Why can't the form be closed? The magic of revealing VFP object references

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This is our harvest , So that everyone's software can be packaged , More classy , Of course, we also need to get more premium .

Come to Garfield's community , There have been too many fox friends surpassing me , So the next will invite you to share , Listen to their knowledge sharing , Your apple + My apple , In exchange , Or an apple , But knowledge , Your knowledge + My knowledge ＝ Double knowledge .

Many fox friends can't write classes yet , Can't use objects , Let's talk about the basics today . The following example is from the network .

“ Object reference ” The concept of

What is? “ Object reference ” Well ？ such as , Now we have a form form1, There is a page box on the form pageframe1, There is a table on the first page of the page box grid1, Now? , I want to set the title of the first column to “ First column ”, Set the background color to gray , Under normal circumstances , We have to enter long object hierarchies such as ：

thisform.pageframe1.page1.grid1.column1.header1.caption = ” First column “
thisform.pageframe1.page1.grid1.column1.BackColor = RGB(192,192,192)

Use With……EndWith Structure can make the above troublesome input a little easier ：

WITH thisform.pageframe1.page1.grid1.column1
		.header1.caption = " First column "
		.BackColor = RGB(192,192,192)
ENDWITH

Here is the requirement that the code must be continuous , What to do if it is not continuous ？
Put this object into a variable , The variable becomes a part of the object .

LOCAL oColumn ’ Create a pair of tables Column1 References to objects 
oColumn = thisform.pageframe1.page1.grid1.column1
oColumn.header1.caption = ” First column “
oColumn.BackColor = RGB(192,192,192)

Here to create oColumn Variable , Then assign it a value Column1 object , In fact, it is not really assigned , In fact, it's just a point , This object is still in its original position , This object references , such , We can operate directly Column1 Object oColumn The variable .

Yes oColumn Any operation of will be reflected in Column1 On the object .

Object references are not equal to ordinary variables

it seems , This so-called “ Object reference ” Variables are no different from ordinary variables . Let's prove it .

Continue with the previous example , However, it is necessary to put the Local Change it to Public, Then put this code into the form's Init Method to go , Run this form and close it , See what happened .

“ The form cannot be closed ！ Is it a crash ？ Let me press Ctrl+Alt+Del try ……”

“NO！ Don't do that ！”, No crash , It's just that the reference of the object is making trouble . You can open the debugger to see what happened ： stay Local In the window , The variable name of the form is still , Its type is “O”, But its value is already “.NULL.”, in other words ： The form has actually been released . And below oColumn Variables are different , Its type is “O”, Value is “ object ”！

reason ： Anything created in the form Public Variables are not automatically released when the form is released .

Because we will oColumn Object declared as Public 了 , therefore oColumn Object was not released after closing the form .

We can see it from here ： Using the technology of object reference , You can access any object on the form , This is beyond the reach of ordinary variables .

Pass object reference

Let's consider the advantages of object references ： An object reference is a variable , So you can pass it like a normal variable , Including passing it to another form ; meanwhile , Object reference is more than just a variable , It can have its own properties 、 event 、 Method —— This means that you are even free to add as many custom attributes to it as you like ！

Now let's do a wonderful experiment ：
　　1、 Create a form Form1, Put... On the form 3 Textboxes Text1, Text2, Text3、 One Custom object Custom1、 A command button cmdTransObj, In the command button Click Put the following code into the event ：

Do form form2 with this.Custom1
Thisform.Refresh()

2、 Create a schema form Form2( Put the... Of the form WindowType Property is set to “1— Pattern ”), Like form 1 Put it that way 3 Textboxes , Create a custom attribute for the form oFrm1Cust, In the form of
Init Enter the following code in the event ：

PARAMETER oCustom
This.oFrm1Cust = oCustom
WITH this
		.Text1.Value = . oFrm1Cust.parent.Text1.Value
		.Text2.Value = . oFrm1Cust.parent.Text2.Value
		.Text3.Value = . oFrm1Cust.parent.Text3.Value
ENDWITH

3、 stay Form2 Add a command button to the cmdReturn, Put the following code ：

WITH THISFORM
		. oFrm1Cust.parent.Text1.Value = .Text1.Value
		. oFrm1Cust.parent.Text2.Value = .Text2.Value
		. oFrm1Cust.parent.Text3.Value = .Text3.Value
ENDWITH
THISFORM.Release

OK, Now run Form1, Enter some data in each of the three text boxes , Then press the command button . Forms 1 The data on is now transferred to the form 2 In the three text boxes of , Now put the form 2 Change the data inside , Then press the command button CmdReturn, Forms 2 The changes made in are reflected in the form 1 In the ！

You can use this method to easily pass multiple data between forms , And because the data referenced by the object can be modified directly in the called form , You don't even need to return any parameters —— Consider the difficulty of returning an array from a form 、 From one to the other CreateObject( Form class ) Cannot return parameters in the form created by the method of —— You can totally believe ： This is the best magic ！
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