demo | react-native redux 让开发者更好的使用redux | State Container library
kandi X-RAY | demo Summary
kandi X-RAY | demo Summary
安装依赖 npm install react-redux --save npm install redux-thunk --save npm install react-native-xtabbar --save npm install react-native-drawer-layout --save npm i react-native-elements --save npm i react-native-vector-icons --save && react-native link react-native-vector-icons npm install --save react-native-swipe-list-view. ##redux介绍 ####Provider 一个很简单的React组件,它主要的作用是把store放到context中,connect就可以获取store,使用store的方法,比如dispatch。其实没有被connect的组件通过声明contextTypes属性也是可以获取store,使用store的方法的,但是这个时候,如果使用dispatch修改了store的state,React-Redux并不能把修改后的state作为props给React组件,可能会导致UI和数据不同步,所以这个时候一定要清楚自己在做什么。 ####Connect 一个柯里化函数,函数将被调用两次。第一次是设置参数,第二次是组件与 Redux store 连接。connect 函数不会修改传入的 React 组件,返回的是一个新的已与 Redux store 连接的组件,而且你应该使用这个新组件。connect的使用方式是connect([mapStateToProps], [mapDispatchToProps], [mergeProps], [options])(Component),第一次调用的时候4个参数都是可选。 mapStateToProps在store发生改变的时候才会调用,然后把返回的结果作为组件的props。 mapDispatchToProps主要作用是弱化Redux在React组件中存在感,让在组件内部改变store的操作感觉就像是调用一个通过props传递进来的函数一样。一般会配合Redux的bindActionCreators使用。如果不指定这个函数,dispatch会注入到你的组件props中。 mergeProps用来指定mapStateToProps、mapDispatchToProps、ownProps(组件自身属性)的合并规则,合并的结果作为组件的props。如果要指定这个函数,建议不要太复杂。 options里面主要关注pure,如果你的组件仅依赖props和Redux的state,pure一定要为true,这样能够避免不必要的更新。 Component就是要被连接的React组件,组件可以是任意的,不一定是AppRoot。一般会是需要更新store、或者是依赖store中state的最小组件。因为被连接的组件在Redux的state改变后会更新,大范围的更新对性能不友好,而且其中有些组件可能是没必要更新也会更新,所以要尽量拆分、细化,connect仅仅要更新store或依赖store的state的最小组件。 ####Reselect mapStateToProps也被叫做selector,在store发生变化的时候就会被调用,而不管是不是selector关心的数据发生改变它都会被调用,所以如果selector计算量非常大,每次更新都重新计算可能会带来性能问题。Reselect能帮你省去这些没必要的重新计算。 Reselect 提供 createSelector 函数来创建可记忆的 selector。createSelector 接收一个 input-selectors 数组和一个转换函数作为参数。如果 state tree 的改变会引起 input-selector 值变化,那么 selector 会调用转换函数,传入 input-selectors 作为参数,并返回结果。如果 input-selectors 的值和前一次的一样,它将会直接返回前一次计算的数据,而不会再调用一次转换函数。这样就可以避免不必要的计算,为性能带来提升。 ####文件目录介绍 src ------------------------------------redux开发目录. redux的核心概念就是store、action、reducer,从调用关系来看如下所示 store.dispatch(action) --> reducer(state, action) --> final state. {type:'add_todo', text:'读书'} {type:'add_todo', text:'写作'} {type:'add_todo', text:'睡觉', time:'晚上'}. 3.reducer:一个普通的函数,用来修改store的状态。传入两个参数 state、action。其中,state为当前的状态(可通过store.getState()获得),而action为当前触发的行为(通过store.dispatch(action)调用触发)。reducer(state, action) 返回的值,就是store最新的state值。. // reducer方法, 传入的参数有两个 // state: 当前的state // action: 当前触发的行为, {type: 'xx'} // 返回值: 新的state var reducer = function(state, action){ switch (action.type) { case 'add_todo': return state.concat(action.text); default: return state; } };. redux-thunk 是一个比较流行的redux异步action中间件,比如action中有setTimeout或者通过fetch通用远程API这些场景,那么就应该使用redux-thunk了 redux-thunk 帮助你统一了异步和同步 action 的调用方式,把异步过程放在 action 级别解决.
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QUESTION
I have prepare 2 tree view in separate iframe using jstree. The right tree view should control the left tree view. When user click one one the list in right tree view, the respective item folder will open and selected on left tree view. I can make it happen using div in single page. I control the left tree view using instance of left tree view in right jstree div var instance = $('#left').jstree(true);
.
ANSWER
Answered 2021-Jun-16 at 03:07I had used document.getElementById('1').contentWindow.jQuery('#left').jstree(true);
to get instance from iframe with id='1'. In order to listen to right iframe(with id='2') if any menu has been clicked, I used document.getElementById('2').contentWindow.jQuery('#right').on("changed.jstree",function(e,data){})
. I get the instance of left iframe within this function. By using this instance, I has deselect previous selection, select current selection, and open children of selected menu.
index-12.html
QUESTION
I wrote a demo with some inline assembly (showing how to shift an array of memory right one bit) and it compiles and functions fine in GCC. However, the with Clang, I'm not sure if it's generating bad code or what but it's unhappy that I'm using memory despite the "rm" constraint.
I've tried many compilers and versions via Godbolt and while it works on all x86/x86_64 versions of GCC, it fails with all versions of Clang. I'm unsure if the problem is my code or if I found a compiler bug.
