java - 变量无法解析

Question

我正在阅读 Beginning BlackBerry 7 Development 这本书，并真正将我很少或根本不存在的 oop/java 技能用于测试 - eclipse 从书中的代码中抛出一个错误，指出 loginhandler 尚未声明- 是的，它是正确的 - 它没有被宣布，但它也没有在书中被宣布。

已经完成的是一个名为 logincommandhandler 的内部类(在我的代码底部)，可以在此处的摘录中看到 - http://my.safaribooksonline.com/book/-/9781430230151/chapter-4-user-interface-basics/67 - 这就是调用的意思(我假设)但是我有限的 oop 技能我不知道 loginHandler 应该是什么 - 它应该用类型定义在某个地方吗？

(本书无勘误)

package com.beginningblackberry.uifun;

import net.rim.device.api.system.Bitmap;
import net.rim.device.api.ui.Field;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.component.BitmapField;
import net.rim.device.api.ui.container.MainScreen;
import net.rim.device.api.ui.container.HorizontalFieldManager;

import net.rim.device.api.ui.component.Dialog;
import net.rim.device.api.ui.component.EditField;
import net.rim.device.api.ui.component.PasswordEditField;
import net.rim.device.api.ui.component.SeparatorField;
import net.rim.device.api.ui.component.LabelField;

import net.rim.device.api.ui.component.CheckboxField;
import net.rim.device.api.ui.component.ObjectChoiceField;
import net.rim.device.api.ui.component.ButtonField;
import net.rim.device.api.ui.FieldChangeListener;

import net.rim.device.api.ui.component.Menu;
import net.rim.device.api.ui.MenuItem;
import net.rim.device.api.util.StringProvider;

import net.rim.device.api.command.Command;
import net.rim.device.api.command.CommandHandler;
import net.rim.device.api.command.ReadOnlyCommandMetadata;

public class UiFunMainScreen extends MainScreen implements FieldChangeListener {

    BitmapField img;
    EditField usernameField;
    PasswordEditField passwordField;
    ObjectChoiceField domainField;
    CheckboxField rememberCheckBox;
    ButtonField clearButton, loginButton;

    public UiFunMainScreen(){
        Bitmap logoBitmap = Bitmap.getBitmapResource("img/upd8rLOGO.png");


        img = new BitmapField(logoBitmap, Field.FIELD_HCENTER);     
        add(img);
        add(new SeparatorField());
        add(new LabelField("Please Enter Your Credentials:"));



        usernameField = new EditField("Username:","");
        passwordField = new PasswordEditField("Password:","");
        domainField = new ObjectChoiceField("Domain",new String[] {"Home","Work"});
        rememberCheckBox = new CheckboxField("Remember password",false);
        add(usernameField);add(passwordField);
        add(domainField);
        add(rememberCheckBox);

        add(new SeparatorField());
        clearButton = new ButtonField("Clear",ButtonField.CONSUME_CLICK);
        loginButton = new ButtonField("Login",ButtonField.CONSUME_CLICK);

        HorizontalFieldManager buttonManager = new HorizontalFieldManager(Field.FIELD_RIGHT);
        buttonManager.add(clearButton);
        buttonManager.add(loginButton);

        add(buttonManager);

        clearButton.setChangeListener(this);
        //loginButton.setChangeListener(this);
        loginButton.setCommand(new Command(LoginHandler));


    }
    //routing
    public void fieldChanged(Field field, int context){

        if(field == clearButton){
            clearTextFields();
        }else if(field == loginButton){
            login();
        }
    }


    private void login(){
        if(usernameField.getTextLength()== 0 || passwordField.getTextLength() == 0){
            Dialog.alert("You must enter a username and password");
        }
        else
        {
            String username = usernameField.getText();
            String selectedDomain = (String) domainField.getChoice(domainField.getSelectedIndex());
            LoginSuccessScreen loginSuccessScreen = new LoginSuccessScreen(username, selectedDomain);
            UiApplication.getUiApplication().pushScreen(loginSuccessScreen);
        }

    }
    public void clearTextFields ()
    {
        usernameField.setText("");
        passwordField.setText("");

    }
    protected void makeMenu(Menu menu, int instance){
        super.makeMenu(menu, instance);
        /*
        menu.add(new MenuItem(new StringProvider("Login"),20,10){

            public void run(){
                login();
            }   
        });
        */

        //login menu item       
        MenuItem loginMenu = new MenuItem(new StringProvider("Login"),20,10);
        loginMenu.setCommand(new Command(LoginHandler));
        menu.add(loginMenu);


        //clear text menu item
        menu.add(new MenuItem(new StringProvider("Clear"),20,10){
            public void run(){
                clearTextFields();
            }   
        });
    }

    class LoginCommandHandler extends CommandHandler
    {

        public void execute(ReadOnlyCommandMetadata metadata, Object context){
            login();
        }
    }


}

和错误-

LoginHandler cannot be resolved to a variable   UiFunMainScreen.java    /UiFun/src/com/beginningblackberry/uifun    line 69 Java Problem

有没有 blackberry/java 高手指出我哪里出错了？

更新

没有人真正回答这个问题 - 调用新的内部类，我改为调用它

MenuItem loginMenu = new MenuItem(new StringProvider("Login"),20,10);
loginMenu.setCommand(new Command(new LoginCommandHandler()));
menu.add(loginMenu);

更新 2 秒答案

将 loginHandler 声明为类变量也有效 -

LoginCommandHandler loginHandler = new LoginCommandHandler();

Answer 1

我的猜测是它应该是 LoginCommandHandler 的实例(最后声明的类)。这是一个猜测，但是一个有根据的猜测:Command 的构造函数需要一个 CommandHandler 实例，并且 LoginCommandHandler 扩展 CommandHandler , 所以...

最简单的改变是改变所有看起来像这样的地方:

loginButton.setCommand(new Command(LoginHandler));

到:

loginButton.setCommand(new Command(new LoginCommandHandler()));

例如，我们正在调用 LoginCommandHandler 构造函数并将生成的对象传递给 new Command()。

或者如果出于某种原因(我还没有真正阅读代码)您需要对处理程序的引用，声明并实例化它:

LoginCommandHandler loginHandler = new LoginCommandHandler();

...然后使用它

loginButton.setCommand(new Command(loginHandler));

(请注意，他们在引用的代码中有多个地方犯了这个错误。)