<p>SetString(Result, PChar(nil), L);</p>
<p>Read(Pointer(Result)^, L);</p>
<p>end;</p>
<p></font>　<font face="Arial"></p>
<p></font><font face="宋體" lang="ZH-CN">如果</font><font face="Arial">VaString</font><font
face="宋體" lang="ZH-CN">類型緊接著一個字節(jié)存有字符串的長度；如果是</font><font
face="Arial">VaLString</font><font face="宋體" lang="ZH-CN">類，則緊接著兩個字節(jié)存放字符串長度，然后根據(jù)字符串長度用</font><font
face="Arial">SetString</font><font face="宋體" lang="ZH-CN">過程給分配空間，用</font><font
face="Arial">Read</font><font face="宋體" lang="ZH-CN">方法讀出數(shù)據(jù)。</p>
<p>　　</font><font face="Arial">ReadFloat</font><font face="宋體" lang="ZH-CN">方法允許將整型值轉(zhuǎn)換為浮點型。</p>
<p>　</p>
<p></font><font face="Arial">function TReader.ReadFloat: Extended;</p>
<p>begin</p>
<p>if ReadValue = vaExtended then Read(Result, SizeOf(Result)) else</p>
<p>begin</p>
<p>Dec(FBufPos);</font><font face="宋體" lang="ZH-CN"></p>
<p></font><font face="Arial">Result := ReadInteger;</font><font face="宋體" lang="ZH-CN"></p>
<p></font><font face="Arial">end;</p>
<p>end;</p>
<p></font>　<font face="Arial"></p>
<p></font><font face="宋體" lang="ZH-CN">字符類型數(shù)據(jù)設(shè)有直接的標志，它是根據(jù)</font><font
face="Arial">VaString</font><font face="宋體" lang="ZH-CN">后面放一個序值為</font><font
face="Arial">1</font><font face="宋體" lang="ZH-CN">的字節(jié)來判斷的。</p>
<p>　</p>
<p></font><font face="Arial">function TReader.ReadChar: Char;</p>
<p>begin</p>
<p>CheckValue(vaString);</p>
<p>Read(Result, 1);</p>
<p>if Ord(Result) &lt;&gt; 1 then</p>
<p>begin</p>
<p>Dec(FBufPos);</p>
<p>ReadStr;</p>
<p>PropValueError;</p>
<p>end;</p>
<p>Read(Result, 1);</p>
<p>end;</p>
<p></font>　<font face="Arial"></p>
<p></font><font face="宋體" lang="ZH-CN">出于讀取</font><font face="Arial">DFM</font><font
face="宋體" lang="ZH-CN">文件需要，</font><font face="Arial">Filer</font><font
face="宋體" lang="ZH-CN">對象支持讀取標識符。</p>
<p>　</p>
<p></font><font face="Arial">function TReader.ReadIdent: string;</p>
<p>var</p>
<p>L: Byte;</p>
<p>begin</p>
<p>case ReadValue of</p>
<p>vaIdent:</p>
<p>begin</p>
<p>Read(L, SizeOf(Byte));</p>
<p>SetString(Result, PChar(nil), L);</p>
<p>Read(Result[1], L);</p>
<p>end;</p>
<p>vaFalse:</p>
<p>Result := 'False';</p>
<p>vaTrue:</p>
<p>Result := 'True';</p>
<p>vaNil:</p>
<p>Result := 'nil';</p>
<p>else</p>
<p>PropValueError;</p>
<p>end;</p>
<p>end;</p>
<p></font>　<font face="Arial"></p>
<p></font><font face="宋體" lang="ZH-CN">一般說來，各種復(fù)雜的數(shù)據(jù)結(jié)構(gòu)都是由這些簡單數(shù)據(jù)組成</font><font
face="Arial">;</font><font face="宋體" lang="ZH-CN">定義了這些方法等于給讀各種類型的數(shù)據(jù)提供了元操作，使用很方便。例如，讀取字符串類型的數(shù)據(jù)時，如果采用傳流方法還要判斷字符串的長度，使用</font><font
face="Arial">ReadString</font><font face="宋體" lang="ZH-CN">方法就不同了。但應(yīng)該特別注意的是這些類型數(shù)據(jù)的存儲格式是由</font><font
face="Arial">Delphi</font><font face="宋體" lang="ZH-CN">設(shè)計的與簡單數(shù)據(jù)類型有明顯的不同。因此，存入數(shù)據(jù)時應(yīng)當使用</font><font
face="Arial">Writer</font><font face="宋體" lang="ZH-CN">對象相應(yīng)的方法，而且在讀數(shù)據(jù)前要用</font><font
face="Arial">NextValue</font><font face="宋體" lang="ZH-CN">方法進行判斷，否則會觸發(fā)異常事件。</p>
<p>　　</font><font face="Arial">6. </font><font face="宋體" lang="ZH-CN">讀取部件的方法的實現(xiàn)</p>
<p>　　</font><font face="Arial">Reader</font><font face="宋體" lang="ZH-CN">對象中用于讀取部件的方法有</font><font
face="Arial">ReadSignature</font><font face="宋體" lang="ZH-CN">、</font><font
face="Arial">ReadPrefix</font><font face="宋體" lang="ZH-CN">、</font><font
face="Arial">ReadComponent</font><font face="宋體" lang="ZH-CN">、</font><font
