无法使用简单的Action
根据我正在阅读的内容，我应该能够注册一个Action类型的委托来取消执行，但编译器给我和错误说明：'DisplayMessage'委托不能在当前上下文中使用。 我不知道我做错了什么。 这里是代码在该地区评论，我得到的错误...
我更新了代码，而Console.Writeline正常工作时，调用消息框方法给了我一个错误，说明无法从方法组转换为Action委托。 这里是更新后的代码：
编辑：我之后的最后一个功能是调用一个实际的方法，可能与Action的签名略有不同。 以下修改类型的作品，除了两次打印窗口。 我不明白为什么它会这样做，因为我正在复制代码中相关Console.WriteLine行的每一行。 我意识到我写的方法和Register方法接受的是Action之间的类型不匹配。 现在，我基本上试图弄清楚当方法签名相同时，我得到两个MessageBox，并且代码是相同的。
感谢大家的反馈。 以下代码以我想要的方式工作。 这是评论，我张贴它，以防其他人喜欢做类似的事情。
using System; using System.Threading; using System.Windows.Forms; namespace CancellationSource { internal delegate void DisplayMessage(string message); internal static class Program { static void Main(string[] args) { CancellationTokenSource cts = new CancellationTokenSource(); ThreadPool.QueueUserWorkItem(o => Count(cts.Token, 50)); //ThreadPool.QueueUserWorkItem(o => Count(CancellationToken.None, 50)); Console.WriteLine("Press <enter> to cancel the operation."); Console.ReadLine(); Action<Object> messageTarget; messageTarget = Console.WriteLine; cts.Token.Register(Console.WriteLine, null, true); messageTarget = ShowWindowsMessage; messageTarget ("This should print in box"); //This code opens a //Message box only when the called thread operation is cancelled. This code calls two different methods //of type Action<Object> when the spawned / requested thread is canceled. //cts.Token.Register(messageTarget, null, true); cts.Cancel(); Console.ReadLine(); } //Notice in order to get the method below to execute upon thread cancelation, I had to make sure its //its signature is one of Action<Object> private static void ShowWindowsMessage(object value) { var message = (string)value; MessageBox.Show(message); } private static void Count(CancellationToken token, Int32 countTo) { for (int count = 0; count < countTo; count++) { if (token.IsCancellationRequested) { Console.WriteLine("Count is cancelled"); break; } Console.WriteLine(count); Thread.Sleep(200); } Console.WriteLine("Count is done"); } } }According to the content I am reading, I should be able to register a delegate of type Action to be executed upon cancelation, but the complier gives me and error stating: 'DisplayMessage' delegate can not be used in the current context. I can not tell what I am doing wrong. Here is the code commented in the area, which I get the error...
I updated the code, and while Console.Writeline works, calling a message box method gives me an error stating can not convert from method group to Action delegate. Here is the updated code:
edit: The last functionality I was after was to call an actual method, one that perhaps has slightly different signature from Action. The following modification kind of works, except it prints the Window twice. I do not get why it is doing that since I am copying every line from the relevant Console.WriteLine lines in my code. I realized that I had a type mismatch between the method I wrote and what Register method accepts which is Action. Now I am basically trying to figure out what I get two MessageBoxs when the method signatures are the same, and the code is the same.
Thank you for everyone's feedback. The following code works the way I wanted. It is commented, and I am posting it in case someone else likes to do something similar.
using System; using System.Threading; using System.Windows.Forms; namespace CancellationSource { internal delegate void DisplayMessage(string message); internal static class Program { static void Main(string[] args) { CancellationTokenSource cts = new CancellationTokenSource(); ThreadPool.QueueUserWorkItem(o => Count(cts.Token, 50)); //ThreadPool.QueueUserWorkItem(o => Count(CancellationToken.None, 50)); Console.WriteLine("Press <enter> to cancel the operation."); Console.ReadLine(); Action<Object> messageTarget; messageTarget = Console.WriteLine; cts.Token.Register(Console.WriteLine, null, true); messageTarget = ShowWindowsMessage; messageTarget ("This should print in box"); //This code opens a //Message box only when the called thread operation is cancelled. This code calls two different methods //of type Action<Object> when the spawned / requested thread is canceled. //cts.Token.Register(messageTarget, null, true); cts.Cancel(); Console.ReadLine(); } //Notice in order to get the method below to execute upon thread cancelation, I had to make sure its //its signature is one of Action<Object> private static void ShowWindowsMessage(object value) { var message = (string)value; MessageBox.Show(message); } private static void Count(CancellationToken token, Int32 countTo) { for (int count = 0; count < countTo; count++) { if (token.IsCancellationRequested) { Console.WriteLine("Count is cancelled"); break; } Console.WriteLine(count); Thread.Sleep(200); } Console.WriteLine("Count is done"); } } }
原文：https://stackoverflow.com/questions/40721590
最满意答案
为了节省一点点的内存/时间，你可以像这样修改@Ben Bolker的解决方案：
datlist <- lapply(csvnames,read.csv, colClasses=c("character", "NULL")) rowseq <- seq_len( max(vapply(datlist,nrow, integer(1))) ) keylist <- lapply(datlist,function(x) { x[[1]][rowseq] ) }) names(keylist) <- paste(KEYTERMS,csvnames,sep="_") #do.call(cbind,keylist) do.call(data.frame,keylist)...我只是改变了，只有第一列被读取，并且通过观察选择延伸到字符矢量焊盘之外的序列自动地用NA来简化NA填充。
如果你保持旧的填充方式，至少应该使用
NA_character_而不是NA来避免不必要的强制。我还通过数字而不是名称来索引
KEYTERMS列（因为应该只有一个）。 我也将sapply改为sapply，因为我更喜欢它:) - 它实际上也更快。最后你说你想要一个
data.frame。 最后一行产生的不是矩阵。To save a LITTLE memory/time you could modify the solution from @Ben Bolker like this:
datlist <- lapply(csvnames,read.csv, colClasses=c("character", "NULL")) rowseq <- seq_len( max(vapply(datlist,nrow, integer(1))) ) keylist <- lapply(datlist,function(x) { x[[1]][rowseq] ) }) names(keylist) <- paste(KEYTERMS,csvnames,sep="_") #do.call(cbind,keylist) do.call(data.frame,keylist)...I just changed so that only the first column is read, and simplified the NA padding by observing that selecting a sequence that extends outside a character vector pads with NA automatically...
If you kept the old way of padding, you should at least pad with
NA_character_instead ofNAto avoid unnecessary coercion.I also index the
KEYTERMScolumn by number instead of name (since there should be only one). I also changedsapplytovapplybecause I like it better :) - it actually is faster too.Finally you said you wanted a
data.frame. The last line produces that instead of a matrix.
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