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88必发娱乐城2019-08-31 10:10
  1. Pictures time!

You have probably used theQTimerclass for basic timing operations in Qt. Common use cases include polling for events (not always a good approach, but sometimes necessary), updating the user interface or performing some other function at regular intervals. And you probably know about the repetitive and single-shot modes ofQTimertimers.

Author: Wish (Haotian Wei, born in 2002)


In this blog post we'll look at some of the other timer classes provided by Qt that you may not be familiar with if you've only use a simpleQTimer.

必发88手机版下载,Secrets lie through even just a nameless city in China. Our boy Wish just came back from an exam, and somehow he got involved, in the chaotic secret of an organization…

拍照比较标准的提法叫 take pictures, 所以你也可说, "Let's take a picture." 或是 "Let's get the picture taken." 然而小编个人相比较欣赏学老美口语的提法, "Pictures time!" 或是 "Photo time!" 你这样说老美就驾驭该照相了。

Before doing that, I'd like to point out a feature ofQTimeryou may not be aware of. Through thetimerTypeproperty, three different types of timers are supported:PreciseTimer,CoarseTimer, andVeryCoarseTimer. Each type offers different tradeoffs between accuracy and precision, overhead, and ease of use. You can read the details in the Qt documentation.


  1. Could you take a picture for me?

I should also mention that an alternative to using timers can be delays. While a busy wait is a well-knownanti-pattern, if can be appropriate in some cases, although usually not in an application's main or UI thread. Qt provides portable versions of a number of delay functions:msleep,qSleep,sleep, andusleep. Similar delay functions are part of the C++ standard library (for example,sleep_forandsleep_until), and the POSIX standard which most operating systems provide some level of conformance to.

"Quickly, we have to move! Grab that rifle on the table." Ethan shouted in a hurry as he looked away from his screens. Red flashes are all over the surveillance monitor, and the sound of the alarm is as loud as striking thunder.



TheQBasicTimerclass provides timer events for Qt objects. Compared toQTimer, it is a fast, lightweight, low-level class that is used internally by Qt.

To use the class you create aQBasicTimerinstance. The timer is started by calling itsstart()method specifying the timer repetition rate, timer type, and aQObject-derived object to receive the timer events.

When the timer times out, it sends a timer event to the object. It is a repetitive timer that will send timer events until itsstop()method is called.

I wrote a small example application that illustrates the use of aQBasicTimer. You can download the entire projecthere.

You can set the timer type from a combo box and start the timer by pressing theStartbutton. The elapsed time is shown on an LCD display widget. While the timer is running, theStartbuttons changes toStopso you can stop the timer. aClearbutton will reset the time to zero. A screen shot is shown below:

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Feel free to examine the code at your leisure. In the main window's constructor we create a timer instance:


When the Start button is pressed and the timer is stopped, we callstart()specifying the timer rate , timer type (taken from a combobox in the UI), and set the main window as the object to receive the timer events.

Timer events are received in thetimerEventmethod implemented in the class. We increment the timer count and update the LCD display. The event is also accepted, although that is not strictly necessary:

voidMainWindow::timerEvent(QTimerEvent*event){ count++; ui→lcdNumber→display(count/10.0); event→accept();}

You can experiment with the different timer types and see if the behavior changes. In most cases, including this application, it is usually more convenient to use aQTimerand connect itstimeout()signal to a slot.

For applications where you want the reduced overhead of aQBasicTimer(maybe one with many timers),QBasicTimercan be a good choice.

I picked up the SCAR on the table and loaded it at once. Ethan was loading another rifle while he was looking at the screen and noticed that someone exploding the front door of the hideout. "Bless my door! I'm gonna kill those..."

对于来United States纯旅游的人, "Could you take a picture for me?" 那句话是最实用的了, 其实比相当多老美相当的热情, 只要见到您把相机拿起来东张西望, 他们都会继续努力地问你需无需帮你照。有的时候候风景其实不如何, 不过盛情难却,只可以牺牲一下自家的底版了。


Another timer class provided by Qt isQElapsedTimer. Itis typically used to calculate the elapsed time between two events. The common use case is to create aQElapsedTimerinstance and call itsstart()method before performing a slow operation. Then, after the operation completes, calling the timer'selapsed()method will return the elapsed time in milliseconds. It provides a number of useful methods including returning the time remaining before a time periodor whether a certain amount of time has elapsed.

Common applications forQElapsedTimerinclude calculating the time of an operation and supporting a timeout if an operation takes too long to complete. I wrote aQElapsedTimerexample that illustrates some of the features of this timer type. A screen shot is shown below and the source code can be downloaded fromhere.

