Struggling with some basic react-native stuff.
I have a master-detail scenario.
I push an edit button on a list-item to get to a detail-view, in that view I add a save-button to a navigation bar. Plain and simple.
Navigation to the detail-screen is done by:
this.props.navigator.push({
component: EditScreen,
passProps: {
id:myID,
},
onPress: this.onSave,
rightText: 'Save'
});
}
When tapping the save-button on the navigationbar, the onSave method of the parent component is called missing some context of the modifications.
How is this done in react-native?
I'm a react-native beginner, just want a clear view on how this stuff happens before moving to some flux-inspired libs ;-)
Update - Bind to this is not the problem
Flow:
I press a row which triggers an onEdit method passing in the ID of
the item i want to edit
onEdit pushes the EditScreen component on the navigator
onEdit adds the rightText and onPress bound to this (onSave is bound in the constructor as stated by some comments/answers)
When navigating to the EditScreen, the entity is fetched by its id
I edit the entity and press 'Save'
When pressing save, I return to the parent view and have no reference to the entity. That's my problem, not the binding of the method.
When using es6 classes, this is not automatically bound to the function, like React.createClass did. You have to manually bind this to the class functions. There are multiple ways of doing this.
You can use es6 fat arrows to bind this:
onPress: () => this.onSave()
You can use Function.prototype.bind():
onPress: this.onSave.bind(this)
You can also bind them on the constructor, so the method is created only once (most performant way, but won't matter very much if you are just building regular UI; if your onSave function is being called 1000 times per frame, then this might be a good idea):
constructor () {
super()
this.onSave = this.onSave.bind(this)
}
Related
I have a quite decent background in android but now I am starting digging into react native and I am really confused with the ways to change the state of a component through hooks and set state function.
To the point, I have my main screen and I have many small components which change visibility. This is done by letting the user change some filter settings within dialogs. So the suggested way to do that is by having a hook in my main screen with a list that holds the values for the visibility of each component. But since I change the visibility of the components from inside the modals, every time I want to show a modal I will have to pass in a different function(for example setComponentEnable or setComponentDisabled) to set the state for each component. So my main screen will be polluted from all these small functions. Also I should not forget to mention that my modals are consisted from many smaller components and I will have to pass as deep as it goes the proper function to match the user action.
So my question is, is there a way to do this thing without polluting my main with all these small functions and make it possible for the main screen to update every time the user change the filters within the modals?
I already read about context but the docs say:
Context is designed to share data that can be considered “global” for a tree of React components, such as the current authenticated user, theme, or preferred language.
So I dont think that this should be a great case for context use.
What I am trying to do now is create a hook with a list
const [isibility, setVisibility] = useState([]);
create visibility handler functions
const setVisibilityEnable = () => {
...
}
and pass it into my modal.
<MyModal
visibilityHandler={setVisibilityEnable}/>
Is there a way to manipulate the state without passing all these callbacks to the modals? Or maybe is there anyone that can suggest a better and clean solution to avoid end up having a really huge main screen?
you can include all the settings in one object and pass that object to all the components. Then each component will then modify that object accordingly.
const defaultVisibility = {
childComponentOne: true,
childComponentTwo: true,
};
const [visibilityObject, setVisibilityObject] = useState(defaultVisibility);
pass both the function and the object into your child components:
<ChildComponentOne visibilityObject={visibilityObject} setVisibilityObject={setVisibilityObject} />
Then in your child component, you set the visibility like so:
setVisibilityObject({...visibilityObject, childComponentOne: false});
Why you don't just pass a property to your modal and check if changed in oncomponentdidchange method?
componentDidUpdate(prevProps) {
if (this.props.yourPoperty!== prevProps.yourPoperty) {
//do your visibility stuff
}
}
Alternatively you can do it with redux when you connect your components to the store.
First, let me say that the v-navigation-drawer works as intended, i.e.:
On clicking the hamburger menu the TOGGLE_DRAWER mutation is committed, and it toggles open/closed, updating the state.
On window resize it opens/closes at a designated breakpoint
So it works.
BUT the window resize does not properly toggle the mutation and I keep getting a Vuex mutation error when I resize the window:
I understand why I'm getting this error - the $store.state.ui.drawer is being modified outside of the mutator (it's the v-navigation-drawer's v-model):
<v-navigation-drawer
v-model="$store.state.ui.drawer"
app
clipped
>
I get it's bad form to bind the state to the v-model. But when I try to make a drawer computed property with a get() and set() method that properly gets/commits a mutation, the browser crashes (presumably because the set method triggers an endless loop of commits toggling drawer true/false into infinity):
computed: {
drawer: {
get () {
return this.$store.state.ui.drawer
},
set () {
this.$store.commit('TOGGLE_DRAWER') // <--crashes the browser
}
}
}
I've searched endlessly for a solution to this problem. It's bugging me even though it visually appears to be working.
I've considered running the v-navigation-drawer in stateless mode and handling all the window resize events and state updates manually. I've also considered disabling 'Strict' mode in Vuex (which would hide the errors). But the former is a lot more complexity and the latter is a bandaid that costs me debugging insight in development.
This sounds like a perfect candidate for Lodash's debounce function. If you need to stick with using setter/getter while applying this effect, have a look at this post; otherwise, this one for sequential event subscription on any of the lifecycle hooks.
