C# 将接口作为参数传递给类构造函数

我正在使用iText7读取PDF文件数据，并根据它们在PDF文件中的位置创建一个xml文件。 我的问题是

iText7程序集中有一个类

LocationTextExtractionStrategy

，如下所示

public class LocationTextExtractionStrategy : ITextExtractionStrategy, IEventListener
{
    public LocationTextExtractionStrategy(ITextChunkLocationStrategy strat);
    public virtual void EventOccurred(IEventData data, EventType type);

    public interface ITextChunkLocationStrategy
    {
        ITextChunkLocation CreateLocation(TextRenderInfo renderInfo, LineSegment baseline);
    }
}

public class TextLocationExtractionStrategy : LocationTextExtractionStrategy
{
    ITextChunkLocationStrategy locationstrategy ;
    public TextLocationExtractionStrategy(ITextChunkLocationStrategy strategy)
    {
        locationstrategy = strategy;
    }

    public override void EventOccurred(IEventData data, EventType type)
    {
        if (!type.Equals(EventType.RENDER_TEXT))
            return;

        TextRenderInfo renderInfo = (TextRenderInfo)data;

        string curFont = renderInfo.GetFont().GetFontProgram().ToString();

        float curFontSize = renderInfo.GetFontSize();

        IList<TextRenderInfo> text = renderInfo.GetCharacterRenderInfos();
        foreach (TextRenderInfo t in text)
        {
            LineSegment lineSegment = t.GetBaseline();
            string letter = t.GetText();
            Vector letterStart = t.GetBaseline().GetStartPoint();
            Vector letterEnd = t.GetAscentLine().GetEndPoint();
            Rectangle letterRect = new Rectangle(letterStart.Get(0), letterStart.Get(1),
                letterEnd.Get(0) - letterStart.Get(0), letterEnd.Get(1) - letterStart.Get(1));

            if (letter != " " && !letter.Contains(' '))
            {
                ITextChunkLocation loc = locationstrategy.CreateLocation(t, lineSegment);
                UTextChunk chunk = new UTextChunk(t, t.GetText(), loc);
                t.GetText();
                t.GetBaseline().GetBoundingRectangle();

                m_locationResult.Add(chunk);
            }
        }
    }
}

现在我将这个类继承到我的项目类中，如下所示

public class LocationTextExtractionStrategy : ITextExtractionStrategy, IEventListener
{
    public LocationTextExtractionStrategy(ITextChunkLocationStrategy strat);
    public virtual void EventOccurred(IEventData data, EventType type);

    public interface ITextChunkLocationStrategy
    {
        ITextChunkLocation CreateLocation(TextRenderInfo renderInfo, LineSegment baseline);
    }
}

public class TextLocationExtractionStrategy : LocationTextExtractionStrategy
{
    ITextChunkLocationStrategy locationstrategy ;
    public TextLocationExtractionStrategy(ITextChunkLocationStrategy strategy)
    {
        locationstrategy = strategy;
    }

    public override void EventOccurred(IEventData data, EventType type)
    {
        if (!type.Equals(EventType.RENDER_TEXT))
            return;

        TextRenderInfo renderInfo = (TextRenderInfo)data;

        string curFont = renderInfo.GetFont().GetFontProgram().ToString();

        float curFontSize = renderInfo.GetFontSize();

        IList<TextRenderInfo> text = renderInfo.GetCharacterRenderInfos();
        foreach (TextRenderInfo t in text)
        {
            LineSegment lineSegment = t.GetBaseline();
            string letter = t.GetText();
            Vector letterStart = t.GetBaseline().GetStartPoint();
            Vector letterEnd = t.GetAscentLine().GetEndPoint();
            Rectangle letterRect = new Rectangle(letterStart.Get(0), letterStart.Get(1),
                letterEnd.Get(0) - letterStart.Get(0), letterEnd.Get(1) - letterStart.Get(1));

            if (letter != " " && !letter.Contains(' '))
            {
                ITextChunkLocation loc = locationstrategy.CreateLocation(t, lineSegment);
                UTextChunk chunk = new UTextChunk(t, t.GetText(), loc);
                t.GetText();
                t.GetBaseline().GetBoundingRectangle();

                m_locationResult.Add(chunk);
            }
        }
    }
}

由于我们不能创建接口的实例，我不知道如何将值传递给接口类型的参数。在上面的几行中，我只是将其赋值为null并调用构造函数，但是如果将null值赋值给它，它会说“对象引用未设置为对象的实例”

你能帮我解决这个问题吗

---

如果在提出我的问题时有任何问题，请告诉我或纠正我。

如果您查看基类的源代码

LocationTextExtractionStrategy

（它是开源的，所以请查看源代码！），您将看到它不仅具有带

ITextChunkLocationStrategy

参数的构造函数，它也有一个没有参数的构造函数

该构造函数实际实例化了该接口的实现，并将其转发给您引用的同一个构造函数：

public LocationTextExtractionStrategy()
    : this(new _ITextChunkLocationStrategy_85()) {
}

private sealed class _ITextChunkLocationStrategy_85 : LocationTextExtractionStrategy.ITextChunkLocationStrategy {
    public _ITextChunkLocationStrategy_85() {
    }

    public ITextChunkLocation CreateLocation(TextRenderInfo renderInfo, LineSegment baseline) {
        return new TextChunkLocationDefaultImp(baseline.GetStartPoint(), baseline.GetEndPoint(), renderInfo.GetSingleSpaceWidth());
    }
}

