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<TD class="tt2" bgcolor="#F5F8F8" width="84%"><center><B><FONT style="FONT-SIZE: 16.5pt" COLOR="#FF6666" FACE="楷體_GB2312">第二十章 開(kāi)發(fā)Delphi對(duì)象式數(shù)據(jù)管理功能（三）</FONT></B></center>
<hr color="#EE9B73" size="1" width="94%">
<font face="Arial"><p>20.2.1.1 TFiler</font><font face="宋體" lang="ZH-CN">對(duì)象的屬性和方法 </p>
<p> </font><font face="Arial">1. Root</font><font face="宋體" lang="ZH-CN">屬性</p>
<p> 聲明：</font><font face="Arial">property Root: TComponent; </p>
<p>Root </font><font face="宋體" lang="ZH-CN">屬性給</font><font face="Arial">Filer</font><font
face="宋體" lang="ZH-CN">對(duì)象指出被讀寫(xiě)的對(duì)象中哪一個(gè)對(duì)象是根或主要擁有者。</font><font
face="Arial">RootComponent</font><font face="宋體" lang="ZH-CN">和</font><font
face="Arial">WriteRootComponent</font><font face="宋體" lang="ZH-CN">方法在讀和寫(xiě)部件及其擁有的部件前先設(shè)置</font><font
face="Arial">Root</font><font face="宋體" lang="ZH-CN">的值。</p>
<p> </font><font face="Arial">2. Ancestor</font><font face="宋體" lang="ZH-CN">屬性</p>
<p> 聲明：</font><font face="Arial">property Ancestor: TPersistent; </p>
<p>Ancestor</font><font face="宋體" lang="ZH-CN">屬性用于往繼承下來(lái)的窗體中寫(xiě)部件，因?yàn)楫?dāng)寫(xiě)部件時(shí)，</font><font
face="Arial">Write</font><font face="宋體" lang="ZH-CN">對(duì)象只需要寫(xiě)入與所繼承的部件不同的屬性，所以在寫(xiě)之前要跟蹤每個(gè)繼承的部件，并且比較它們的屬性。</p>
<p> 如果</font><font face="Arial">Ancestor</font><font face="宋體" lang="ZH-CN">為</font><font
face="Arial">nil</font><font face="宋體" lang="ZH-CN">，就表示沒(méi)有相應(yīng)的繼承的部件，</font><font
face="Arial">Writer</font><font face="宋體" lang="ZH-CN">對(duì)象應(yīng)當(dāng)將部件完全寫(xiě)入流。</font><font
face="Arial">Ancestor</font><font face="宋體" lang="ZH-CN">一般為</font><font
face="Arial">nil</font><font face="宋體" lang="ZH-CN">，只有當(dāng)調(diào)用</font><font
face="Arial">WriteDescendant</font><font face="宋體" lang="ZH-CN">和</font><font
face="Arial">WriteDescendantRes</font><font face="宋體" lang="ZH-CN">時(shí)，才給賦值。當(dāng)編寫(xiě)和覆蓋</font><font
face="Arial">DefineProperties</font><font face="宋體" lang="ZH-CN">時(shí)，必須設(shè)置</font><font
face="Arial">Ancestor</font><font face="宋體" lang="ZH-CN">的值。</p>
<p> </font><font face="Arial">3. IgnoreChildren</font><font face="宋體"
lang="ZH-CN">屬性</p>
<p> 聲明：</font><font face="Arial">property Ignorechildren: Boolean;</p>
<p>IgnoreChildren</font><font face="宋體" lang="ZH-CN">屬性使一個(gè)</font><font
face="Arial">Writer</font><font face="宋體" lang="ZH-CN">對(duì)象存儲(chǔ)部件時(shí)可以不存儲(chǔ)該部件擁有的部件。如果</font><font
face="Arial">IgnoreChildren</font><font face="宋體" lang="ZH-CN">屬性為</font><font
face="Arial">True</font><font face="宋體" lang="ZH-CN">，則</font><font face="Arial">Writer</font><font
