ExtJS: How to create own Class with other ExtJS components?

Question

I am trying to create Panel class object with different items. Basically its related with Desktop app in ExtJS.
DetailView.js

Ext.define("App.view.DetailView", {
   extend : 'Ext.panel.Panel',
   alias : 'widget.asset-panel',
   itemId : 'Detail-view',
   region : 'center',
   initComponent : function() {
      this.items = [ comboboxes, customPanel ];
      this.callParent(arguments);
   }
});  

I am trying to create items component in both the way i.e. using xtype and using Ext.create() way. I am not sure which is correct and how should I got about it.. below is comboboxes variable inside DetailView.js

var comboboxes = {
xtype : 'form',
border : false,
padding : '5 5 5 5',
items : [ {
    layout : 'column',
    border : false,
    width : 600,
    items : [ {
        xtype : 'combobox',
        columnWidth : .15,
        itemId : 'filter-1',
        store : [ 'Employee', 'Manager', 'TeamLead' ]
    }, {
        xtype : 'combobox',
        columnWidth : .15,
        margin : '0, 0, 0, 15',
        store : [ 'Keywords', 'Names' ]
    }, {
        xtype : 'combobox',
        columnWidth : .15,
        margin : '0, 0, 0, 15',
        store : [ 'Some Data here' ]
    }]
} ]
};  

So far so good, If I am keeping this.items = [comboboxes] in DetailView class its working fine without any issue. but when I am trying to add other component, such as customPanel inside DetailView.js

var custom = Ext.create('Ext.panel.Panel', {
itemId : 'panel_1',
height : 300,
border : false,
layout : 'card',
items : [ {
    xtype : 'container',
    itemId : 'listCt',
    layout : {
        type : 'vbox',
        align : 'stretch'
    },
    defaults : {
        margin : 2
    },
    items : []
}, {
    xtype : 'container',
    itemId : 'fitCt',
    layout : 'fit'
} ]
});  

I tried both the way to initialize panel, as in above and by using initComponent() but every time it gives error:

Uncaught TypeError: Cannot set property 'component' of null ext-all.js:22
Ext.cmd.derive.privates.finishRender ext-all.js:22
Ext.cmd.derive.finishRenderItems ext-all.js:22
Ext.cmd.derive.finishRender ext-all.js:22
Ext.cmd.derive.privates.finishRenderChildren ext-all.js:22
Ext.cmd.derive.afterRender ext-all.js:22
Ext.cmd.derive.privates.finishRender ext-all.js:22
Ext.cmd.derive.finishRenderItems ext-all.js:22
Ext.cmd.derive.finishRender ext-all.js:22
Ext.cmd.derive.privates.finishRenderChildren ext-all.js:22
Ext.cmd.derive.afterRender ext-all.js:22
Ext.cmd.derive.privates.finishRender ext-all.js:22
Ext.cmd.derive.finishRenderItems ext-all.js:22
Ext.cmd.derive.finishRender ext-all.js:22
Ext.cmd.derive.privates.finishRenderChildren ext-all.js:22
Ext.cmd.derive.afterRender ext-all.js:22
Ext.cmd.derive.afterRender ext-all.js:22
Ext.cmd.derive.privates.finishRender ext-all.js:22
Ext.cmd.derive.render ext-all.js:22
Ext.cmd.derive.privates.doAutoRender ext-all.js:22
Ext.cmd.derive.show ext-all.js:22
Ext.define.restoreWindow Desktop.js?_dc=1406637300888:388
Ext.define.onShortcutItemClick Desktop.js?_dc=1406637300888:199
fire ext-all.js:22
doFireEvent ext-all.js:22
a.doFireEvent ext-all.js:22
fireEventArgs ext-all.js:22
fireEvent ext-all.js:22
Ext.cmd.derive.processUIEvent ext-all.js:22
Ext.cmd.derive.handleEvent ext-all.js:22
Ext.cmd.derive.doFire ext-all.js:22
Ext.cmd.derive.fire ext-all.js:22
Ext.cmd.derive.doDispatchEvent ext-all.js:22
Ext.cmd.derive.dispatch ext-all.js:22
Ext.cmd.derive.dispatch ext-all.js:22
Ext.cmd.derive.doPublish ext-all.js:22
Ext.cmd.derive.publish ext-all.js:22
Ext.cmd.derive.onDelegatedEvent ext-all.js:22
(anonymous function)  

it gives error when reinitialing window. i.e. it work only in first execution, but not in second. I doubt if components are being render and destroyed properly. What could be the possible reason ? any possible solution ?

Answer 1

It seems that you're reusing the components after they've been destroyed:

initComponent : function() {
    // comboboxes & customPanel will be the same instances 
    // for every App.view.DetailView you create
    this.items = [ comboboxes, customPanel ];
    this.callParent(arguments);
}

The same here:

items : [{
    xtype : 'container',
    itemId : 'listCt',
    // ...

    // The component in this items variable will be destroyed when their
    // parent is destroyed, and won't be usable again after that
    items : items

    // ...
}]

You've got two solid ways to define custom classes with preset items.

First, you can use inline (xtype) configuration. This has the advantage of lazy initialization; further, Ext will create separate instances of the items each time you create an instance of your custom component.

For example:

Ext.define('My.Panel', {
    extend: 'Ext.panel.Panel'

    ,items: [{
        xtype: 'textfield'
        ,fieldLabel: "My field"
    },{
        xtype: 'component'
        ,html: "Bla bla bla"
    }]
});

var myFirstPanel = new My.Panel({
    renderTo: Ext.getBody()
    ,title: "First Panel"
});

var mySecondPanel = new My.Panel({
    renderTo: Ext.getBody()
    ,title: "Second Panel"
});

If you need more involved treatment, hook on the initComponent method, but be sure to create new instances of the child items in there.

Ext.define('My.InitComponentPanel', {
    extend: 'Ext.panel.Panel'

    ,customFieldLabel: "Example field"

    ,initComponent: function() {

        // initComponent will be called each time a InitComponentPanel
        // is created, and a new textfield will be created for each

        this.items = [
            new Ext.form.field.Text({
                fieldLabel: this.customFieldLabel
            });
        ];

        this.callParent(arguments);
    }
});

var panel1 = new My.InitComponentPanel({
    renderTo: Ext.getBody()
    ,customFieldLabel: "First field"
});

// will destroy panel1's items, but no problem
panel1.destroy();

var panel2 = new My.InitComponentPanel({
    renderTo: Ext.getBody()
    ,customFieldLabel: "Second field"
});

The same goes if you use Ext components directly (without extending them); don't use existing components in multiple places.

// Inline (uninstantiated) items are always fine
var panel = new Ext.panel.Panel({
    renderTo: Ext.getBody()
    ,items: [{
        xtype: 'checkbox'
        ,boxLabel: "My checkbox"
    }]
});

// You can also create children beforehand
var checkbox = new Ext.form.field.Checkbox;
var panel2 = new Ext.panel.Panel({
    renderTo: Ext.getBody()
    ,items: [checkbox]
});

// But don't reuse the checkbox for another panel
var panel3 = new Ext.panel.Panel({
    renderTo: Ext.getBody()
    // this will remove the unique checkbox instance from panel2
    // and if panel2 has been destroyed meanwhile, it will crash
    ,items: [checkbox]
});

Don't forget that you can also add/remove items from a container that has already been created with its add, insert, remove, etc. methods (but don't touch the items property directly!).