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koGrid: Get reference to grid for direct manipulations

January 26th, 2017 Admin No comments

    Having used the koGrid on the page, sometimes you may need to manipulate with the grid directly, for example, to programmatically select or deselect items and so on. For this you need to get a reference to the grid instance first. The koGrid supports plugins to enhance and extend grid’s capabilities. Each plugin should expose the onGridInit method being called from the koGrid-binding and fed with the grid instance, which can be saved and used later. Below is a fragment of the koGrid-binding where the plugins are being initialized:

// koGrid-2.1.1.debug.js
ko.bindingHandlers['koGrid'] = (function () {
  return {
    'init': function (element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {
       var options = valueAccessor();
       ...
       var grid = new window.kg.Grid(options);
       ...
       //initialize plugins
       $.each(grid.config.plugins, function (i, p) {
          if (typeof p.onGridInit === 'function') {
             p.onGridInit(grid);
          }
       });
       ...
       return { controlsDescendantBindings: true };
    }
  };
}());

Let’s create a plugin to capture the reference to the grid. The following simple typescript class keeps the reference and exposes it to outer code. Note the use of ko.utils.domNodeDisposal.addDisposeCallback to release the reference if the grid disappears from the DOM-model (for example, being wrapped in if- or with-bindings).

// typescript
export class KoGridRef {

  public grid = null;

  public onGridInit(grid) {
    // save the reference
    this.grid = grid;

    var self = this;
    // hook up the node removing to release the reference to the grid instance
    ko.utils.domNodeDisposal.addDisposeCallback(grid.$root[0], function() {
      self.grid = null;
    });
  }
}

Below is how to declare, attach and use the plugin

// typescript

// declare
private gridRef: KoGridRef = new KoGridRef();

// attach
public koGridOptions = ko.pureComputed(() => {
  return {
    data: this.items, // observable array of data
    selectedItems: this.selectedItems, // observable array to store selected items
    plugins: [gridRef], // array of plugins
    ...
  }
});

// use
public get grid() { // property to return the grid instance
  return this.gridRef.grid;
}	

public selectAll(grid: any, state: boolean) { // method to select or deselect all items
  grid.allSelected(state);
}
...
this.selectAll(this.grid, Math.random() >= 0.5); // randomly select or deselect all items
...
Related posts:

koGrid: Bug – Checkboxes column duplication

January 24th, 2017 Admin No comments

    Using the koGrid to bring an edit-in-place grid to a web app, I’ve run into a bug when the predefined first column of checkboxes are being unexpectedly replicated, i.e. being wrapped in the if-binding, the grid has as many checkboxes columns as many times its presence has been changed.

koGrid: Checkbox Column Duplication Bug

I use the following to define the grid

<!-- ko if: shouldGridBeVisible -->
   <div data-bind="koGrid: koGridOptions()"></div>
<!-- /ko -->
// typescript
private customKoGridColumnDefs = [
   { field: 'Name', displayName: 'Name' },
   ...
];

private koGridColumnDefs = ko.pureComputed(() => {
   return this.customKoGridColumnDefs;
});

public koGridOptions = ko.pureComputed(() => {
   return {
      data: this.items, // observable array of data
      selectWithCheckboxOnly: true, // only want to be able to select with checkboxes
      selectedItems: this.selectedItems, // observable array to store selected items
      columnDefs: this.koGridColumnDefs, // observable columns definitions
      displaySelectionCheckbox : true // show column of checkboxes
      ...
   }
});

The “buggy” place is within the buildColumns function defined in the window.kg.Grid. Among other things the function adds a column of checkboxes to the existing columns definitions, not checking if such column is already there. Below are shortened listings of the buildColumns and related functions, ending with koGrid-binding