face="宋體" lang="ZH-CN">對(duì)象存儲(chǔ)部件不存它擁有的子部件。否則，</font><font
face="Arial">Writer</font><font face="宋體" lang="ZH-CN">對(duì)象將所有其擁有的對(duì)象寫(xiě)入流。</p>
<p> </font><font face="Arial">4. Create</font><font face="宋體" lang="ZH-CN">方法</p>
<p> 聲明：</font><font face="Arial">constructor Create(Stream: TStream; BufSize:
Cardinal); </p>
<p></font><font face="宋體" lang="ZH-CN"> </font><font face="Arial">Create</font><font
face="宋體" lang="ZH-CN">方法創(chuàng)建一個(gè)新的</font><font face="Arial">Filer</font><font
face="宋體" lang="ZH-CN">對(duì)象，建立它和流</font><font face="Arial">Stream</font><font
face="宋體" lang="ZH-CN">的聯(lián)系；并且給它分配一個(gè)緩沖區(qū)</font><font
face="Arial">Buffer</font><font face="宋體" lang="ZH-CN">。</font><font face="Arial">Buffer</font><font
face="宋體" lang="ZH-CN">的大小由</font><font face="Arial">BufSize</font><font
face="宋體" lang="ZH-CN">指定。</p>
<p> </font><font face="Arial">5. Defineproperty</font><font face="宋體"
lang="ZH-CN">方法</p>
<p> 聲明：</font><font face="Arial">procedure Defineproperty(const Name: String;
ReadData: TReaderProc; </p>
<p>WriteData: TWriterProc; HasData: Boolean); virtual; abstract; </p>
<p>Defineproperty</font><font face="宋體" lang="ZH-CN">方法定義</font><font
face="Arial">Filer</font><font face="宋體" lang="ZH-CN">對(duì)象將作為屬性存儲(chǔ)的數(shù)據(jù)。</font><font
face="Arial">Name</font><font face="宋體" lang="ZH-CN">參數(shù)描述接受的屬性名，該屬性不在</font><font
face="Arial">published</font><font face="宋體" lang="ZH-CN">部分定義。</font><font
face="Arial">ReadData</font><font face="宋體" lang="ZH-CN">和</font><font face="Arial">WriteData</font><font
face="宋體" lang="ZH-CN">參數(shù)指定在存取對(duì)象時(shí)讀和寫(xiě)所需數(shù)據(jù)的方法。</font><font
face="Arial">HasData</font><font face="宋體" lang="ZH-CN">參數(shù)在運(yùn)行時(shí)決定了屬性是否有數(shù)據(jù)要存儲(chǔ)。</p>
<p> 只有當(dāng)對(duì)象有數(shù)據(jù)要存儲(chǔ)時(shí)，才在該對(duì)象的</font><font
face="Arial">DefineProperties</font><font face="宋體" lang="ZH-CN">中調(diào)用</font><font
face="Arial">DefineProperty</font><font face="宋體" lang="ZH-CN">。</font><font
face="Arial">DefineProperties</font><font face="宋體" lang="ZH-CN">有一個(gè)</font><font
face="Arial">Filer</font><font face="宋體" lang="ZH-CN">對(duì)象作為它的參數(shù)，調(diào)用的就是該</font><font
face="Arial">Filer</font><font face="宋體" lang="ZH-CN">對(duì)象的</font><font
face="Arial">DefineProperty</font><font face="宋體" lang="ZH-CN">和</font><font
face="Arial">DefineBinaryProperty</font><font face="宋體" lang="ZH-CN">方法。當(dāng)定義屬性時(shí)，</font><font
face="Arial">Writer</font><font face="宋體" lang="ZH-CN">對(duì)象應(yīng)當(dāng)引用</font><font
face="Arial">Ancestor</font><font face="宋體" lang="ZH-CN">屬性，如果該屬性非空，</font><font
face="Arial">Writer</font><font face="宋體" lang="ZH-CN">對(duì)象應(yīng)當(dāng)只寫(xiě)入與從</font><font
