Question

我今天开始学习课程和对象编程。手册中有代码我必须复制才能运行和保存。我需要创建一个类（TLine）并使用该类来实例化一个对象。

问题：我的RichEdit组件中没有显示输出。我将代码完全从书中复制到delphi，但没有显示输出。

输出应如何显示：＆＃34; **********＆＃34;

我的课程：

<script>
    function checkImageLoad() {
        if (document.getElementById("1st_image").complete == true) {
            console.log("1st_image Loaded!");
        }
        document.getElementById("2nd_image").src = "http://example.org/2nd_image.png";
    }
</script>
<body onload="checkImageLoad();">
<img id="1st_image" src="http://example.org/1st_image.png">
<img id="2nd_image" src="http://example.org/loading_please_wait.gif">

实例化TLine类的Object的代码：

unit Lines_U;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs;

Type
  TLine = Class
Public
  fSize : integer;
  fPattern : char;

public
   Constructor Create;
   Procedure Draw(Var line: string);
end;

implementation

{ TLine }

Constructor TLine.Create;
begin
   fSize := 10;
   fPattern := '*';
end;

Procedure TLine.Draw(Var line: string);
Var
loop : integer;
begin
    for loop := 1 to fSize do
    begin
    line := line + fPattern;
    end;
end;
end.

Answer 1

您的代码未运行的原因是您的事件处理程序Form1.FormCreate未链接到OnCreate事件。恢复对象检查器中的链接。

关于活动处理程序
切勿手动编写事件处理程序（所有以On...开头的程序）。始终使用Object inspector创建它们。

如果您双击一个事件，Delphi将为您创建一个可以填充数据的代码模板确保在对象检查器中填充了事件处理程序。如果不是，他们将无法工作（如你所见）如果您想删除事件处理程序不在对象检查器中将其删除，请将事件处理过程中的代码减少回空模板。
Delphi会看到它是空的并在下一次编译时删除它。

关于您的代码
除了缺少的链接，您的代码没有任何问题。它运行得很好。
虽然有一些风格问题，但这些问题与操作无关，但重要的是它们很重要。

以下是我重写代码的方法。

unit Lines_U;

interface

//only import units that you actually use.    

type  //please type reserved words in all lowercase, this is Pascal not VB.
  TLine = class
  private //make data members private.
    fSize : integer;
    fPattern : char;
  public
    constructor Create;
    procedure Draw(var line: string);
    property Size: integer read fSize write fSize; //Use properties to expose data members.
    property Pattern: char read fPattern write fPattern;   
  end;

implementation

{ TLine }

constructor TLine.Create;
begin
  inherited; //make the inherited call in your constructor explicit.
  fSize := 10;
  fPattern := '*';
end;

procedure TLine.Draw(var line: string);
//var
  //loop : integer; //use consistent indentation 
begin
  //Changing a string ten times in a row is inefficient.
  //try to do your changes all at once.
  //for loop := 1 to fSize do begin
  //  line := line + fPattern;
  //end;
  Line:= Line + StringOfChar(fPattern, fSize); 
end;

end.

您的表格：

unit UseLine_U;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ComCtrls, Lines_U;  
  //put your own unit last, to prevent name clashes with built in classes and functions.


type
  TForm1 = class(TForm)
    //note that the {nothing} line is really **published**. 
    //And data members should be private
    //Line : TLine;  //Line should be private.
    RedOut: TRichEdit;
    procedure FormCreate(Sender: TObject);
  private
    //Prefix all private data with `F` for Field.
    FLine: TLine;  //Line should be a item in the form, not a global var.
  public
    property Line: TLine read FLine; //read only access to line.
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var 
  tempLine : string;
  i: integer;
begin
  //tempLine:= '';  //local variables should be initialized.
  //However strings are always initialized to '', because they are managed types.
  //everything else will contain random data unless you fill it!
  FLine := TLine.Create;
  Line.Draw(tempLine);
  i:= 0;  //init i, otherwise it will be random!
  while i < 5 do begin  //always use `begin-end` in loops, never a naked `do`
    RedOut.Lines.Add(tempLine);
    i:= i + 1;
  end; {while}  //I like to annotate my loop `end`s, but that's just me.
  FreeAndNil(FLine);   //Dispose of TLine when you're done with it.
end;

end.

我可以想到其他事情，但我不想让你超负荷。

为什么没有显示输出？

1 个答案: