components | 易学教程

Checking for Undefined In React

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问题 I have a scenario where I'm passing data from a reducer into my react state. data: { "id": 1, "title": "Test", "content": { "body": "sdfsdf" "image": "http://example.com" } } Using componentWillRecieveProps, this works perfectly for retrieving the title. componentWillReceiveProps(nextProps) { this.setState({ title: nextProps.blog.title, }) } However, I'm having difficulty retrieving the nested fields. When I do this: componentWillReceiveProps(nextProps) { console.log("new title is", nextProps

How to render a list of static content with Vue named slot?

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问题 I have trouble figuring out how to get the following to work: My parent template <comp> <a href="#" slot="links>link 1</a> <a href="#" slot="links>link 2</a> </comp> and my component comp template looks like the following: <ul class="comp"> <li class="comp-item"><slot name="links"></slot></li> </ul> currently all my anchors goes to that single li tag (which is expected) but I would like to be able to produce multiple li for every named slot I inserted like the following: <ul class="comp"> <li

Update a default value only during design-time

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问题 I would like to update the default value of a private variable linked to a public property only during design-time, in case it's possible. TMyComp = class(TComponent) private FColumnWidth: Integer; FColumnWidthDef: Integer; protected public constructor Create(AOwner: TComponent); override; destructor Destroy; override; published property ColumnWidth: Integer read FColumnWidth write SetColumnWidth default 50; end; ... constructor TMyComponent.Create(AOwner: TComponent); begin inherited;

AngularJS - Run function of child controller from parent controller

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问题 I have read many questions on this but still can't find solution that will be clean and reusable enough. What I tried and don't want to use: Events - $emit and $broadcast, DOM manipulation - for example angular.element('nameOfElement').scope() to access scope of child, $onChange in child component Simple example I've build simplified scenario of to present the problem. On page there is TimerComponent that shows minutes and seconds. It have controller TimerController to change its state: start

Passing nil as a parameter in place of a TComponent

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问题 I've come across some code that's throwing an exception (EIntfCasterror Cast not supported) when it passes nil to a constructor expecting a TComponent, like so: obj := SomeClass.Create(nil); The unit this is in does not contain a form and even TForm requires a TComponent be passed to it when you call its constructor. What should I pass in place of nil if anything exists or is there a way to get it to accept nil. Thank you. Also, I don't have the source code which calls the method this is in,

Issue passing value into Angular 2 component [duplicate]

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问题 This question already has answers here : Angular 2 external inputs (4 answers) Closed 3 years ago . I am trying to pass a simple string into an angular 2 component. For the life of me I can't find the issue. I am passing the value in as a hardcoded value on the component from index.html <html> <head> <title>Angular 2 QuickStart</title> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <link rel="stylesheet" href="styles.css"> <!-- 1. Load libraries --

Java Layout not showing components (sometimes)

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问题 I'm writing a MathQuiz for my pupils including JLatexMath for rendering and jinput for the buzzers. The problem is, that sometimes (like every fourth time) when I start the program, none of the components are visible. They appear after resizing the JFrame. First I was thinking of Bugs in the jinput or jlatexMath libraries, but I do get the same Error even with this minimal Code: public class Shell extends JFrame{ private JButton button1; private JButton button2; private Formula formula;

Helper Function with argument called before component mount in React Native

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问题 I'm testing that my express server is running in React Native by calling a simple helper function in my component. This is the helper function: //Helper functions testFetch(msg) { console.log("Msg: ", msg); fetch("http://localhost:5000", { method: "GET", headers: { Accept: "application/json", "Content-Type": "application/json" } }) .then(response => response.json()) .then(responseJson => { console.log("Express response: ", responseJson); this.setState({ myText: responseJson }); }) .catch

Image editor component for use in WPF rich client application

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问题 Do you know of a simple .NET component which can be used in a WPF client application with these features: load images from file or clipboard into canvas, scaling and moving, define canvas background color, export canvas as new image. Thx in advance, Prensen 回答1: What about theese? http://xdraw.codeplex.com/ 回答2: http://www.codeproject.com/KB/WPF/WPF_DrawTools.aspx 来源： https://stackoverflow.com/questions/537007/image-editor-component-for-use-in-wpf-rich-client-application

How to draw on a TPanel

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问题 I need to draw on a TPanel, ideally directly so I don't have another component on top of it getting in the way of mousevent-event trapping (I want to draw a little "size-grip" on it). How should I go about doing this? 回答1: To really do it right, you should probably write a descendant class. Override the Paint method to draw the sizing grip, and override the MouseDown , MouseUp , and MouseMove methods to add resizing functionality to the control. I think that's a better solution than trying to