大约有 47,000 项符合查询结果（耗时：0.0651秒） [XML]
How to test if list element exists?
...es(foo) # TRUE
"b" %in% names(foo) # TRUE
"c" %in% names(foo) # FALSE
...and foo[["a"]] is safer than foo$a, since the latter uses partial matching and thus might also match a longer name:
x <- list(abc=4)
x$a # 4, since it partially matches abc
x[["a"]] # NULL, no match
[UPDATE] So, back t...
Running Python code in Vim
I am writing Python code using Vim, and every time I want to run my code, I type this inside Vim:
20 Answers
...
How to implement onBackPressed() in Fragments?
Is there a way in which we can implement onBackPressed() in Android Fragment similar to the way in which we implement in Android Activity?
...
What is the minimum valid JSON?
...a JSON text as being a serialized object or array.
This means that only {} and [] are valid, complete JSON strings in parsers and stringifiers which adhere to that standard.
However, the introduction of ECMA-404 changes that, and the updated advice can be read here. I've also written a blog post on ...
Master-master vs master-slave database architecture?
...
We're trading off availability, consistency and complexity. To address the last question first: Does this matter? Yes very much! The choices concerning how your data is to be managed is absolutely fundamental, and there's no "Best Practice" dodging the decisions. You n...
What does PHP keyword 'var' do?
...
It's for declaring class member variables in PHP4, and is no longer needed. It will work in PHP5, but will raise an E_STRICT warning in PHP from version 5.0.0 up to version 5.1.2, as of when it was deprecated. Since PHP 5.3, var has been un-deprecated and is a synonym for 'pu...
EF Code First: How do I see 'EntityValidationErrors' property from the nuget package console?
... putting a wrapper function in the Configuration class in the Seed method, and replaced calls to SaveChanges with calls to my function instead. This function would simply enumerate the errors within the EntityValidationErrors collection, and rethrow an exception where the Exception message lists th...
How do you crash a JVM?
...e JVM immediately without proper cleanup. But apart from that, native code and resource exhaustion are the most likely answers. Alternatively you can go looking on Sun's bug tracker for bugs in your version of the JVM, some of which allow for repeatable crash scenarios. We used to get semi-regular c...
How to know user has clicked “X” or the “Close” button?
... get it through the sender object. Try to cast sender as a Button control, and verify perhaps for its name "CloseButton", for instance.
private void Form1_FormClosing(object sender, FormClosingEventArgs e) {
if (string.Equals((sender as Button).Name, @"CloseButton"))
// Do something pro...
Spring schemaLocation fails when there is no internet connection
I am using Spring and in application-context.xml I have the following definitions:
18 Answers
...