由于您希望使用

ITextChunkLocationStrategy

实现，而基类不为其提供getter，因此不能简单地使用没有参数的另一个构造函数。您不能实例化这个

\u ITextChunkLocationStrategy\u 85

类，因为它是私有的。您不能简单地将

\u ITextChunkLocationStrategy\u 85

复制到您的代码中，因为

TextChunkLocationDefaultImp

是

内部的

但是，您可以做的是将
TextChunkLocationDefaultImp
复制到您的代码中，然后将
\u ITextChunkLocationStrategy\u 85
复制到您的代码中，使用该类的副本替换基类中使用的
TextChunkLocationDefaultImp
，然后实例化
\u ITextChunkLocationStrategy\u 85
类的副本，以最终获得
ITextChunkLocationStrategy
实现实例

或者，你可以试着进行反思和内省。不过，这可能会导致维护问题

如果一个库提供了泛化某个东西的方法，然后隐藏了它的默认实现，那么这将是一个真正的麻烦


作为参考，
TextChunkLocationDefaultImp
当前的实现如下

internal class TextChunkLocationDefaultImp : ITextChunkLocation {
    private const float DIACRITICAL_MARKS_ALLOWED_VERTICAL_DEVIATION = 2;

    /// <summary>the starting location of the chunk</summary>
    private readonly Vector startLocation;

    /// <summary>the ending location of the chunk</summary>
    private readonly Vector endLocation;

    /// <summary>unit vector in the orientation of the chunk</summary>
    private readonly Vector orientationVector;

    /// <summary>the orientation as a scalar for quick sorting</summary>
    private readonly int orientationMagnitude;

    /// <summary>perpendicular distance to the orientation unit vector (i.e.</summary>
    /// <remarks>
    /// perpendicular distance to the orientation unit vector (i.e. the Y position in an unrotated coordinate system)
    /// we round to the nearest integer to handle the fuzziness of comparing floats
    /// </remarks>
    private readonly int distPerpendicular;

    /// <summary>distance of the start of the chunk parallel to the orientation unit vector (i.e.</summary>
    /// <remarks>distance of the start of the chunk parallel to the orientation unit vector (i.e. the X position in an unrotated coordinate system)
    ///     </remarks>
    private readonly float distParallelStart;

    /// <summary>distance of the end of the chunk parallel to the orientation unit vector (i.e.</summary>
    /// <remarks>distance of the end of the chunk parallel to the orientation unit vector (i.e. the X position in an unrotated coordinate system)
    ///     </remarks>
    private readonly float distParallelEnd;

    /// <summary>the width of a single space character in the font of the chunk</summary>
    private readonly float charSpaceWidth;

    public TextChunkLocationDefaultImp(Vector startLocation, Vector endLocation, float charSpaceWidth) {
        this.startLocation = startLocation;
        this.endLocation = endLocation;
        this.charSpaceWidth = charSpaceWidth;
        Vector oVector = endLocation.Subtract(startLocation);
        if (oVector.Length() == 0) {
            oVector = new Vector(1, 0, 0);
        }
        orientationVector = oVector.Normalize();
        orientationMagnitude = (int)(Math.Atan2(orientationVector.Get(Vector.I2), orientationVector.Get(Vector.I1)
            ) * 1000);
        // see http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
        // the two vectors we are crossing are in the same plane, so the result will be purely
        // in the z-axis (out of plane) direction, so we just take the I3 component of the result
        Vector origin = new Vector(0, 0, 1);
        distPerpendicular = (int)(startLocation.Subtract(origin)).Cross(orientationVector).Get(Vector.I3);
        distParallelStart = orientationVector.Dot(startLocation);
        distParallelEnd = orientationVector.Dot(endLocation);
    }

    public virtual int OrientationMagnitude() {
        return orientationMagnitude;
    }

    public virtual int DistPerpendicular() {
        return distPerpendicular;
    }

    public virtual float DistParallelStart() {
        return distParallelStart;
    }

    public virtual float DistParallelEnd() {
        return distParallelEnd;
    }

    /// <returns>the start location of the text</returns>
    public virtual Vector GetStartLocation() {
        return startLocation;
    }

    /// <returns>the end location of the text</returns>
    public virtual Vector GetEndLocation() {
        return endLocation;
    }

    /// <returns>the width of a single space character as rendered by this chunk</returns>
    public virtual float GetCharSpaceWidth() {
        return charSpaceWidth;
    }