Code:
...ANSWER
Answered 2021-Jun-16 at 00:48I'm unsure if the problem is my code or if I found a compiler bug.
The problem is your code. In GNU assembler, parentheses are used to dereference like unary *
is in C, and you can only dereference a register, not memory. As such, writing 12(%0)
in the assembly when %0
might be memory is wrong. It only happens to work in GCC because GCC chooses to use a register for "rm"
there, while Clang chooses to use memory. You should use "r" (bytes)
instead.
Also, you need to tell the compiler that your assembly is going to modify the array, either with a memory
clobber or by adding *(unsigned char (*)[16])bytes
as an output. Right now, it's allowed to optimize your printf
to just hardcode what the values were at the beginning of the program.
Fixed code:
QUESTION
I have the following two interfaces, one which allows a nullable vin
, the other that doesn't:
ANSWER
Answered 2021-Jun-15 at 18:49You can use a type predicate to define a user-defined type guard like this:
QUESTION
We have thousands of structured filenames stored in our database, and unfortunately many hundreds have been manually altered to names that do not follow our naming convention. Using regex, I'm trying to match the correct file names in order to identify all the misnamed ones. The files are all relative to a meeting agenda, and use the date, meeting type, Agenda Item#, and description in the name.
Our naming convention is yyyymmdd_aa[_bbb]_ccccc.pdf
where:
- yyyymmdd is a date (and may optionally use underscores such as yyyy_mm_dd)
- aa is a 2-3 character Meeting Type code
- bbb is an optional Agenda Item
- ccccc is a freeform variable length description of the file (alphanumeric only)
Example filenames:
...ANSWER
Answered 2021-Jun-15 at 17:46The optional identifier ?
is for the last thing, either a characters or group. So the expression ([a-z0-9]{1,3})_?
makes the underscore optional, but not the preceding group. The solution is to move the underscore into the parenthesis.
QUESTION
I've been experimenting with the Kotlin coroutines in android. I used the following code trying to understand the behavior of it:
...ANSWER
Answered 2021-Jun-15 at 14:51This is exactly the reason why coroutines were invented and how they differ from threaded concurrency. Coroutines don't block, but suspend (well, they can do both). And "suspend" isn't just another name for "block". When they suspend (e.g. by invoking join()
), they effectively free the thread that runs them, so it can do something else somewhere else. And yes, it sounds like something that is technically impossible, because we are in the middle of executing the code of some function and we have to wait there, but well... welcome to coroutines :-)
You can think of it as the function is being cut into two parts: before join()
and after it. First part schedules the background operation and immediately returns. When background operation finishes, it schedules the second part on the main thread. This is not how coroutines works internally (functions aren't really cut, they create continuations), but this is how you can easily imagine them working if you are familiar with executors or event loops.
delay()
is also a suspending function, so it frees the thread running it and schedules execution of the code below it after a specified duration.
QUESTION
I am writing a program in C language using gtk3 library. I want it to be able to receive a h264 video stream from a certain IP address (localhost) and UDP/RTP PORT (5000).
In order to do it, I am using gstreamer to both stream and receive the video.
I managed to stream the video using the following pipeline :
send.sh :
gst-launch-1.0 filesrc location=sample-mp4-file.mp4 ! decodebin ! x264enc ! 'video/x-h264, stream-format=(string)byte-stream' ! h264parse ! rtph264p
I managed to display the video in a new window using the following pipeline :
receive.sh :
gst-launch-1.0 udpsrc port=5000 caps="application/x-rtp,encoding-name=H264" ! rtph264depay ! decodebin ! videoconvert ! autovideosink
At this point, everything works fine. But now I want to receive the stream and display it inside my C/GTK program. I am using the following code (found on internet and adapted to make it compile) :
...ANSWER
Answered 2021-Jun-15 at 11:39Here is the solution I found :
Changin xvimagesink by ximagesink :
sink = gst_element_factory_make ("xvimagesink", NULL); g_assert(sink);
becomes
sink = gst_element_factory_make ("ximagesink", NULL); g_assert(sink);
Hope it will help some of you facing the same problem.
QUESTION
Traceback (most recent call last):
File "", line 335, in
+ my_value_a
TypeError: can only concatenate str (not "NoneType") to str
...ANSWER
Answered 2021-Jun-15 at 11:26So if the key for os.getenv()
is invalid, it returns the default values that you pass as the second parameter. If you don't set this default value, it returns a None
. Possible Fixes:
QUESTION
I can't do something so simple and I'm pissed off. I am using bootstrap in Laravel. I need to set it up for mobile. The footer either hovers over the body or stays in the middle of the page. How can I solve this?
...ANSWER
Answered 2021-Jun-15 at 10:44I had the same issue with fixed footer at bottom and its mainly due to html structure. This post has well explained fixed bottom footer
QUESTION
In this minimal example, I'm adding a THREE.SphereGeometry to a THREE.Group and then adding the group to the scene. Once I've rendered the scene, I want to remove the group from the scene & dispose of the geometry.
...ANSWER
Answered 2021-Jun-15 at 10:37Ideally, your cleanup should look like this:
QUESTION
I wanted to build a very simple demo. A button which you can click, and it counts the clicks.
Code looks like this:
...ANSWER
Answered 2021-Jun-09 at 08:12You need to use the "remember" keyword for the recomposition to happen each time, as explained here: https://foso.github.io/Jetpack-Compose-Playground/general/state/
In short, your composable would look like this:
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