Apple Newton Utilities Guia do Utilizador descarregar pdf (Página 225)

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CHAPTER 6

Pickers, Pop-up Views, and Overviews

Overview Protos 6-25

You also need to deﬁne the following slot in your protoOverview:

cursor This should be a cursor-like object.

You use the object stored in this slot to encapsulate your data. The cursor-like

object must support the methods

Entry, Next, Move, and Clone. An example is

given below.

In addition, you must provide a mechanism to ﬁnd an actual data item given an

index of a displayed item. In general, you need some sort of saved index that

corresponds to the ﬁrst displayed item. See the example code in “HitItem”

(page 5-88) in Newton Programmer’s Reference for an example of how this is used.

You also should provide a mechanism to track the currently highlighted item,

which is distinct from a selected item.

Since your data is probably in an array, you can use a “cursor” object like this:

{ items: nil,

index: 0,

Entry:func()

begin

if index < Length(items) then

items[index];

end,

Next: func()

if index < Length(items)-1 then

begin

index := index + 1;

items[index];

end,

Move: func(delta)

begin

index := Min(Max(index + delta, 0),

kNumItems-1) ;

items[index];

end,

Clone:func()

Clone(self)}

The methods that you need to have in the cursor-like object are:

■ Entry, which returns the item pointed to by the “cursor.”

■ Next, which moves the “cursor” to the next item and returns that item or, if

there is no next item,

nil.

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