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# YUI Library Examples: Widget: Creating custom widget classes

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## Widget: Creating custom widget classes

This example shows how you can mix and match the `WidgetPostion`, `WidgetPositionExt`, `WidgetStack` and `WidgetStdMod` extensions to build custom versions of the `Widget` class, using `Base.build`.

View example in new window.

1. `Widget` with `WidgetStdMod`
   Module Header
   Module Body
   Module Footer

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2. `Widget` with `WidgetPosition, WidgetStack`
   X: Y:
   Positionable Widget

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3. `Widget` with `WidgetPosition, WidgetStack, WidgetPositionExt`

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### Creating Custom Widget Classes

The `Base` class provides a `build` method which can be used to create custom versions of classes which derive from `Base` by adding extension classes to them.

Widget currently ships with four such extensions: `WidgetPosition`, `WidgetStack`, `WidgetPositionExt` and `WidgetStdMod`. These extensions are used to build the basic `Overlay` widget, but can also be used individually, to create custom versions of the base `Widget` class.

### Widget with WidgetStdMod support

Adding the `WidgetStdMod` extension to Widget, creates a statically positioned Widget, with support for standard module format sections - header, body and footer, which maybe useful in portal type use cases, where the positioning/stacking capabilities which come bundled with Overlay are not required.

To create a custom class, we use `Base.build`, which is described in detail on the documention page for Base.

We pass in `Widget` as the main class we want to add extensions to, and `WidgetStdMod` as the extension we'd like added to the main class:

var StandardModule = Y.Base.build("standardModule", Y.Widget, [Y.WidgetStdMod]); // Render from Markup var stdmod = new StandardModule({ contentBox: "#widget1", width:"12em", height:"12em" }); stdmod.render();

`Base.build` will:

1. Create a new class which extends `Widget`
2. Aggregate known `Base` and `Widget` fields, such as `ATTRS` and `HTML_PARSER` from `WidgetStdMod` on the new class
3. Augment prototype methods from `WidgetStdMod` onto the new class prototype

The first argument to build is the `NAME` of the new class we are creating, just like the `NAME` we define when extending the Widget class directly.

Note that the `Widget` class is unchanged, allowing you to still create `Widget` instances without any standard module support, along with `StandardModule` instances which have standard module support.

#### Testing It Out

The example attempts to set content on an instance of the newly created `StandardModule` class, using the `setStdModContent` method which is added by the extension (which would otherwise not exist on the Widget instance).

var contentInput = Y.Node.get("#content"); var sectionInput = Y.Node.get("#section"); // This should work, since the StandardModule widget has settable // header/body/footer sections Y.on("click", function(e) { var content = contentInput.get("value"); var section = sectionInput.get("value"); stdmod.setStdModContent(section, content); }, "#setContent");

To verify that no unrequested features are added, we also attempt to move the instance using the `move` method, which is not part of the base Widget class, and would be added by the `WidgetPosition` extension. This verifies that the other example classes we'll create, which do create new classes which use `WidgetPosition`, have not modified the base Widget class.

// This shoud fail, since the StandardModule widget is not positionable Y.on("click", function(e) { try { stdmod.move([0,0]); } catch (e) { alert("move() is " + typeof stdmod.move + ", stdmod.hasImpl(Y.WidgetPosition) : " + stdmod.hasImpl(Y.WidgetPosition)); } }, "#tryMove");

Note that `Base.build` adds a `hasImpl` method to the built class, which allows you to query whether or not it has a particular extension applied.

#### CSS Considerations

We need to define the CSS which goes with this new `StandardModule` class we have created. The only rule really required out of the box is the rule which handles visibility (`yui-standardmodule-hidden`). The "standardmodule" used in the class name comes from the `NAME` property we set up for the new class, and is used to prefix all state related classes added to the widgets bounding box. Since the `StandardModule` class is not positionable, we use `display:none` to define the `hidden` state.

/* Visibility - How to handle visibility for this new widget */ .yui-standardmodule-hidden { display:none; }

The other "yui-standardmodule" rules are only used to create the required look/feel for this particular example, and do not impact the StandardModule widget's functionality.

### Widget with WidgetPosition and WidgetStack support

As with `StandardModule`, we use `Base.build` to create the new `Positionable` widget class. This time we add `WidgetPosition` and `WidgetStack` support to the base `Widget` class to create a basic XY positionable widget, with shimming and z-index support.

var Positionable = Y.Base.build("positionable", Y.Widget, [Y.WidgetPosition, Y.WidgetStack]); // Render from markup var positionable = new Positionable({ contentBox: "#widget2", width:"10em", height:"10em", zIndex:1 }); positionable.render("#widget2-example"); var xy = Y.Node.get("#widget2-example > p").getXY(); positionable.move(xy[0], xy[1]);

We don't add `WidgetPositionExt` or `WidgetStdMod` support, so the widget doesn't have extended positioning support (align, center) or standard module support. Hence we position it manually using the `move` method which the `WidgetPosition` extension provides.

#### Testing It Out

We should now be able to invoke the `move` method on an instance of the newly created `Positionable` class:

// This should work, since Positionable has basic XY Positioning support Y.on("click", function(e) { var x = parseInt(xInput.get("value")); var y = parseInt(yInput.get("value")); positionable.move(x,y); }, "#move");

And, as with the `StandardModule` class, we should not be allowed to invoke any methods from an extension which we didn't request:

// This should fail, since Positionable does not have Standard Module sections Y.on("click", function(e) { try { positionable.setStdModContent("header", "new content"); } catch (e) { alert("setStdModContent() is " + typeof positionable.setStdModContent + ", positionable.hasImpl(Y.WidgetStdMod) : " + positionable.hasImpl(Y.WidgetStdMod)); } }, "#tryContent");

#### CSS Considerations

Since now we have a positionable widget, with z-index support, we set the widget to be absolutely positioned by default, and control it's hidden state using `visibility` as opposed to `display`

/* Define absolute positioning as the default for positionable widgets */ .yui-positionable { position:absolute; } /* In order to be able to position the widget when hidden, we define hidden to use visibility, as opposed to display */ .yui-positionable-hidden { visibility:hidden; }

### Widget with WidgetPosition, WidgetStack and WidgetPositionExt support

Lastly, we'll attempt to create a new widget class, which, in addition to basic positioning and stacking support, also has extended positioning support, allowing us to align it with other elements on the page.

Again, we use `Base.build` to create our new `Alignable` widget class, by combining `WidgetPosition`, `WidgetStack` and `WidgetPositionExt` with the base widget class:

var Alignable = Y.Base.build("alignable", Y.Widget, [Y.WidgetPosition, Y.WidgetPositionExt, Y.WidgetStack]); var alignable = new Alignable({ width:"13em", align : { node: "#widget3-example", points: ["cc", "cc"] }, zIndex:1 }); alignable.get("contentBox").set("innerHTML", '<strong>Alignable Widget</strong><div id="alignment"><p>#widget3-example</p><p>[center, center]</p></div>'); alignable.render("#widget3-example");

#### Testing It Out

We'll attempt to align an instance of the `Alignable` class, using some of the additional attributes which `WidgetPositionExt` adds to the base `Widget` class: `align` and `centered`:

// Align left-center egde of widget to right-center edge of the node with id "widget3-example" alignable.set("align", {node:"#widget3-example", points:["lc", "rc"]}); // Align top-right corner of widget to bottom-right corner of the node with id "widget3-example" alignable.set("align", {node:"#widget3-example", points:["tr", "br"]}); // Center the widget in the node with id "widget3-example" alignable.set("centered", "widget3-example"); // Align the right-center edge of the widget to the right center edge of the viewport (since a node is not provided to 'align') alignable.set("align", {points:["rc", "rc"]}); // Center the widget in the viewport (wince a node is not provided to 'centered') alignable.set("centered", true); // Return the node to it's original alignment (centered in the node with id "widget3-example") // NOTE: centered is a shortcut for align : { points:["cc", "cc"] } alignable.set("align", {node:"#widget3-example", points:["cc", "cc"]});

#### CSS Considerations

The `Alignable` widget class, has the same core CSS rules as the `Positionable` class, to define how it is positioned and how it is hidden:

/* Define absolute positioning as the default for alignable widgets */ .yui-alignable { position:absolute; } /* In order to be able to position the widget when hidden, we define hidden to use visibility, as opposed to display */ .yui-alignable-hidden { visibility:hidden; }

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