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The application allows you to select one of four operations, a floating point multiplication, division, sine, or cosine calculation, or no operation at all. You can also select how many times the operation will be performed. Clicking on theStartbutton will perform the operation the selected number of times, and then display information about how long it took.

The code is meant to illustrate how to use aQElapsedTimerand is not necessarily the best way to accurately measure these operations. In this case the timing is probably dominated by the random number generator function and not the actual operation being performed on the numbers.

Included in the code is an example of using thehasExpired()method to determine if a specific amount of time has passed. In the case of the multiply operation, it stops the operation if more than one second has elapsed.

Feel free to examine the code, and to test your understanding ofQElapsedTimerby making some changes. If you are familiar with C++11 or later, a possible enhancement would be to use C++ lambda functions to perform the operations.

Ethan didn't finish talking, and someone already kicked in the room. At that exact moment, I aimed down my rifle and pulled the trigger. With an exploding sound and a spark of light, the person suddenly fell on the ground.


有的时候 take a picture 也能够讲成, take a shot. 照相机喀擦一声就是三个shot,所以即使你要请人家帮你多照一张的话,就是 take one more shot. 举个例子,"Could you take one more shot for me from this angle?" (你能还是不能从那些角度再帮作者照一张啊?)


QDeadLineTimeris a class similar toQElapsedTimer, but is more convenient for calculating whether a specific future time has expired.

I didn't create an example application for this classes. It should be straightforward to modify theQElaspedTimerexample to use this class instead. For example, you could have the selected operation run repeatedly until a specified amount of time has passed.

Chapter 1 The Mysterious Man

  1. Take a picture, it lasts longer。

Other Related Classes

Qt has some other classes related to timers and timing. TheQTimerEventclass contains parameters that describe a timer event. In theQBasicTimerexample program, thedata passed to thetimerEvent()handler was aQTimerEventobject.

QMediaTimeRangeis part of the multimedia module and is used to represent time ranges.

TheQOpenGLTimerQueryclass wraps an OpenGL timer query object.

The rain is literally pouring down from the sky. But it wouldn't matter if I got an umbrella, right? The sound of the rain kept on beating on the umbrella and made weird noises, but it doesn't ruin my good mood. I have just finished one of the major tests in China - the Zhongkao, and I've graduated from middle school.


QML Types

In the QML world, Qt provides theTimerQML type. It provides similar functionality to theQTimerC++ class, offering repetitive or single shot timers that emit a signal at a specified rate.

Here is a standalone QML program that implements similar functionality to theQBasicTimerexample:a stopwatch application. It can be run from theqmlsceneprogram. Here is the complete source code:

// Simple QML Timer exampleimport QtQuick2.6import QtQuick.Controls2.4Rectangle{ height:200 width:250 propertyintcount:0 Timer{ id:timer interval:100 running:false repeat:true onTriggered:count+=1} Column{ anchors.fill:parent Text{ id:text font.pixelSize:100 text:.toFixed } Row{ spacing:10 Button{ text:timer.running?"Stop":"Start" onClicked:timer.running=!timer.running } Button{ text:"Reset" onClicked:count=0 } }}}

And here is a screen shot of the application running:

必发88手机版下载 5

"I'm home." I shouted to my mother while I entered the opened door of my small apartment. "Hello? Mom? Is anyone home?"

那句话实际有二种意思。 第一种是当你感到有些地点风景真的不错,非常值得回想的时候,能够如此说。但实际, 老美说那句话的时候常见都是另一种意思-- 请不要直接看本身! 记得有三遍作者看来贰个老美奇装异服,就多看了她两眼。他就对自己说, "Take a picture, it lasts longer." 后来本人才通晓, 那句话实际是在嘲弄自个儿,因为他意识自个儿在偷瞄他,所以她的意味正是说,“你乾脆照张相好了,那样能够保留比较久。。”


I think you can now appreciatethat Qt provides an extensive set of C++ classes to meetjust about any need related to timing, as well as a QMLTimertype. I should also mention that the C++ standard library also offers clock and timer functions, which canbe a viable approach depending on your requirements.

"Yes! Come here and meet Ethan, Wish!" My mother's voice came from the living room, and a mysterious man appeared right in front of me. Brown curly hair, woody brown eyes, tall and thin with a blue shirt, and a name tag is clipped on the front of the shirt, it reads: Ethan J. S. "You must be wish," the man had an American accent, "my name's Ethan James Shaffer. It's good to see you. I've just installed your Game Box, and if you would excuse me, I'm heading back to the HQ. Here's my card."

  1. Do you know how to do this timer thing?

Ethan looked through his pocket and handed me a paper card, it reads: