Blackberry: select an item from the list, return to the previous screen

Question

I prepared a very short test case (hereinafter) for my question.

When I click the button, I want to display a list of lines on a new screen.

After the user selects one item in the list, the previous screen should be displayed again, and the button label should be set to the selected line.

My 2 problems:

• From inside the menu, I don’t know how to put the displayed screen.
• How to transfer the selected item from one screen to another (if I do not want to enter a public variable / method on the first screen as a workaround)

Please provide the necessary changes for my src \ mypackage \ MyList.java :

package mypackage; import java.util.*; import net.rim.device.api.collection.*; import net.rim.device.api.collection.util.*; import net.rim.device.api.system.*; import net.rim.device.api.ui.*; import net.rim.device.api.ui.component.*; import net.rim.device.api.ui.container.*; import net.rim.device.api.ui.decor.*; import net.rim.device.api.util.*; import net.rim.device.internal.i18n.*; public class MyList extends UiApplication implements FieldChangeListener { MyScreen myScreen = new MyScreen(); public static void main(String args[]) { MyList app = new MyList(); app.enterEventDispatcher(); } public MyList() { MainScreen titleScreen = new MainScreen(); titleScreen.setTitle("Click the button:"); // TODO change the label of this button (see below) ButtonField myButton = new ButtonField("Show the list", ButtonField.CONSUME_CLICK); myButton.setChangeListener(this); titleScreen.add(myButton); pushScreen(titleScreen); } public void fieldChanged(Field field, int context) { pushScreen(myScreen); } } class MyScreen extends MainScreen { ObjectListField myList = new ObjectListField(); public MyScreen() { setTitle("Select an item below:"); myList.set(new String[] { "Item 1", "Item 2", "Item 3", "Item 4", }); add(myList); addMenuItem(myMenu); } private final MenuItem myMenu = new MenuItem("Select item", 0, 0) { public void run() { int index = myList.getSelectedIndex(); if (index < 0) return; String item = (String) myList.get(myList, index); Status.show("Selected: " + item); // TODO how to return to the previous screen here? // TODO how to call myButton.setLabel(item) here? } }; } 

Thanks! Alex

Answer 1

Use the callback template:

 class TitleScreen extends MainScreen { private ButtonField myButton; public TitleScreen() { super(); setTitle("Click the button:"); // TODO change the label of this button (see below) myButton = new ButtonField("Show the list", ButtonField.CONSUME_CLICK); myButton.setChangeListener(new FieldChangeListener() { public void fieldChanged(Field field, int context) { OnItemSelectedCallback callback = new OnItemSelectedCallback() { public void onItemSelected(String label) { TitleScreen.this.onItemSelected(label); } }; MyScreen myScreen = new MyScreen(callback); UiApplication.getUiApplication().pushScreen(myScreen); } }); add(myButton); } private void onItemSelected(String label) { // this will be called when a menu item is executed on the MyScreen // eg you can call smth like: myButton.setLabel(label); } } interface OnItemSelectedCallback { void onItemSelected(String label); } class MyScreen extends MainScreen { ObjectListField myList = new ObjectListField(); private final OnItemSelectedCallback onItemSelectedCallback; public MyScreen(OnItemSelectedCallback onItemSelectedCallback) { setTitle("Select an item below:"); this.onItemSelectedCallback = onItemSelectedCallback; myList.set(new String[] { "Item 1", "Item 2", "Item 3", "Item 4", }); add(myList); addMenuItem(myMenu); } private final MenuItem myMenu = new MenuItem("Select item", 0, 0) { public void run() { int index = myList.getSelectedIndex(); if (index < 0) return; String item = (String) myList.get(myList, index); Status.show("Selected: " + item); // TODO how to return to the previous screen here? // TODO how to call myButton.setLabel(item) here? // notify the parent screen onItemSelectedCallback.onItemSelected(item); // close the current screen UiApplication.getUiApplication().popScreen(MyScreen.this); } }; }