtain values from a user, or by other means. This interface merely specifies a generic `activate` method that invokes the controller, without regard for how the controller obtains values (i.e., whether the controller puts up a GUI or merely computes a set of values is irrelevant to this interface).

Within the `activate` method, a controller obtains initial values by querying the `IIOMetadata` object's settings, either using the XML DOM tree or a plug-in specific interface, modifies values by whatever means, then modifies the `IIOMetadata` object's settings, using either the `setFromTree` or `mergeTree` methods, or a plug-in specific interface. In general, applications may expect that when the `activate` method returns `true`, the `IIOMetadata` object is ready for use in a write operation.

Vendors may choose to provide GUIs for the `IIOMetadata` subclasses they define for a particular plug-in. These can be set up as default controllers in the corresponding `IIOMetadata` subclasses.

Alternatively, an algorithmic process such as a database lookup or the parsing of a command line could be used as a controller, in which case the `activate` method would simply look up or compute the settings, call methods on `IIOMetadata` to set its state, and return `true`.

See Also:
  - `IIOMetadata.setController(javax.imageio.metadata.IIOMetadataController)`
  - `IIOMetadata.getController()`
  - `IIOMetadata.getDefaultController()`
  - `IIOMetadata.hasController()`
  - `IIOMetadata.activateController()`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `boolean`
  `activate(IIOMetadata metadata)`
  Activates the controller.

- ## Method Details

  - ### activate

    boolean activate(IIOMetadata metadata)
    Activates the controller. If `true` is returned, all settings in the `IIOMetadata` object should be ready for use in a write operation. If `false` is returned, no settings in the `IIOMetadata` object will be disturbed (i.e., the user canceled the operation).
    Parameters:
      `metadata` - the `IIOMetadata` object to be modified.
    Returns:
      `true` if the `IIOMetadata` has been modified, `false` otherwise.
    Throws:
      `IllegalArgumentException` - if `metadata` is `null` or is not an instance of the correct class.