黑莓手机：选择列表中的项目，返回previous屏幕 [英] Blackberry: select item in a list, return to previous screen

问题描述

我有prepared很短的测试案例（S。下文）我的问题。

I have prepared a very short test case (s. below) for my question.

在点击一个按钮，我想在一个新的屏幕可显示的字符串列表。

On a button click I would like to display a list of strings in a new screen.

在用户选择列表中的一个项目后，previous屏幕应该再次显示和按钮标签应设置为选定的字符串。

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 string.

我的2个问题是：

1. 从菜单里面，我不知道如何弹出当前显示的屏幕


2. 如何选择的项目从一个屏幕传递到另一个（假设我不想前者屏幕上引入一个公共变量/方法作为一种解决方法）

请建议进行必要的更改我的的src \\ mypackage中\\ MyList.java

Please suggest 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?
        }
    };
}

感谢您！
亚历克斯

Thank you! Alex

推荐答案

使用一个回调格局：

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
        // e.g. 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);
        }
    };
}

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