face="Arial">Ancestor</font><font face="宋體" lang="ZH-CN">繼承的不同的屬性的值。</p>
<p> 一個(gè)最簡(jiǎn)單的例子是</font><font face="Arial">TComponent</font><font
face="宋體" lang="ZH-CN">的</font><font face="Arial">DefineProperties</font><font
face="宋體" lang="ZH-CN">方法。盡管</font><font face="Arial">TComponent </font><font
face="宋體" lang="ZH-CN">沒(méi)有在</font><font face="Arial">published</font><font
face="宋體" lang="ZH-CN">中定義</font><font face="Arial">Left</font><font
face="宋體" lang="ZH-CN">、</font><font face="Arial">Top</font><font face="宋體"
lang="ZH-CN">屬性，但該方法存儲(chǔ)了部件的位置信息。</p>
<p> </p>
<p></font><font face="Arial">procedure TComponent.DefineProperties(Filer: TFiler);</p>
<p>begin</p>
<p>Filer.DefineProperty('Left', ReadLeft, WriteLeft, LongRec(FDesignInfo).Lo <> 0);</p>
<p>Filer.DefineProperty('Top', ReadTop, WriteTop, LongRec(FDesignInfo).Hi <> 0);</p>
<p>end;</p>
<p></font> <font face="Arial"></p>
<p>6. DefineBinaryproperty</font><font face="宋體" lang="ZH-CN">方法</p>
<p> 聲明：</font><font face="Arial">procedure DefineBinaryproperty(const Name:
String; </p>
<p>ReadData, WriteData: TStreamProc; </p>
<p>HisData: Boolean); virtual; abstract; </p>
<p>DefineBinaryProperty</font><font face="宋體" lang="ZH-CN">方法定義</font><font
face="Arial">Filer</font><font face="宋體" lang="ZH-CN">對(duì)象作為屬性存儲(chǔ)的二進(jìn)制數(shù)據(jù)。</font><font
face="Arial">Name</font><font face="宋體" lang="ZH-CN">參數(shù)描述屬性名。</font><font
face="Arial">ReadData</font><font face="宋體" lang="ZH-CN">和</font><font face="Arial">WriteData</font><font
face="宋體" lang="ZH-CN">參數(shù)描述所存儲(chǔ)的對(duì)象中讀寫(xiě)所需數(shù)據(jù)的方法。</font><font
face="Arial">HasData</font><font face="宋體" lang="ZH-CN">參數(shù)在運(yùn)行時(shí)決定屬性是否有數(shù)據(jù)要存。</p>
<p> </font><font face="Arial">DefineBinaryProperty</font><font face="宋體"
lang="ZH-CN">和</font><font face="Arial">DefineProperty</font><font face="宋體"
lang="ZH-CN">方法的不同之處在于，二進(jìn)制型的屬性直接用</font><font
face="Arial">Stream</font><font face="宋體" lang="ZH-CN">對(duì)象讀寫(xiě)，而不是通過(guò)</font><font
face="Arial">Filer</font><font face="宋體" lang="ZH-CN">對(duì)象。通過(guò)</font><font
face="Arial">ReadData</font><font face="宋體" lang="ZH-CN">和</font><font face="Arial">WriteData</font><font
face="宋體" lang="ZH-CN">傳入的方法，直接將對(duì)象數(shù)據(jù)寫(xiě)入流或從流讀出。</p>
<p> </font><font face="Arial">DefineBinaryProperty</font><font face="宋體"
lang="ZH-CN">屬性用得較少。只有標(biāo)準(zhǔn)的</font><font face="Arial">VCL</font><font
face="宋體" lang="ZH-CN">對(duì)象定義了象圖形、圖像之類的二進(jìn)制屬性的部件中才用它。</p>
<p> </font><font face="Arial">7. FlushBuffer</font><font face="宋體" lang="ZH-CN">方法</p>
<p> 聲明：</font><font face="Arial">procedure FlushBuffer; virtual: abstract; </p>
<p>FlushBuffer</font><font face="宋體" lang="ZH-CN">方法用于使</font><font
