Question

我目前遇到WP7的TimePicker问题，特别是将其绑定到ViewModel。有问题的TimePicker设置警报的时间。首次加载页面时，TimePicker会正确显示Alarm对象的值（在这种情况下，默认值为12:00 am）。但是，当用户选择新值时，这不会反映在模型中 - 它会被先前的上午12:00覆盖。

我正在使用MVVM创建此表单并保存数据绑定。有什么特别的，我做错了吗？

（查看）AlarmEditorControl.xaml

<TextBlock Height="30" HorizontalAlignment="Left" Margin="1,6,0,0" Name="lblAlarmTime" Text="Alarm Time:" VerticalAlignment="Top" Grid.Column="2" FontSize="26" />
<!-- Data binding isn't working for updates! -->
<toolkit:TimePicker HorizontalAlignment="Left" Margin="140,34,0,0" Name="tpAlarmTime" VerticalAlignment="Top" Width="161" Grid.Column="1" Grid.ColumnSpan="2" Value="{Binding Path=Time, Mode=TwoWay}" />

（ViewModel）AlarmEditorModel.cs

[DataContractAttribute]
public class AlarmEditorModel
{
    private int _index;

    [DataMemberAttribute]
    public Alarm Alarm { get; set; }

    [DataMemberAttribute]
    public int Index
    {
        get
        {
            return _index;
        }

        set
        {
            _index = value;
        }
    }

    public AlarmEditorModel(int index)
    {
        _index = index;
        Alarm = new Alarm();

        // Get the list of alarms
        AlarmSerializer serializer = new AlarmSerializer();

        // Check the index is in range
        List<Alarm> alarms = serializer.AlarmList;
        if (_index > -1 && index < alarms.Count)
        {
            Alarm = alarms[_index];
        }
    }

    public void Commit()
    {
        // Get the current list of alarms
        AlarmSerializer serializer = new AlarmSerializer();
        List<Alarm> alarms = serializer.AlarmList;

        // Replace our new value
        alarms[_index] = Alarm;
        serializer.AlarmList = alarms;
    }
}

（型号）Alarm.cs

[DataContract]
public class Alarm : INotifyPropertyChanged
{
    private bool _active;
    private DateTime _time;

    [DataMember]
    public string Name { get; set; }

    [DataMember]
    public DateTime Time
    {
        get
        {
            return _time;
        }
        set
        {
            if (_time != value)
            {
                _time = value;
                RaisePropertyChanged("Time");
            }
        }
    }

    [DataMember]
    public AlarmFrequency Frequency { get; set; }

    [DataMember]
    public AlarmTone Tone { get; set; }

    [DataMember]
    public bool Active { 
        get {
            return _active;
        }
        set {
            _active = value;
        } 
    }

    public string AlarmTimeString { 
        get {
            return Time.ToShortTimeString();
        }
    }



    /**
     * Default Constructor
     */
    public Alarm()
    {
        Debug.WriteLine("Alarm: Using default constructor");
        this.Name = "New Alarm";
        this.Time = DateTime.Today;
        this.Frequency = new AlarmFrequency();
        this.Tone = new AlarmTone();
        this.Active = true;

        Debug.WriteLine("Alarm hours is " + this.Time.Hour);
    }

    /**
     * Parameterised constructor
     */
    public Alarm(string Name, DateTime Time, AlarmFrequency Frequency,
                    AlarmTone Tone, bool Active)
    {
        Debug.WriteLine("Alarm: Using parameterised constructor");
        this.Name = Name;
        this.Time = Time;
        this.Frequency = Frequency;
        this.Tone = Tone;
        this.Active = Active;
       }
}

（调用页面）NewAlarm.xaml.cs

 private List<Channel> feeds;
    private AlarmEditorModel _aem;
    private int _index;

    public NewAlarm()
    {
        InitializeComponent();

        feeds = new List<Channel>();
        feeds.Add(new Channel(null, null, "Feed 1", DateTime.Now));
        feeds.Add(new Channel(null, null, "Feed 2", DateTime.Now));
    }

    /**
     * Setup functions when the page is loaded
     */
    protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
    {
        // Function vars + debug

        Debug.WriteLine("Navigating to");

        // Check if we're recovering from tombstone
        if (!StateUtilities.IsLaunching && this.State.ContainsKey("AlarmState"))
        {
            // Recover the saved model
            _aem = (AlarmEditorModel)this.State["AlarmState"];
        }
        else 
        {
            try
            {
                // Editing an alarm.
                _index = Convert.ToInt32(this.NavigationContext.QueryString["index"]);
                Debug.WriteLine("Editing an alarm");
            }
            catch (KeyNotFoundException knfe)
            {
                Debug.WriteLine(knfe.Message);

                // No index provided, new alarm
                _index = -1;
            }

            // Set the model from the index
            _aem = new AlarmEditorModel(_index);
        }

        AlarmEditor.DataContext = _aem.Alarm;
        Debug.WriteLine(_aem.Alarm.Time.Hour);
    }

    /**
     * Preserve alarm details when tombstoning
     */
    protected override void OnNavigatedFrom(System.Windows.Navigation.NavigationEventArgs e)
    {
        base.OnNavigatedFrom(e);

        if (this.State.ContainsKey("AlarmState"))
        {
            this.State["AlarmState"] = _aem;
        }
        else
        {
            this.State.Add("AlarmState", _aem);
        }

        StateUtilities.IsLaunching = false;
    }

编辑1

看起来Alarm.Time的setter被调用两次。通过将以下调试行添加到Time属性：

[DataMember]
    public DateTime Time
    {
        get
        {
            return _time;
        }
        set
        {
            Debug.WriteLine("Current time is " + _time.ToShortTimeString());
            Debug.WriteLine("New time is " + value.ToShortTimeString());

            if (_time != value)
            {
                Debug.WriteLine("Changing time value");
                _time = value;
                RaisePropertyChanged("Time");
            }
        }
    }

将时间设置为上午9:10时，日志中会生成以下输出：

Current time is 4:00 AM
New time is 9:10 AM 
Changing time value
Current time is 12:00 AM 
New time is 4:00 AM 
Changing time value

Answer 1

我认为问题已经解决了。在从Tombstone恢复时，我需要在OnNavigatedTo中进行额外检查，以便在ViewModel覆盖之前获取TimePicker的值：

protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
        // Check if we're recovering from tombstone
        if (!StateUtilities.IsLaunching && this.State.ContainsKey("AlarmState"))
        {
            // Recover the saved model
            _aem = (AlarmEditorModel)this.State["AlarmState"];

            // Use the value from the TimePicker
            _aem.Alarm.Time = (DateTime)AlarmEditor.tpAlarmTime.Value;
        }
        else 
        ...

需要对此解决方案进行一些测试，但到目前为止它似乎正在完成这项工作。

WP7：TimePicker绑定不使用新值更新

1 个答案: