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AppInventor2有没有删除撤销功能？ - App应用开发 - 清泛IT社区，为创新赋能！
...能。代码（逻辑）设计视图，可以使用 Ctrl+Z 撤销，Ctrl+Y 反撤销。
界面设计没有撤销功能，有时不小心删除了组件，真的就没法恢复了，有时真的有些不太方便。
不过不用着急，中文网已经推出了“复制屏幕”功能，可以...
How do you do a deep copy of an object in .NET? [duplicate]
I want a true deep copy. In Java, this was easy, but how do you do it in C#?
11 Answers
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Get the first element of each tuple in a list in Python [duplicate]
An SQL query gives me a list of tuples, like this:
5 Answers
5
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What is the difference between active and passive FTP?
...passive are the two modes that FTP can run in.
For background, FTP actually uses two channels between client and server, the command and data channels, which are actually separate TCP connections.
The command channel is for commands and responses while the data channel is for actually transferring...
How to convert an array of strings to an array of floats in numpy?
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Well, if you're reading the data in as a list, just do np.array(map(float, list_of_strings)) (or equivalently, use a list comprehension). (In Python 3, you'll need to call list on the map return value if you use map, since map returns...
What is the 'dynamic' type in C# 4.0 used for?
C# 4.0 introduced a new type called 'dynamic'. It all sounds good, but what would a programmer use it for?
10 Answers
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How do I make a list of data frames?
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This isn't related to your question, but you want to use = and not <- within the function call. If you use <-, you'll end up creating variables y1 and y2 in whatever environment you're working in:
d1 <- data.frame(y1 <- c(1, 2, 3), y2...
How do I disable form resizing for users? [duplicate]
How do I disable form resizing for users? Which property is used?
7 Answers
7
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Why is it bad practice to call System.gc()?
...er answering a question about how to force-free objects in Java (the guy was clearing a 1.5GB HashMap) with System.gc() , I was told it's bad practice to call System.gc() manually, but the comments were not entirely convincing. In addition, no one seemed to dare to upvote, nor downvote my ans...
How to parse/format dates with LocalDateTime? (Java 8)
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Parsing date and time
To create a LocalDateTime object from a string you can use the static LocalDateTime.parse() method. It takes a string and a DateTimeFormatter as parameter. The DateTimeFormatter is used to specify the date/time pattern.
String str = "1986-04-08 12:30";
DateTimeFormatter ...