我无法确定应用程序中if else语句的正确实现。目前我使用条件运算符&&和||进行比较，但是当我的应用程序在市场上启动时，我的代码没有按计划运行。基本上它应该工作的方式是，如果计数大于100并且应用程序仍然是试用许可证然后要求升级，否则如果计数小于或等于100并且应用程序仍然是试用许可证或应用程序是完整许可证，然后允许ApplyAndSaveAsync方法执行。
Settings.SavedCount.Value += 1;
if ((Settings.SavedCount.Value > 100) && (TrialViewModel.LicenseModeString == "Trial"))
{
MessageBoxResult result = MessageBox.Show("You have saved over 100 items! Would you like to continue?", "Congratulations", MessageBoxButton.OKCancel);
switch (result)
{
case MessageBoxResult.OK:
// A command takes a parameter and in this case we can pass null.
TrialViewModel.BuyCommand.Execute(null);
break;
case MessageBoxResult.Cancel:
return;
break;
}
}
else if (((Settings.SavedCount.Value <= 100) && (TrialViewModel.LicenseModeString == "Trial")) || (TrialViewModel.LicenseModeString == "Full"))
{
ApplyAndSaveAsync();
}
要注意，TrialViewModel.LicenseModeString在字符串比较中可以是Trial或Full，但它似乎正常工作。 Settings.SavedCount.Value也正常递增。 TrialViewModel.LicenseModeString查询应用程序中自动设置的许可证状态，无论用户是下载试用版还是完整版，或者用户将试用版升级到完整版，因此我认为这不是问题所在。出于某种原因，虽然在市场中以试用和完整状态测试我的应用程序时，ApplyAndSaveAsync方法永远不会执行？
我尝试撤消对TrialViewModel.LicenseModeString和Settings.Saved.Count.Value的检查，以便首先检查计数，但我不确定这是否会有所帮助。我引用了http://msdn.microsoft.com/en-us/library/aa691310(v=vs.71).aspx，其中指出The operation x && y corresponds to the operation x & y, except that y is evaluated only if x is true. The operation x || y corresponds to the operation x | y, except that y is evaluated only if x is false.所以我不确定下面的陈述是否会正常运作？
Settings.SavedCount.Value += 1;
if ((Settings.SavedCount.Value > 100) && (TrialViewModel.LicenseModeString == "Trial"))
{
//MessageBoxResult result = MessageBox.Show("You have saved over 100 filtered pictures! Would you like to continue?", "Congratulations", MessageBoxButton.OKCancel);
MessageBoxResult result = MessageBox.Show(AppResources.EditPage_MessageBoxContent_Purchase, AppResources.EditPage_MessageBoxCaption_Purchase, MessageBoxButton.OKCancel);
switch (result)
{
case MessageBoxResult.OK:
// A command takes a parameter and in this case we can pass null.
TrialViewModel.BuyCommand.Execute(null);
break;
case MessageBoxResult.Cancel:
if (editPagePivotControl != null && editPagePivotControl.SelectedIndex != 0)
{
//trialPopup.IsOpen = false;
editPagePivotControl.SelectedIndex = 0;
}
break;
}
}
else if (((Settings.SavedCount.Value <= 100) && (TrialViewModel.LicenseModeString == "Trial")) || (TrialViewModel.LicenseModeString == "Full"))
{
ApplySelectedEffectAndSaveAsync();
}
我的最后一个问题是，我应该使用单个&和|运算符吗？
Settings.SavedCount.Value += 1;
if ((Settings.SavedCount.Value > 1) & (TrialViewModel.LicenseModeString == "Trial"))
{
//MessageBoxResult result = MessageBox.Show("You have saved over 100 filtered pictures! Would you like to continue?", "Congratulations", MessageBoxButton.OKCancel);
MessageBoxResult result = MessageBox.Show(AppResources.EditPage_MessageBoxContent_Purchase, AppResources.EditPage_MessageBoxCaption_Purchase, MessageBoxButton.OKCancel);
switch (result)
{
case MessageBoxResult.OK:
// A command takes a parameter and in this case we can pass null.
TrialViewModel.BuyCommand.Execute(null);
break;
case MessageBoxResult.Cancel:
if (editPagePivotControl != null && editPagePivotControl.SelectedIndex != 0)
{
//trialPopup.IsOpen = false;
editPagePivotControl.SelectedIndex = 0;
}
break;
}
}
else if (((Settings.SavedCount.Value <= 1) & (TrialViewModel.LicenseModeString == "Trial")) | (TrialViewModel.LicenseModeString == "Full"))
{
ApplySelectedEffectAndSaveAsync();
}
TrialViewModel
#region fields
private RelayCommand buyCommand;
#endregion fields
#region constructors
public TrialViewModel()
{
// Subscribe to the helper class's static LicenseChanged event so that we can re-query its LicenseMode property when it changes.
TrialExperienceHelper.LicenseChanged += TrialExperienceHelper_LicenseChanged;
}
#endregion constructors
#region properties
/// <summary>
/// You can bind the Command property of a Button to BuyCommand. When the Button is clicked, BuyCommand will be
/// invoked. The Button will be enabled as long as BuyCommand can execute.
