Reference: https://en.wikipedia.org/wiki/Builder_pattern
Reference 2: My head, sorry for my english
BuilderLabel
BuilderButton
PatternCreator
Builder pattern
Builder pattern is one the most important design pattern in OOP. The main purpose of this pattern is to validate an object before inizializing it, but without checking the object in his class costructor. A builder pattern has also more advantages, that we will see in this tutorial
Inizialize an object
We have different ways to make a new object. Usually we do this:
but if we want to make more than one label, we have to write many lines of code (or use a loop, of course). Another way is to make a costructor:
but at first sight it is difficult to find an error while passing parameters, making the code unreadable.
Make the pattern
To avoid the issues explained previous, we can use a Builder Pattern. Make a new class (I usually call it Builder*, replacing * with our class name).
[ADVANTAGES]
Avoid repetition of names
In c# we can instantiate a new object in this way:
In B4 we need to do this:
Using builder pattern we can do in this way:
Clone object
Each of us would like to be able to do something like this:
but this doesn't make a new copy of the previous label (lb2 is a pointer to previous label, so each change we do in lb2 is done in lb1). Using builder pattern we can do this:
Reference 2: My head, sorry for my english
BuilderLabel
BuilderButton
PatternCreator
Builder pattern
Builder pattern is one the most important design pattern in OOP. The main purpose of this pattern is to validate an object before inizializing it, but without checking the object in his class costructor. A builder pattern has also more advantages, that we will see in this tutorial
Inizialize an object
We have different ways to make a new object. Usually we do this:
B4X:
Dim lb As Label
lb.Initialize("")
lb.SetLayout(0,0,1,1)
lb.Gravity = Gravity.CENTER
lb.Typeface = Typeface.DEFAULT
lb.Textsize = 14
lb.Text = "Some text"
'etc etc
B4X:
Public Sub MakeLabel(Event As String, left As Int, top As Int, width As Int, height As Int, mGravity As Int, mTypeface As Typeface, textsize As Int, text As String) As Label
Dim l As Label
l.Initialize(Event)
l.SetLayout(left,top,width,height)
l.Text = text
l.TextSize = textsize
l.Gravity = mGravity
l.Typeface = mTypeface
Return l
End Sub
Dim lb As Label = MakeLabel("",0,0,1,1,Gravity.CENTER,Typeface.DEFAULT,14,"Some text")Make the pattern
To avoid the issues explained previous, we can use a Builder Pattern. Make a new class (I usually call it Builder*, replacing * with our class name).
B4X:
Sub Class_Globals
Private mSex As Int
Private mAge As Int
Private mName As String
Public const MALE As Int = 0
Public const FEMALE As Int = 1
'You can use type or another class
Type Animal(Name As String, Sex As Int, Age As Int)
End Sub
'Initializes the object. You can add parameters to this method if needed.
Public Sub Initialize As BuilderAnimal
Return Me
End Sub
Public Sub Sex (pSex As Int) As BuilderAnimal
If pSex < 0 Or pSex > 1 Then
Log("Sex error, set male as default")
mSex = MALE
End If
mSex = pSex
Return Me
End Sub
Public Sub Age (pAge As Int) As BuilderAnimal
If pAge < 0 Then
Log("Wrong age!")
mAge = 0
End If
mAge = pAge
Return Me
End Sub
Public Sub Name (pName As String) As BuilderAnimal
mName = pName
Return Me
End Sub
Public Sub Build As Animal
Dim n As Animal
n.Initialize
n.name = mName
n.sex = mSex
Return n
End Sub[ADVANTAGES]
Avoid repetition of names
In c# we can instantiate a new object in this way:
B4X:
TextBlock b = new TextBlock()
{
Margin = new Thickness(0, 0, 0, 0),
MaxHeight = 0,
MaxWidth = 0,
FontSize = 18,
};In B4 we need to do this:
B4X:
Dim dog As Animal
dog.Initialize
dog.Age = 20
dog.Name = "Rex"
dog.Sex = 0Using builder pattern we can do in this way:
B4X:
Dim builder As BuilderAnimal
builder.Initialize _
.Name("Rex") _
.Sex(builder.FEMALE) _
.Age(20)
Dim dog As Animal = builder.BuildClone object
Each of us would like to be able to do something like this:
B4X:
Dim lb as label
lb.initialize("")
'.... ..... .....
dim lb2 as label = lb
lb2.setLayout(0,0,1,1)
B4X:
Dim builder As BuilderAnimal
builder.Initialize _
.Name("Rex") _
.Sex(builder.FEMALE) _
.Age(20)
Dim dog As Animal = builder.Build
Dim cat As Animal = builder.Build
Dim monkey As Animal = builder.Name("Giaquinto").Build
Log(dog)
Log(cat)
Log(monkey)
'Log
'[Age=0, IsInitialized=true, Name=Rex, Sex=1]
'[Age=0, IsInitialized=true, Name=Rex, Sex=1]
'[Age=0, IsInitialized=true, Name=Giaquinto, Sex=1]
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