[英]How to extract original JString value from Listbox in Android Kitkat Delphi XE8
I am making a test android multidevice application with Delphi xe8. 我正在用Delphi xe8做一个测试android多设备应用程序。 I am attaching objects to the items in a listbox as follows: 我将对象附加到列表框中的项目,如下所示:
unit Unit1;
interface
uses
System.SysUtils, System.Types, System.UITypes, System.Classes,
System.Variants,
FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics,
Androidapi.JNI.JavaTypes, FMX.Dialogs,
FMX.Controls.Presentation, FMX.StdCtrls, FMX.Layouts, FMX.ListBox,
Androidapi.Helpers;
type
TForm1 = class(TForm)
ListBox1: TListBox;
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.fmx}
//this where I am Attaching objects to items
procedure TForm1.Button1Click(Sender: TObject);
var
str:string;
jstr1:JString;
begin
str:='apple';
jstr1:=StringToJString(str);
ListBox1.Items.AddObject('fruit', TObject(jstr1));
end;
//this where I am extracting the jstring objects
procedure TForm1.Button2Click(Sender: TObject);
var
jstr2:JString;
str2:string;
begin
jstr2:=JString(ListBox1.Items.Objects[i]);
str2:=JStringToString(jstr2);
showmessage('the fruit of the day is '+str2);
end;
end.
The above code run ok and the jstring objects are attached to the items, however, when I want extract the jstring object that has been attached to the item, I do this: 上面的代码运行正常,并且jstring对象已附加到项目中,但是,当我要提取已附加到该项目的jstring对象时,我会这样做:
jstr2:=JString(ListBox1.Items.Objects[i]);
//Above give me an AV: I get incompatible types TObject and JString
str2:=JStringToString(jstr2);
The above code does not compile because of incompatible types TObject and JString. 上面的代码由于类型不兼容的TObject和JString而无法编译。 But yet if had attached a string as the object(instead of a jstring) and wanted to get back those string objects I could just do: 但是,如果将字符串作为对象(而不是jstring)附加并想要取回那些字符串对象,我可以这样做:
str2:=String(ListBox1.Items.Objects[i]);
This would work with regular strings. 这将与常规字符串一起使用。 How do I solve this problem, attach and extract jstring? 如何解决此问题,附加并提取jstring?
This is just a suggestion, and I can not check this (nothing installed here), but you could write a simple object type and store that (I put it in its own unit, which you then use in your form unit): 这只是一个建议,我无法检查(此处未安装任何东西),但是您可以编写一个简单的对象类型并将其存储(我将其放在自己的单元中,然后在表单单元中使用):
unit StringObjs;
interface
uses
Androidapi.JNI.JavaTypes;
type
TStringObj = class
private
FPayload: string;
public
constructor Create(const Payload: JString);
class operator Explicit(const Obj: TStringObj): string;
end;
implementation
uses
Androidapi.Helpers;
constructor TStringObj.Create(const Payload: JString);
begin
FPayload := JStringToString(Payload); // store string, not JString!
end;
class operator TStringObj.Explicit(const Obj: TStringObj): string;
begin
Result := Obj.FPlayload;
end;
end.
And you use it in your form unit's implementation section like: 然后在表单单元的实现部分中使用它,例如:
implementation
uses ..., StringObjs;
...
ListBox1.Items.AddObject('fruit', TStringObj.Create(jstr1));
and reverse: 并反向:
MyString := string(ListBox1.Items[0] as TStringObj);
Note that a form is just a class, but one that the IDE knows about and can edit using the form designer. 请注意,表单只是一类,但是IDE知道并且可以使用表单设计器进行编辑。 To declare other classes, do something similar as I do above. 要声明其他类,请执行与上面类似的操作。 Read the Delphi Language Guide to learn more. 阅读《 Delphi语言指南》以了解更多信息。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.