// koGrid-2.1.1.debug.js
window.kg.Grid = function (options) {
   ...
   self.config.columnDefs = ko.utils.unwrapObservable(options.columnDefs);
   ...
   self.buildColumns = function () {
      var columnDefs = self.config.columnDefs,
         cols = [];

      if (!columnDefs) {
         self.buildColumnDefsFromData();
         columnDefs = self.config.columnDefs;
      }
      if (self.config.displaySelectionCheckbox && self.config.canSelectRows) {
         // the columns definitions array passed in the options is about to be modified
         columnDefs.splice(0, 0, {
            field: '\u2714',
            width: self.elementDims.rowSelectedCellW,
            sortable: false,
            resizable: false,
            headerCellTemplate: '<input class="kgSelectionHeader" type="checkbox" data-bind="visible: $grid.multiSelect, checked: $grid.allSelected" />',
            cellTemplate: '<div class="kgSelectionCell"><input class="kgSelectionCheckbox" type="checkbox" data-bind="checked: $parent.selected" /></div>'
         });
      }
   ...
   };
   ...
   self.init = function () {
      ...
      self.buildColumns(); // build columns
      ...
   };
   ...
   self.init(); // initialize grid
};
...
ko.bindingHandlers['koGrid'] = (function () {
   return {
      'init': function (element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {
         var options = valueAccessor();
         ...
         var grid = new window.kg.Grid(options); // create and initialize grid
         ...
         // if columndefs are observable watch for changes and rebuild columns.
         if (ko.isObservable(options.columnDefs)) {
            options.columnDefs.subscribe(function (newDefs) {
               grid.columns([]);
               grid.config.columnDefs = newDefs;
               grid.buildColumns(); // rebuild the columns
               grid.configureColumnWidths();
            });
         }
         ...
         return { controlsDescendantBindings: true };
      }
   };
}());

So, whenever if-binding’s conditions are met, the grid becomes visible, and we have the following call sequence:

ko.bindingHandlers['koGrid'].init -> window.kg.Grid.init -> window.kg.Grid.buildColumns

which ends up with adding the next-in-turn checkboxes column to the columns definitions and, therefore, to the grid. The same, by the way, may happen also if the columns definitions (options.columnDefs) are observable and being mutated (line 49 in the listing above).

It’s a well-known issue (I was able to find at least 2 describing this bug: #292 and #209) with a simple fix already residing among the pull requests (#213), but not applied yet (and may never be applied as the project have not been updated since 2014 and looks abandoned). The fix is to the window.kg.Grid.buildColumns and shown below:

// koGrid-2.1.1.debug.js
self.buildColumns = function () {
   var columnDefs = self.config.columnDefs,
      cols = [];

   if (!columnDefs) {
      self.buildColumnDefsFromData();
      columnDefs = self.config.columnDefs;
   }
   if (self.config.displaySelectionCheckbox && self.config.canSelectRows) {
      if (columnDefs.length > 0 && columnDefs[0].field != '\u2714') {
         columnDefs.splice(0, 0, {
            field: '\u2714',
            width: self.elementDims.rowSelectedCellW,
            sortable: false,
            resizable: false,
            headerCellTemplate: '<input class="kgSelectionHeader" type="checkbox" data-bind="visible: $grid.multiSelect, checked: $grid.allSelected"/>',
            cellTemplate: '<div class="kgSelectionCell"><input class="kgSelectionCheckbox" type="checkbox" data-bind="checked: $parent.selected" /></div>'
         });
      }
   }
   ...
};

I really don’t like changing the 3rd party libraries’ source code in my projects and always try to find an alternative way. This issue can be resolved with the fix utilizing the knockout.js‘s power and placed outside of the koGrid-2.1.1.debug.js and koGrid-2.1.1.js. So, below is the binding-wrapper to prevent duplication right before the original koGrid-binding gets control:

// javascript
ko.bindingHandlers["koGridFixed"] = {
   init: function (element, valueAccessor, allBindingsAccessor, data, context) {
      var gridOptions = ko.utils.unwrapObservable(valueAccessor());
      if (gridOptions && gridOptions.columnDefs) {
         var columnDefsArr = ko.utils.unwrapObservable(gridOptions.columnDefs);
         if (columnDefsArr && columnDefsArr.length > 0 && columnDefsArr[0].field === '\u2714')
            columnDefsArr.splice(0, 1);
      }

      return ko.bindingHandlers["koGrid"].init(element, valueAccessor, allBindingsAccessor, data, context);
   }
};