After spending some time with this, I think I have a solution. Wanted to share for anyone else that may be facing the same issue with VNavigationDrawer using Vuex state to control visibility.
The #input event passes a val parameter, which includes the state of the drawer after the window resizes. I created a new action that is called by the below function:
<v-navigation-drawer
:value="$store.state.ui.drawer"
app
clipped
#input="updateDrawer($event)"
>
Here is the action being dispatched:
methods: {
updateDrawer(event) {
if (event !== this.drawer) { // avoids dispatching duplicate actions; checks for unique window resize event
this.$store.dispatch('updateDrawer',event)
}
}
},
And the action commits the new val to the Vuex store.
Basically, the input event is able to watch for updates to the drawer, and subsequently update the drawer state if it's necessary.
You'll also see above that I stubbornly accepted using :value as the docs suggest, even though I think this should be controlled by a v-model.
Seems to be working - with the right events called and the state being updated appropriately.
I'm working on an app in React Native, and am having trouble accessing props that I feed into a component I made.
If I do console.log(this.props) within the constructor, I can see the props display in the console as desired, however if I put it in any other method, it prints undefined. How can I access the props that are clearly being sent to the component from outside of the constructor method?
You are probably adding new methods that are not binding this.
Check if you are writing the method like this:
myMethod(){
//Code
}
and just change it to:
myMethod = () => {
//Code
}
Edit: Like #Li357 says, these are called arrow functions. Arrow functions don't bind this automatically, and as a consequence receive the this of the surrounding class. In your case it will solve your issue as you want to access the properties of that class but you might want to read about it and how binding works in JS classes.
Another option is to write function.bind() but either way should work.
I'm using ElementUi NavMenu, and render function with the createElement method to make the items of the menu just using JSON with titles and index of the menu, just HTML and JS files, not .vue files.
The menu is mounted, the submenus are shown when I click it, but the actions of the submenu (el-menu-item) does not work. I even try the attributes click, item-click, v-on: click when creating the-menu-item (the documentation of ElementUi tells that #click must be used, but this causes an error on createElement when the attributes are defined), but no one works, no error occurs, as if the method was not been declared.
Only onclick attribute works on the el-menu-item, but when I use it, the method of vue component is not called, and so I have to make a function outside of component (on a class for example), and when this function is called it performs a call to component method (I try $ emits) and an error occurs, because the method of component is not found.
How can I add #click (or similar) event on the el-menu-item inside render function of the component to call a method of the same component?
Documenation of NavMenu of ElementUI.
How I'm creating menu item:
createElement("el-menu-item",{
attrs:{
index:json[i].id,
click:json[i].onclick
}},
json[i].title
)
Actually, this is mentioned in Vue.js documentation.
See https://v2.vuejs.org/v2/guide/render-function.html#The-Data-Object-In-Depth .
e.g. https://codepen.io/jacobgoh101/pen/ypjGqw?editors=0010
Vue.component("test", {
render: function(createElement) {
return createElement(
"button",
{
on: {
click: function() {
alert('click');
}
}
},
"Header"
);
}
});
Is there a way to query "up"? I'm in a Component and want to register listeners to it's parents events with control(). This requires a Query which gets me the parent of my main view.
In ExtJS4, you can use 'up()' from an Ext Element.
The params are a string of the parent element you wish to find e.g:
var parentEl = Ext.get('childID').up('div.parentClass');
If you provide some details about the structure of your components/elements I can give a specific example which should fit.
EDIT: To show going 'up' from a component
var myComponent = // however you've got it
var theParentEl = myComponent.getEl().up('div.parentClass');
Usually up('PARENTCLASS') is enough for what you're trying to do. Here is what I do all over the code so elements generates event for the form they are in:
items: [
...
{ xtype: 'checkbox', listeners: {
change: function() { this.up('window').fireEvent('checkboxchanged'); }
}}
...
]
As I understand, you want to listen to events dispatched by a component's parent from the child component's controller control function specifically.
There is not a query selector like 'parent < component' which you can put in the child controller's control function to listen to parent events.
Normally I would just add the parent view to the child's controller, then you could listen to it's events. But I assume you are not doing this because you are trying to delegate to different controllers or something.
You could fire an event in the child component whenever that parent event occurs. Inside the parent controller you could do it like this:
var child = parent.down('child');
child.fireEvent('myOwnEventName', arg1, arg2, arg3, etc);
Then you would add a handler for 'myOwnEventName' in the child controller's control function to run the logic you wanted for it.
If the parent doesn't have a controller then you should just add the parent component as a view in the child's controller.
The Sencha help says "Member expressions from candidate Components may be tested. If the expression returns a truthy value, the candidate Component will be included in the query:" in the http://docs.sencha.com/ext-js/4-0/#!/api/Ext.ComponentQuery help.
Took me a while to realize I can do the following in my controller:
this.control({
'window{down("testcomp")}[down]': { beforedestroy: this.doNotCloseIfUnsaved }
});
Using the {} operation, we can call any arbitrary code. Really bad from an efficiency standpoint, but it got the job done. I had to add the [down] because it runs component queries from right to left, so we have to be sure down() exists before we try running it (on every component). Thus, I was able to attach an event to whatever window holds my component.
Of course, other functions can be used too, like child() instead of down() if you want to ensure it is the immediate child rather than just anywhere below.