NativeScript - how can I filter an observable array with SearchBar? - filtering

Question

Hi I'm trying to filter an observable array of data fetched via a HTTP request on keypress of the SearchBar.
I managed to get the SearchBar property change to work but I can't seem to figure out what I'm doing wrong in the filtering logic.
Ideally I want to update the list as I type in the search term in the SearchBar. I've searched the API on the Telerik site, there wasn't really any examples I could find.
XML
<Page loaded="pageLoaded">
<ActivityIndicator busy="{{ isLoading }}" />
<ActionBar title="People">
</ActionBar>
<GridLayout>
<StackLayout>
<SearchBar id="searchBar" hint="Search for someone"></SearchBar>
<ListView items="{{ peopleList }}" itemTap="showDetail">
<ListView.itemTemplate>
<StackLayout>
<Label text="{{ fullName }}" horiztonalAlignment="left" verticalAlignment="center"></Label>
<Label text="{{ company }}" class="info"></Label>
</StackLayout>
</ListView.itemTemplate>
</ListView>
</StackLayout>
</GridLayout>
</Page>
JS
var frames = require("ui/frame");
var Observable = require("data/observable").Observable;
var PeopleListViewModel = require("../../shared/people-viewModel");
var activityIndicatorModule = require("ui/activity-indicator");
var page;
var userkey;
var peopleList = new PeopleListViewModel([]);
var pageData = new Observable({ peopleList: peopleList });
exports.pageLoaded = function(args) {
page = args.object;
page.bindingContext = pageData;
userkey = userkey || page.navigationContext.userkey;
peopleList.load(userkey); // fetch data from the backend
var searchBar = page.getViewById("searchBar");
searchBar.on("propertyChange", function (args) {
var searchText = args.object.text;
if (searchText === "") {
// NOT SURE WHAT TO DO HERE.
} else {
peopleList.filter(function (element, index, array) {
// DOESN"T WORK PROPERLY
console.log("element: ", JSON.stringify(element));
return element.fullName == searchText;
});
console.log("Text types: ", searchText);
}
});
};
exports.showDetail = function(args) {
var person = peopleList.getItem(args.index);
var navigateEntry = {
moduleName: "views/people/people-detail",
context: { person: person },
animated: false
};
frames.topmost().navigate(navigateEntry);
};
PeopleListViewModel.js
var config = require("./config");
var fetchModule = require("fetch");
var ObservableArray = require("data/observable-array").ObservableArray;
function PeopleListViewModel(people) {
var viewModel = new ObservableArray(people);
viewModel.load = function (userKey) {
return fetchModule.fetch(config.baseUrl + "/api/people/all/" + userKey)
.then(function (response) {
return response.json();
})
.then(function (data) {
data.forEach(function (person) {
viewModel.push(person);
});
}, function (error) {
console.log("Error: ", error);
});
};
viewModel.empty = function () {
while (viewModel.length) {
viewModel.pop();
}
};
return viewModel;
}
function handleErrors(response) {
if (!response.ok) {
console.log("Error occurred");
}
}
module.exports = PeopleListViewModel;
Updated people-list
var frames = require("ui/frame");
var Observable = require("data/observable").Observable;
var ObservableArray = require("data/observable-array").ObservableArray;
var PeopleListViewModel = require("../../shared/people-viewModel");
var activityIndicatorModule = require("ui/activity-indicator");
var page;
var userkey;
var peopleList = new PeopleListViewModel([]);
var pageData = new Observable({ peopleList: peopleList });
var resultList = new ObservableArray([]);
exports.pageLoaded = function(args) {
page = args.object;
page.bindingContext = pageData;
userkey = userkey || page.navigationContext.userkey;
peopleList.load(userkey);
var searchBar = page.getViewById("searchBar");
searchBar.on("propertyChange", function (args) {
var searchText = args.object.text;
if (searchText === "") {
} else {
while (resultList.length > 0) {
resultList.pop();
}
peopleList.forEach(function (element) {
if (element.fullName === searchText) {
resultList.push(element);
}
});
}
});
};

Answer 1

I had the same issue. If you want to filter your data after every character has changed in search-bar you can try my solution.
Definitions
My playerList is your peopleList. This is the data from view-model.
resultList is an array where the data will be pushed.
var observableArrayModule = require("data/observable-array").ObservableArray;
var playerList = new PlayerListViewModel([]);
var resultList = new observableArrayModule([]);
var pageData = new observableModule.Observable({
resultList: resultList,
player: ""
});
Inside expors.loaded()
page = args.object;
searchBar = page.getViewById("search-bar");
page.bindingContext = pageData;
Load Initial Data - inside expors.loaded()
We are loading initial data when user navigates to the screen for the first time. We are also pushing the same data to resultList since we are using {{resultList}} in xml. You can add loadingIndicator while the list is populated.
playerList
.load()
.then(function() {
setTimeout(function() {
playerList.forEach(function (element) {
pageData.resultList.push(element);
});
}, 1000);
})
.catch(function(error) {
dialogsModule.alert({
message: "An error occurred while loading players.",
okButtonText: "OK"
});
});
Clear autofocus - inside expors.loaded()
This is to prevent keyboard from opening on initial screen navigation.
if (searchBar.ios) {
searchBar.ios.endEditing(true);
} else if (searchBar.android) {
searchBar.android.clearFocus();
}
Search data when character has changed - inside expors.loaded()
I am calling filter functionality. Lodash _.debounce function is used to delay looping through resultList array. Without it, the app would loop every time letter is typed. Now we are waiting for user to stop typing to start looping.
searchBar.on('propertyChange', _.debounce(searchList, 500));
searchList Function
This is the actual loop. You can change element.name for your needs.
function searchList(args) {
var searchText = args.object.text;
while(resultList.length > 0) {
resultList.pop();
}
playerList.forEach(function (element) {
if (element.name.toLowerCase().indexOf(searchText) >= 0) {
resultList.push(element);
}
});
}
Hide keyboard if search-bar is cleared - inside exports.loaded()
And finally we want to hide the keyboard if user clears the search-bar.
searchBar.on(searchBarModule.SearchBar.clearEvent, function (args) {
setTimeout(function() {
searchBar.dismissSoftInput();
}, 10);
});
PS
You probably solved your issue, but this could help someone else in the future.

Answer 2

Okay so your problem is a Javascript problem than a NativeScript problem. For the sake of this problem, think of observable arrays as just your ordinary arrays.
In your JS you're creating a new PeopleListViewModel which you're then attaching to the bindingContext via the pageData object. So far so good. Then you're calling the load method on the PeopleListViewModel (It returns a promise which you're not really doing anything with but for this specific problem it doesn't matter).
However, when text is inputed you're not really doing anything. This is your code:
peopleList.filter(function (element, index, array) {
// DOESN"T WORK PROPERLY
console.log("element: ", JSON.stringify(element));
return element.fullName == searchText;
});
peopleList is an instance of PeopleListViewModel which returns an ObservableArray. The ObservableArray does indeed have a method called filter (which works just like filter of a regular array. Check out the NativeScript documentation and Javascript documentation of filter).
What you need to understand here is that filter returns a new array with the filtered results. Doing peopleList.filter() will send that new array into empty space. You want to var yourNewFilteredArray = peopleList.filter(). But you don't really want to redefine the array bound to the binding context, you want to modify the content of it.
Here's an example of how you could do that:
/*
* Attach a new obsersable array to the binding context.
* you can prepopulate it with the data from the
* PeopleListViewModel if you want to
*/
var resultList = new ObservableArray([]);
var pageData = new Observable({ resultList: resultList });
/*
* Then on search/filter you want to modify this new
* array. Here I first remove every item in it and then
* push matching items to it.
*/
searchBar.on("propertyChange", function (args) {
var searchText = args.object.text;
// ...
while(resultList.length > 0) {
resultList.pop();
}
peopleList.forEach(function (element) {
if (element.fullName === searchText) {
resultList.push(element);
}
});
});