/// </summary>
public RelayCommand BuyCommand
{
get
{
if (this.buyCommand == null)
{
// The RelayCommand is constructed with two parameters - the action to perform on invocation,
// and the condition under which the command can execute. It's important to call RaiseCanExecuteChanged
// on a command whenever its can-execute condition might have changed. Here, we do that in the TrialExperienceHelper_LicenseChanged
// event handler.
this.buyCommand = new RelayCommand(
param => TrialExperienceHelper.Buy(),
param => TrialExperienceHelper.LicenseMode == TrialExperienceHelper.LicenseModes.Trial);
}
return this.buyCommand;
}
}
public string LicenseModeString
{
get
{
return TrialExperienceHelper.LicenseMode.ToString()/* + ' ' + AppResources.ModeString*/;
}
}
#endregion properties
#region event handlers
// Handle TrialExperienceHelper's LicenseChanged event by raising property changed notifications on the
// properties and commands that
internal void TrialExperienceHelper_LicenseChanged()
{
this.RaisePropertyChanged("LicenseModeString");
this.BuyCommand.RaiseCanExecuteChanged();
}
#endregion event handlers
TrialExperienceHelper.cs
#region enums
/// <summary>
/// The LicenseModes enumeration describes the mode of a license.
/// </summary>
public enum LicenseModes
{
Full,
MissingOrRevoked,
Trial
}
#endregion enums
#region fields
#if DEBUG
// Determines how a debug build behaves on launch. This field is set to LicenseModes.Full after simulating a purchase.
// Calling the Buy method (or navigating away from the app and back) will simulate a purchase.
internal static LicenseModes simulatedLicMode = LicenseModes.Trial;
#endif // DEBUG
private static bool isActiveCache;
private static bool isTrialCache;
#endregion fields
#region constructors
// The static constructor effectively initializes the cache of the state of the license when the app is launched. It also attaches
// a handler so that we can refresh the cache whenever the license has (potentially) changed.
static TrialExperienceHelper()
{
TrialExperienceHelper.RefreshCache();
PhoneApplicationService.Current.Activated += (object sender, ActivatedEventArgs e) => TrialExperienceHelper.
#if DEBUG
// In debug configuration, when the user returns to the application we will simulate a purchase.
OnSimulatedPurchase（）; #else // DEBUG //在发布配置中，当用户返回应用程序时，我们将刷新缓存。 RefreshCache（）; #endif // DEBUG } #endregion constructors
#region properties
/// <summary>
/// The LicenseMode property combines the active and trial states of the license into a single
/// enumerated value. In debug configuration, the simulated value is returned. In release configuration,
/// if the license is active then it is either trial or full. If the license is not active then
/// it is either missing or revoked.
/// </summary>
public static LicenseModes LicenseMode
{
get
{
#if DEBUG
return simulatedLicMode;
#else // DEBUG
if (TrialExperienceHelper.isActiveCache)
{
return TrialExperienceHelper.isTrialCache ? LicenseModes.Trial : LicenseModes.Full;
}
else // License is inactive.
{
return LicenseModes.MissingOrRevoked;
}
#endif // DEBUG
}
}
/// <summary>
/// The IsFull property provides a convenient way of checking whether the license is full or not.
/// </summary>
public static bool IsFull
{
get
{
return (TrialExperienceHelper.LicenseMode == LicenseModes.Full);
}
}
#endregion properties
#region methods
/// <summary>
/// The Buy method can be called when the license state is trial. the user is given the opportunity
/// to buy the app after which, in all configurations, the Activated event is raised, which we handle.
/// </summary>
public static void Buy()
{
MarketplaceDetailTask marketplaceDetailTask = new MarketplaceDetailTask();
marketplaceDetailTask.ContentType = MarketplaceContentType.Applications;
marketplaceDetailTask.Show();
}
/// <summary>
/// This method can be called at any time to refresh the values stored in the cache. We re-query the application object
/// for the current state of the license and cache the fresh values. We also raise the LicenseChanged event.
/// </summary>
public static void RefreshCache()
{
TrialExperienceHelper.isActiveCache = CurrentApp.LicenseInformation.IsActive;
TrialExperienceHelper.isTrialCache = CurrentApp.LicenseInformation.IsTrial;
TrialExperienceHelper.RaiseLicenseChanged();
}
private static void RaiseLicenseChanged()
{
if (TrialExperienceHelper.LicenseChanged != null)
{
TrialExperienceHelper.LicenseChanged();
}
}
#if DEBUG
private static void OnSimulatedPurchase()
{
TrialExperienceHelper.simulatedLicMode = LicenseModes.Full;
TrialExperienceHelper.RaiseLicenseChanged();
}
#endif // DEBUG
#endregion methods
#region events
/// <summary>
/// The static LicenseChanged event is raised whenever the value of the LicenseMode property has (potentially) changed.
/// </summary>
public static event LicenseChangedEventHandler LicenseChanged;
#endregion events
答案 0 :(得分：0)
你的逻辑似乎没问题。您确定TrialViewModel.LicenseModeString确切地返回Trial或Full吗？
顺便说一句，在您的情况下，使用&&或&运算符没有区别。当逻辑表达式的一部分是方法时，它确实有所不同。例如：
int i = 0;
if ((i >= 100) & (a.IncreaseCounter() > 5))
// a.IncreaseCounter() will be executed even while i is less than 100
if ((i >= 100) && (a.IncreaseCounter() > 5))
// a.IncreaseCounter() will not be excuted
第一个if语句首先计算表达式的两边，然后检查表达式是true还是false。第二个陈述使评估短路。因为左侧的表示是假的，所以它不会评估右侧，因为它已经知道最终结果将是假的。