So, just replace the koGrid-binding everywhere in views with the koGridFixed and the problem is solved with no affecting the grid’s source code

<!-- ko if: shouldGridBeVisible -->
   <div data-bind="koGridFixed: koGridOptions()"></div>
<!-- /ko -->
Related posts:

Knockout.js: Subscription that fires only once

November 16th, 2016 Admin No comments

    It might be useful sometimes to have an observable subscription, which fires only once. The straightforward implementation is to use kind of “already fired” internal flag that would prevent a handler from being called more than once. It’s not the best approach though, as the subscription itself remains alive and continues firing every time the value has mutated. Much more efficient solution is to “kill” subscription by disposing it at the first call:

ko.subscribable.fn.subscribeOnce = function (handler, target, event) {
    var subscription = this.subscribe(function (newValue) {
        subscription.dispose(); // remove subscription, so it won't fire further
        handler(newValue);
    }, target, event);

    return subscription; // mimic the normal "subscribe" by returning the subscription
};

In case of computed observables, it gives even more benefits since it also removes all underlying subscriptions to other observables the computed observable depends on.

In TypeScript this will be an extension to the KnockoutSubscribableFunctions<T> interface

// knockoutjs-extensions.d.ts
interface KnockoutSubscribableFunctions<T> {
    subscribeOnce(callback: (newValue: T) => void, target?: any, event?: string): KnockoutSubscription;
    subscribeOnce<TEvent>(callback: (newValue: TEvent) => void, target: any, event: string): KnockoutSubscription;
}

TypeScript has the “declaration merging” concept, so the interfaces are “open-ended”. That means two or more separate declarations with the same name are to be merged by compiler into a single one. Note, to be effective the declaration has to be placed in a TypeScript Declaration File (*.d.ts).

Below is a usage example

...
private someObservable: KnockoutObservable<SomeType> = ko.observable(null);
...
this.someObservable.subscribeOnce(newVal => {
	// do something here
});

Select2: Custom matcher and highlighting

September 28th, 2015 Admin No comments

    The Select2 uses the “contains”-matcher by default. In case of a big number of options, we’ve run into the time lag whenever the drop-down appears with the filtered out items. Of course, we could increase the minimumInputLength setting to minimize items within the drop-down. We, however, decided to change the algorithm used for filtering. The method below looks for options, any word of which is starting with the pattern typed in.

function wordStartMatcher(term, text, highlighting) {
	var myRe  = new RegExp("(?:^|\\s)" + term, "i");
	var match = myRe.exec(text);

	if (match != null && highlighting) {
		myRe = new RegExp("\\b" + term, "i");
		match = myRe.exec(text);
	}

	return match;
}

The method is used twice: for filtering out and for highlighting the found pattern in options. Two regexps in the method do the same, they both capture the beginning of each word. However, they handle Unicode in different ways. So the first one accurately chooses options that match while the second one fetches out the parts of the options to be highlighted.

Below is the method responsible for highlighting

function markMatch(text, term, markup, escapeMarkup) {
	var wordMatch = wordStartMatcher(term, text, true);

	var match = wordMatch ? wordMatch.index : -1;
	var tl = term.length;

	if (match < 0) {
		markup.push(Select2.util.escapeMarkup(text));
		return;
	}

	markup.push(Select2.util.escapeMarkup(text.substring(0, match)));
	markup.push("<span class='select2-match'>");
	markup.push(Select2.util.escapeMarkup(text.substring(match, match + tl)));
	markup.push("</span>");
	markup.push(Select2.util.escapeMarkup(text.substring(match + tl, text.length)));
}

The method fetches out the string part which meets the pattern and wraps it in special tags.