face="Arial">Filer</font><font face="宋體" lang="ZH-CN">對(duì)象的緩沖區(qū)與相聯(lián)的</font><font
face="Arial">Stream</font><font face="宋體" lang="ZH-CN">對(duì)象同步。對(duì)</font><font
face="Arial">Reader</font><font face="宋體" lang="ZH-CN">對(duì)象來(lái)說(shuō)，是通過(guò)重新分配緩沖區(qū)；對(duì)于</font><font
face="Arial">Writer</font><font face="宋體" lang="ZH-CN">對(duì)象是通過(guò)寫(xiě)入當(dāng)前緩沖區(qū)。</p>
<p> </font><font face="Arial">FlushBuffer</font><font face="宋體" lang="ZH-CN">是一個(gè)抽象方法，</font><font
face="Arial">TReader</font><font face="宋體" lang="ZH-CN">和</font><font face="Arial">TWriter</font><font
face="宋體" lang="ZH-CN">都覆蓋了它，提供了具體實(shí)現(xiàn)。</p>
<p> </font><font face="Arial"></p>
<p>20.2.1.2 TFiler</font><font face="宋體" lang="ZH-CN">對(duì)象的實(shí)現(xiàn)原理</p>
<p> </p>
<p> </font><font face="Arial">TFiler</font><font face="宋體" lang="ZH-CN">對(duì)象是</font><font
face="Arial">Filer</font><font face="宋體" lang="ZH-CN">對(duì)象的基礎(chǔ)類，它定義的大多數(shù)方法都是抽象類型的，沒(méi)有具體實(shí)現(xiàn)它，這些方法要在</font><font
face="Arial">TReader</font><font face="宋體" lang="ZH-CN">和</font><font face="Arial">TWrite</font><font
face="宋體" lang="ZH-CN">中覆蓋。但它們提供了</font><font face="Arial">Filer</font><font
face="宋體" lang="ZH-CN">對(duì)象的框架，了解它無(wú)疑是很重要的。</p>
<p> </font><font face="Arial">1. TFiler</font><font face="宋體" lang="ZH-CN">對(duì)象屬性的實(shí)現(xiàn)</p>
<p> </font><font face="Arial">TFiler</font><font face="宋體" lang="ZH-CN">對(duì)象定義了三個(gè)屬性：</font><font
face="Arial">Root</font><font face="宋體" lang="ZH-CN">、</font><font face="Arial">Ancestor</font><font
face="宋體" lang="ZH-CN">和</font><font face="Arial">IgnoreChildren</font><font
face="宋體" lang="ZH-CN">。正如定義對(duì)象屬性通常所采用的方法那樣，要在</font><font
face="Arial">private</font><font face="宋體" lang="ZH-CN">部分定義存儲(chǔ)屬性值的數(shù)據(jù)域，然后在</font><font
face="Arial">public</font><font face="宋體" lang="ZH-CN">或</font><font face="Arial">Published</font><font
face="宋體" lang="ZH-CN">部分定義該屬性，并按需要增加讀寫(xiě)控制。它們的定義如下：</p>
<p> </p>
<p></font><font face="Arial">TFiler = class(TObject)</p>
<p>private</p>
<p></font><font face="宋體" lang="ZH-CN">…</font><font face="Arial"> </p>
<p>FRoot: TComponent;</p>
<p>FAncestor: TPersistent;</p>
<p>FIgnoreChildren: Boolean;</p>
<p>public</p>
<p></font><font face="宋體" lang="ZH-CN">…</p>
<p></font><font face="Arial">property Root: TComponent read FRoot write FRoot;</p>
<p>property Ancestor: TPersistent read FAncestor write FAncestor;</p>
<p>property IgnoreChildren: Boolean read FIgnoreChildren write FIgnoreChildren;</p>
<p>end;</p>
<p></font> <font face="宋體" lang="ZH-CN"></p>
<p> 它們?cè)谧x寫(xiě)控制上都是直接讀寫(xiě)私有的數(shù)據(jù)域。</p>
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