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MQTT物联网协议完全实践指南 · App Inventor 2 中文网
...态处理
when UrsPahoMqttClient1.ConnectionStateChanged newState
do
if newState = 1 then // 连接成功
set CurrentRetry to 0
set Label_ConnectionStatus.Text to "已连接 - 在线"
set Label_ConnectionStatus.TextColor to Green
call subscribeToAllTopics
...
How can I avoid running ActiveRecord callbacks?
...n :do_something_else
skip_callback :validation, :before, :do_something, if: :skip_some_callbacks
skip_callback :validation, :after, :do_something_else, if: :skip_some_callbacks
end
person = Person.new(person_params)
person.skip_some_callbacks = true
person.save
...
How do I set up a simple delegate to communicate between two view controllers?
.../ See http://stackoverflow.com/a/4796131/263871 for the rationale
// (Tip: If you're not using ARC, use `assign` instead of `weak`)
@property (nonatomic, weak) id<ChildViewControllerDelegate> delegate;
// A simple IBAction method that I'll associate with a close button in
// the UI. We'll cal...
How to find third or nth maximum salary from salary table?
...
Use ROW_NUMBER(if you want a single) or DENSE_RANK(for all related rows):
WITH CTE AS
(
SELECT EmpID, EmpName, EmpSalary,
RN = ROW_NUMBER() OVER (ORDER BY EmpSalary DESC)
FROM dbo.Salary
)
SELECT EmpID, EmpName, EmpSalar...
Given two directory trees, how can I find out which files differ by content?
If I want find the differences between two directory trees, I usually just execute:
10 Answers
...
OS X: equivalent of Linux's wget
...ng third-party software is not an option, for this has to run on a lot of different systems which I don't have control on).
...
How can I read a large text file line by line using Java?
...null) {
// process the line.
}
}
You can read the data faster if you assume there is no character encoding. e.g. ASCII-7 but it won't make much difference. It is highly likely that what you do with the data will take much longer.
EDIT: A less common pattern to use which avoids the sco...
How do I handle too long index names in a Ruby on Rails ActiveRecord migration?
...id", "subject_type_id"],
:unique => true,
:name => 'my_index'
If using the :index option on references in a create_table block, it takes the same options hash as add_index as its value:
t.references :long_name, index: { name: :my_index }
...
Why is there extra padding at the top of my UITableView with style UITableViewStyleGrouped in iOS7
... Although this "brute force" solution works, I think the bottom ones (specifically the automatically adjust insets) should be ranked higher.
– eladleb
Apr 2 '14 at 13:37
...
Force R not to use exponential notation (e.g. e+10)?
... methods listen to some options. Including 'scipen' -- a penalty for scientific display. From help(options):
‘scipen’: integer. A penalty to be applied when deciding to print
numeric values in fixed or exponential notation. Positive
values bias towards fixed and ne...