    /// <param name="as">the location to compare to</param>
    /// <returns>true is this location is on the the same line as the other</returns>
    public virtual bool SameLine(ITextChunkLocation @as) {
        if (OrientationMagnitude() != @as.OrientationMagnitude()) {
            return false;
        }
        float distPerpendicularDiff = DistPerpendicular() - @as.DistPerpendicular();
        if (distPerpendicularDiff == 0) {
            return true;
        }
        LineSegment mySegment = new LineSegment(startLocation, endLocation);
        LineSegment otherSegment = new LineSegment(@as.GetStartLocation(), @as.GetEndLocation());
        return Math.Abs(distPerpendicularDiff) <= DIACRITICAL_MARKS_ALLOWED_VERTICAL_DEVIATION && (mySegment.GetLength
            () == 0 || otherSegment.GetLength() == 0);
    }

    /// <summary>
    /// Computes the distance between the end of 'other' and the beginning of this chunk
    /// in the direction of this chunk's orientation vector.
    /// </summary>
    /// <remarks>
    /// Computes the distance between the end of 'other' and the beginning of this chunk
    /// in the direction of this chunk's orientation vector.  Note that it's a bad idea
    /// to call this for chunks that aren't on the same line and orientation, but we don't
    /// explicitly check for that condition for performance reasons.
    /// </remarks>
    /// <param name="other"/>
    /// <returns>the number of spaces between the end of 'other' and the beginning of this chunk</returns>
    public virtual float DistanceFromEndOf(ITextChunkLocation other) {
        return DistParallelStart() - other.DistParallelEnd();
    }

    public virtual bool IsAtWordBoundary(ITextChunkLocation previous) {
        // In case a text chunk is of zero length, this probably means this is a mark character,
        // and we do not actually want to insert a space in such case
        if (startLocation.Equals(endLocation) || previous.GetEndLocation().Equals(previous.GetStartLocation())) {
            return false;
        }
        float dist = DistanceFromEndOf(previous);
        if (dist < 0) {
            dist = previous.DistanceFromEndOf(this);
            //The situation when the chunks intersect. We don't need to add space in this case
            if (dist < 0) {
                return false;
            }
        }
        return dist > GetCharSpaceWidth() / 2.0f;
    }

    internal static bool ContainsMark(ITextChunkLocation baseLocation, ITextChunkLocation markLocation) {
        return baseLocation.GetStartLocation().Get(Vector.I1) <= markLocation.GetStartLocation().Get(Vector.I1) &&
             baseLocation.GetEndLocation().Get(Vector.I1) >= markLocation.GetEndLocation().Get(Vector.I1) && Math.
            Abs(baseLocation.DistPerpendicular() - markLocation.DistPerpendicular()) <= DIACRITICAL_MARKS_ALLOWED_VERTICAL_DEVIATION;
    }
}

内部类TextChunkLocationDefaultImp:ITextChunkLocation{
私有常量浮点变音符号允许的垂直偏差=2；
///块的起始位置
私有只读向量定位；
///块的结束位置
专用只读向量结束位置；
///块方向上的单位向量
私有只读向量方向向量；
///用于快速排序的标量方向
私有只读int方向大小；
///与方向单位向量的垂直距离（即。
/// 
///与方向单位向量的垂直距离（即未旋转坐标系中的Y位置）
///我们四舍五入到最接近的整数来处理比较浮点数的模糊性
/// 
私有只读int；
///平行于方向单位向量的块起点距离（即。
///平行于方向单位向量的块起点距离（即未旋转坐标系中的X位置）
///     
私有只读浮点启动；
///平行于方向单位向量的块端距离（即。
///平行于方向单位向量的块端距离（即未旋转坐标系中的X位置）
///     
私有只读浮点数；
///块字体中单个空格字符的宽度
私有只读浮点字符空间宽度；
public TextChunkLocationDefaultImp（向量位置、向量结束位置、浮点字符空间宽度）{
this.startolocation=startolocation；
this.endLocation=endLocation；
this.charSpaceWidth=charSpaceWidth；
向量向量向量=结束位置。减去（起始位置）；
如果（oVector.Length（）==0）{
oVector=新向量（1,0,0）；
}
方向向量=oVector.Normalize（）；
orientationmagnity=（int）（Math.Atan2（orientationVector.Get（Vector.I2），orientationVector.Get（Vector.I1）
) * 1000);
//看http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
//我们相交的两个向量在同一个平面上，因此结果将完全相同
//在z轴（平面外）方向，我们只取结果的I3分量
向量原点=新向量（0,0,1）；
distvertical=（int）（起始位置。减去（原点））。交叉（方向向量）。获取（向量。I3）；
distParallelStart=方向向量.Dot（位置）；
distParallelEnd=方向向量.Dot（endLocation）；
}
公共虚拟int方向重要性（）{
返回方向大小；
}
公共虚拟整数（）{
返回垂直；
}
公共虚拟浮点数开始（）{
返回并启动；
}
公共虚拟浮点数（）{
返回端；
}
///文本的起始位置
公共虚拟向量{
返回定位；
}
///文本的结束位置
公共虚拟向量GetEndLocation（）{
返回端定位；
}
///此块渲染的单个空格字符的宽度
公共虚拟浮点GetCharSpaceWidth（）{
返回字符空间宽度；
}
///指向com的位置