Ok, now is how to apply the custom matcher and highlighing to the Select2 control

$("#magazines").select2({
	matcher: function (term, text) {
		return wordStartMatcher(term, text) != null;
	},
	formatResult: function (result, container, query, escapeMarkup) {
		var markup = [];
		markMatch(this.text(result), query.term, markup, escapeMarkup);
		return markup.join("");
	}
});

Where the “#magazines“-control from the example is specified as

<select id="magazines" name="magazines">
	<option value="">Select a subscription</option>
	<option value="Msdn">MSDN Magazine</option>
	<option value="VS">Visual Studio Magazine</option>
	<option value="Code">CODE Magazine</option>
	<option value="Dobbs">Dr. Dobbs Journal</option>
	<option value="GameDev">Game Developer Magazine</option>
	<option value="LinUsDev">Linux User and Developer</option>
</select>

So, for the above listed options and the pattern defined as “u” the “contains”-matcher would give

  • Visual Studio Magazine
  • Dr. Dobbs Journal
  • Linux User and Developer

while the custom matcher gives what we really need

  • Linux User and Developer

Categories: HTML, JavaScript, Select2 Tags: , ,

Knockout.js Validation: Check if value is in range

June 20th, 2015 Admin No comments

    To validate a model and its properties (observable and ordinary ones) we use such knockout.js plugin as Knockout Validation. This validation library is simple and easy to extend. For example, a new validation rule to check if value is in range could be as simple as the following:

import ko = require("knockout");
import validation = require("knockout.validation");
...
export function enableCustomValidators() {

 validation.rules['inRange'] = {
  validator: function (val, params) {
   var minVal = ko.validation.utils.getValue(params.min);
   var maxVal = ko.validation.utils.getValue(params.max);

   var res = params.includeMin ? val >= minVal : val > minVal;

   if (res)
    res = params.includeMax ? val <= maxVal : val < maxVal;

   if (!res)
    this.message = ko.validation.formatMessage(params.messageTemplate || this.messageTemplate,
       [minVal, maxVal, (params.includeMin ? '[' : '('), (params.includeMax ? ']' : ')') ]);

   return res;
   },
   messageTemplate: 'Value has to be in range {2}{0}, {1}{3}'
 };

 validation.registerExtenders(); // adds validation rules as extenders to ko.extenders
}
...
// the enableCustomValidators should be called when the custom
// validation rules are supposed to be used

Note the code above and further is TypeScript. The TypeScript definition to the Knockout Validation is available as a NuGet package, namely knockout.validation.TypeScript.DefinitelyTyped.

The inRange rule accepts the start and end values and allows to indicate should or should not they be included in the range (by default boundaries are excluded). The validation error message is being generated based on the custom defined messageTemplate or default one. The default message template uses four placeholders where the {0} and {1} are start and end values correspondingly. The latter two represent brackets: square or round ones depending on the boundaries inclusion.

The example below defines inRange validation to keep the value between 0 (including it) and 10 (excluding it):

public someNumber = ko.observable<number>(null).extend(
{
	required: { params: true, message: "This field is required" },
	number:   { params: true, message: "Must be a number" },

	inRange:  {
		params: {
			min: 0,
			includeMin: true,
			max: 10,
			//includeMax: true,
		}
	}
});

In case of a wrong value the message will says “Value has to be in range [0, 10)".

To redefine the message template the following might be used:

public somePositiveNumber = ko.observable<number>(null).extend(
{
 required: { params: true, message: "This field is required" },
 number:   { params: true, message: "Must be a number" },

 inRange:  {
  params: {
   min: 0,
   max: 1,
   messageTemplate: "Must be a positive number less than {1}"// the range end value will be put
  }
 }
});

Note the ko.validation.formatMessage has been used to generate the final validation message. Till recently the ko.validation.formatMessage wasn't able to process more than one placeholder in template. So, if you use one of such outdated versions of Knockout Validation library, you may be interested in the actual formatting method implementation shown below. It's borrowed from the same Knockout Validation, but of up-to-date version.

function formatMessage(message, params, observable?) {
    if (ko.validation.utils.isObject(params) && params.typeAttr) {
        params = params.value;
    }
    if (typeof message === 'function') {
        return message(params, observable);
    }
    var replacements = ko.utils.unwrapObservable(params);
    if (replacements == null) {
        replacements = [];
    }
    if (!ko.validation.utils.isArray(replacements)) {
        replacements = [replacements];
    }
    return message.replace(/{(\d+)}/gi, function (match, index) {
        if (typeof replacements[index] !== 'undefined') {
            return replacements[index];
        }
        return match;
    });
}