Use a command with one UI component

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You can define a command for use with one UI component in your BlackBerry® device application. Using this approach, you don't need to define metadata for the command. The core UI components for BlackBerry device applications that support commands include menu items, buttons, pop-up menu items, and toolbars.

Import the required classes and interfaces.

import net.rim.device.api.command.*;
import net.rim.device.api.ui.*;
import net.rim.device.api.ui.container.*;

Create a command handler by creating a class that extends the abstract CommandHandler class. In execute(), define the functionality that you want to associate with the UI component. To specify whether a command is executable for a given context object, you can implement a canExecute() method in your command handler. If you don't implement canExecute(), your command is always executable.
```
// this command is always executable
class DialogCommandHandler extends CommandHandler
{
   public void execute(ReadOnlyCommandMetadata metadata, Object context)
   {
      Dialog.alert("Executing command for " + context.toString());
   }
}
```

Create the UI component.

MenuItem myItem = new MenuItem(new StringProvider("My Menu Item"), 
   0x230000, 0);

For a menu item or button, you can optionally set the context for the command using the UI component's setCommandContext() method. For some commands, a context might be needed to determine what the command should do. If you don't set a context, the menu item object or button object is the context.
```
myItem.setCommandContext(new Object()
{
   public String toString()
   {
      return "My MenuItem Object"; 
   }          
});
```
Invoke setCommand() to specify the command for the UI component and provide the command handler as the method's argument.
```
myItem.setCommand(new Command(new DialogCommandHandler()));
```
Add the component to your screen.
```
addMenuItem(myItem);
```

The command is executed when a BlackBerry device user performs an action on the UI component (for example, when the user clicks a menu item).

Code samples

For examples of this approach to defining and using commands, see the API reference for MenuItem and ButtonField.

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Use a command with one UI component

Code samples