Question

在Panel paint方法中，我想在第一次调用时创建一个TCIFilter，然后在后续调用中重用过滤器。所以这是代码。它只是切换一个表单级变量FFirst。所以这里有一些代码

if FFirst then
  begin
    ...
    filter := TCIFilter.Wrap(TCIFilter.OCClass.filterWithName(NSSTR('CISepiaTone')));
    ...
    filter.retain;
    FFirst := false;
  end;

如果我省略了retain，那么后来对paint方法的调用会在我尝试使用过滤器时抛出异常（无法识别的选择器被发送到实例 - 因为我猜过滤器不再是TCFilter）。

但是过滤器我已经创建了一个全局变量，因此它永远不会超出范围，所以为什么我需要保留？为什么界面会丢失参考？我缺少的东西，这是在OSX上使用XE6，但我认为这同样适用于iOS，tia

编辑：这是所有的代码 - 也许还有别的我做错了。删除表单上的面板和轨迹栏并连接面板.OnPaint和trackbar.OnChange事件

unit Unit3;

interface

uses
  System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
  system.Rtti, FMX.Platform.Mac, FMX.Canvas.Mac, Macapi.CoreGraphics,
  FMX.Types, FMX.Graphics, FMX.Controls, FMX.Forms, FMX.Dialogs, FMX.StdCtrls,
  Macapi.Helpers, MacApi.Foundation, Macapi.QuartzCore,
   MacApi.CocoaTypes, Macapi.ObjectiveC;

type
  TForm3 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Panel1: TPanel;
    TrackBar1: TTrackBar;
    procedure Panel1Paint(Sender: TObject; Canvas: TCanvas;
      const ARect: TRectF);
    procedure FormCreate(Sender: TObject);
    procedure TrackBar1Change(Sender: TObject);
  private
    cgImage : CGImageRef;
    FFirst : Boolean;
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form3: TForm3;

const
     CoreImageFwk = '/System/Library/Frameworks/CoreImage.framework/CoreImage';

implementation

{$R *.fmx}

type
CIFilterClass = interface(NSObjectClass)
    ['{FB4A9CD9-7D60-482D-A0F4-4F78FC6E7E8D}']
    {class} function filterNamesInCategories(categories: NSArray): NSArray; cdecl;
    {class} function filterNamesInCategory(category: NSString): NSArray; cdecl;
    {class} function filterWithImageData(data: NSData; options: NSDictionary): Pointer; cdecl;
    {class} function filterWithImageURL(url: NSURL; options: NSDictionary): Pointer; cdecl;
    {class} function filterWithName(name: NSString): Pointer; cdecl; overload;
    {class} function filterWithName(name: NSString; keysAndValues: Pointer): Pointer; cdecl; overload;
    {class} function localizedDescriptionForFilterName(filterName: NSString): NSString; cdecl;
    {class} function localizedNameForCategory(category: NSString): NSString; cdecl;
    {class} function localizedNameForFilterName(filterName: NSString): NSString; cdecl;
    {class} function localizedReferenceDocumentationForFilterName(filterName: NSString): NSURL; cdecl;
  end;
  CIFilter = interface(NSObject)
    ['{2ACA27E7-D365-4AAC-A474-E72867CDE89A}']
    function apply(apply: CIKernel): CIImage; cdecl; overload;
    function apply(k: CIKernel; arguments: NSArray; options: NSDictionary): CIImage; cdecl; overload;
    function attributes: NSDictionary; cdecl;
    function inputKeys: NSArray; cdecl;
    function isEnabled: Boolean; cdecl;
    function outputKeys: NSArray; cdecl;
    procedure setDefaults; cdecl;
    // I added these 2 methods because they're not in FMX
    procedure setValue(value: pointer; forKey : NSString); cdecl;
    function outputImage : Pointer {CIImage}; cdecl;
  end;
  TCIFilter = class(TOCGenericImport<CIFilterClass, CIFilter>)  end;

procedure TForm3.FormCreate(Sender: TObject);
begin
  Ffirst := true;
end;

var
  fileNameAndPath : Macapi.Foundation.NSURL;
  beginImage, outputImage : CIImage;
  context : CIContext;
  filter : CIFilter;
  pImage : Pointer;
  p : CGPoint;
  r : CGRect;

procedure TForm3.Panel1Paint(Sender: TObject; Canvas: TCanvas;
  const ARect: TRectF);
 var
 d : double;

  function GetCGContextFromCanvas(ACanvas: TCanvas): CGContextRef;
  var
    Context: TRttiContext;
    Field: TRttiField;
  begin
    Field := Context.GetType(ACanvas.ClassType).GetField('FContext');
    Assert(Field <> nil);
    Result := PPointer(Field.GetValue(ACanvas).GetReferenceToRawData)^;
  end;



function kCIContextOutputColorSpace: NSString;
begin
  Result := CocoaNSStringConst(CoreImageFwk, 'kCIContextOutputColorSpace');
end;

begin
  if FFirst then
  begin
    fileNameAndPath := TNSUrl.Wrap(TNSUrl.OCClass.fileURLWithPath(StrToNSStr('/path/to/an/image.png')));

    beginImage := TCIImage.Wrap(TCIImage.OCClass.imageWithContentsOfURL(fileNameAndPath));
    context := TCIContext.Wrap(TCIContext.OCClass.contextWithCGContext( GetCGContextFromCanvas(Canvas), nil ));
    filter := TCIFilter.Wrap(TCIFilter.OCClass.filterWithName(NSSTR('CISepiaTone')));
    filter.setValue( (beginImage as ILocalObject).GetObjectID, NSSTR('inputImage'));
    filter.retain; // comment out this line and it crashes
    context.retain; // same with this one
    FFirst := false;
  end;

  d := TrackBar1.value/100;
  filter.setValue( TNSNumber.OCClass.numberWithFloat(d), NSSTR('inputIntensity'));


   outputImage := TCIImage.Wrap(filter.outputImage);

   cgImage :=  context.createCGImage(outputImage, outputImage.extent);
   p := CGPointMake(0,0);
   r := CGRectMake(0,0, outputImage.extent.size.width, outputImage.extent.size.height);
   CGContextDrawImage(GetCGContextFromCanvas(Canvas), r, cgImage);
   CGImageRelease(cgImage);
end;

procedure TForm3.TrackBar1Change(Sender: TObject);
begin
  Panel1.Repaint;
end;

end.

编辑2：在这里查看基本问题 Delphi XE6 ARC on OSX releasing variables

Answer 1

您必须记住Delphi在您的项目中使用ARC 为了做到这一点，它插入代码以增加和减少适当点的引用计数它仅为需要引用计数的类型（接口，字符串等）插入此代码它不会为其他类型添加此代码;特别是指针。

我强烈怀疑你的问题在这里：

procedure setValue(value: pointer; forKey : NSString); cdecl;

您将对象提供给setValue，但您将其伪装成普通指针这意味着将发生以下情况（我在这里推测，因为您没有包含SetValue的代码）。

您复制在SetValue中传递的对象并将其分配给Filter。（这不会增加引用计数，因为您使用的是普通指针）旧的过滤器由value替换，并且超出范围并被销毁（这应该是这样） Filter现在是SetValue中传递的对象的副本。

同时原始对象超出范围;它的引用数量变为零并且它被破坏了现在Filter指向已销毁的引用。

解决方案
通过将value参数设为refcounted类型或在value.retain内调用SetValue来确保自动引用计数。

我创建了一个过滤器并将其设置为全局变量，为什么我需要保留调用？

1 个答案: