Added collection of FormItemArgs for each of the form FormItem types

[mikeschinkel]

After working with Forms for a while and requesting several PRs to make working with them easier I finally had enough with the complexity and decided to implement an alternate method to add form fields than <form>.AddInputField(), <form>.AddPasswordField(), <form>.AddDropdown(), and <form>.AddCheckbox().

The *biggest problem I was trying to fix were that once a field was added it was tedious to then access the form to set other properties not allow to be set in the FormItems New...() method. So I tried numerous iterations with the absolute requirement of backward compatibility and came up with the following, by example:

type Object struct {
    Name     string
    Birthday string
    Password string
    Confirm  string
    FavColor string
    Website  string
    Customer bool
}
type Strings [] string

func (ss Strings) Index(str string) int {
    pos := -1
    for i, v := range ss {
        if v != str {
            continue
        }
        pos = i
        break
    }
    return pos
}

var colors = Strings{"Red", "Green", "Blue"}

func AddFields(form *tview.Form, obj Object) *tview.Form {
    return form.Clear(true).
        AddFormItem(NewInputField(), &InputFieldArgs{
            Label:       "Name:",
            Text:        obj.Name,
            FieldWidth:  40,
            Placeholder: "Enter your full name",
        }).
        AddFormItem(NewInputField(), &InputFieldArgs{
            Label:      "Birthday:",
            Text:       obj.Birthday,
            FieldWidth: 12,
            DoneFunc: func(key tcell.Key) {
                // do something with birthday
            },
        }).
        AddFormItem(NewDropDown(), &DropDownArgs{
            Label:         "Favorite Color?",
            Options:       colors,
            InitialOption: colors.Index(obj.FavColor),
            SelectedFunc: func(option string, optionIndex int) {
                // do something with selected option
            },
        }).
        AddFormItem(NewInputField(), &InputFieldArgs{
            Label:                "Website:",
            Text:                 obj.Website,
            FieldWidth:           60,
            FieldBackgroundColor: tcell.ColorAliceBlue,
            FieldTextColor:       tcell.ColorGreen,
        }).
        AddFormItem(NewCheckbox(), &CheckboxArgs{
            Label:   "Customer?",
            Checked: obj.Customer,

        }).
        AddFormItem(NewPasswordField(), &PasswordFieldArgs{
            Label:      "Password:",
            Text:       obj.Password,
            FieldWidth: 30,
        }).
        AddFormItem(NewPasswordField(), &PasswordFieldArgs{
            Label:      "Confirm:",
            Text:       obj.Confirm,
            FieldWidth: 30,
        })
}

I would have preferred to use the names AddInputField() etc. but could not do so w/o breaking old code so I extended AddFormItem() instead.

There is also a ton of effectively duplicated code, but given the structure of the existing code I could not find a way to consolidate code without breaking backward compatibility. If breaking backward compatibility is an option, I could change the code to be more maintainable, but I needed the functionality and I assumed you would be much less likely to access broken backward compatibility so I went ahead and implemented as is.

Hopefully you will concur this is a good addition to tview and accept this PR? Thanks in advance for considering.

[mikeschinkel]

@rivo:

I wanted to follow up with some links showing this feature in action:

1. https://github.com/newclarity/blueprintz/blob/master/browseui/layout_view.go#L41
2. https://github.com/newclarity/blueprintz/blob/master/browseui/core_view.go#L30
3. https://github.com/newclarity/blueprintz/blob/master/browseui/project_view.go#L76