face="Arial">ReadRootComponent</font><font face="宋體" lang="ZH-CN">和</font><font
face="Arial">ReadComponents</font><font face="宋體" lang="ZH-CN">。</font><font
face="Arial"></p>
<p>ReadSignature</font><font face="宋體" lang="ZH-CN">方法主要用于讀取</font><font
face="Arial">Delphi Filer</font><font face="宋體" lang="ZH-CN">對象標簽一般在讀取部件前，都要用調(diào)用</font><font
face="Arial">ReadSignature</font><font face="宋體" lang="ZH-CN">方法以指導部件讀寫過程。</p>
<p>　</p>
<p></font><font face="Arial">procedure TReader.ReadSignature;</p>
<p>var</p>
<p>Signature: Longint;</p>
<p>begin</p>
<p>Read(Signature, SizeOf(Signature));</p>
<p>if Signature &lt;&gt; Longint(FilerSignature) then ReadError(SInvalidImage);</p>
<p>end;</p>
<p></font>　<font face="Arial"></p>
<p>FilerSignature</font><font face="宋體" lang="ZH-CN">就是</font><font face="Arial">Filer</font><font
face="宋體" lang="ZH-CN">對象標簽其值為“</font><font face="Arial">TPF0</font><font
face="宋體" lang="ZH-CN">”</font><font face="Arial"> </font><font face="宋體"
lang="ZH-CN">，如果讀的不是“</font><font face="Arial">TPF0</font><font
face="宋體" lang="ZH-CN">”</font><font face="Arial"> </font><font face="宋體"
lang="ZH-CN">，則會觸發(fā)</font><font face="Arial">SInValidImage</font><font
face="宋體" lang="ZH-CN">異常事件。</p>
<p>　　</font><font face="Arial">ReadPrefix</font><font face="宋體" lang="ZH-CN">方法是用于讀取流中部件前的標志位，該標志表示該部件是否處于從祖先窗體中繼承的窗體中和它在窗體中的位置是否很重要。</p>
<p>　</p>
<p></font><font face="Arial">procedure TReader.ReadPrefix(var Flags: TFilerFlags; var
AChildPos: Integer);</p>
<p>var</p>
<p>Prefix: Byte;</p>
<p>begin</p>
<p>Flags := [];</p>
<p>if Byte(NextValue) and $F0 = $F0 then</p>
<p>begin</p>
<p>Prefix := Byte(ReadValue);</p>
<p>Byte(Flags) := Prefix and $0F;</p>
<p>if ffChildPos in Flags then AChildPos := ReadInteger;</p>
<p>end;</p>
<p>end;</p>
<p></font>　<font face="宋體" lang="ZH-CN"></p>
<p>　　</font><font face="Arial">TFilerFlags</font><font face="宋體" lang="ZH-CN">的定義是這樣的：</p>
<p>　</p>
<p>　　　</font><font face="Arial">TFilerFlag = (ffInherited, ffChildPos); </p>
<p>TFilerFlags = Set of TFilerFlag; </p>
<p></font>　<font face="Arial"></p>
<p></font><font face="宋體" lang="ZH-CN">充當標志的字節(jié)的高四位是</font><font
face="Arial">$F</font><font face="宋體" lang="ZH-CN">，低四位是集合的值，也是標志位的真正含義。如果</font><font
face="Arial">ffChildPos</font><font face="宋體" lang="ZH-CN">置位，則緊接著的整型數(shù)字中放著部件在窗體中的位置序值。</p>
<p>　　</font><font face="Arial">ReadComponent</font><font face="宋體" lang="ZH-CN">方法用于從</font><font
face="Arial">Reader</font><font face="宋體" lang="ZH-CN">對象的流中讀取部件。</font><font
face="Arial">Component </font><font face="宋體" lang="ZH-CN">參數(shù)指定了要從流中讀取的對象。函數(shù)返回所讀的部件。</p>
<p>　</p>
<p></font><font face="Arial">function TReader.ReadComponent(Component: TComponent):
TComponent;</p>
<p>var</p>
<p>CompClass, CompName: string;</p>
<p>Flags: TFilerFlags;</p>
<p>Position: Integer;</p>
<p></font><font face="宋體" lang="ZH-CN">…</p>
<p>　</p>
<p></font><font face="Arial">begin</p>
<p>ReadPrefix(Flags, Position);</p>
<p>CompClass := ReadStr;</font><font face="宋體" lang="ZH-CN"></p>
<p></font><font face="Arial">CompName := ReadStr;</font><font face="宋體" lang="ZH-CN"></p>
<p></font><font face="Arial">Result := Component;</p>
<p>if Result = nil then</p>
<p>if ffInherited in Flags then</p>
<p>FindExistingComponent else</p>
<p>CreateComponent;</p>
<p>if Result &lt;&gt; nil then</p>
<p>try</p>
<p>Include(Result.FComponentState, csLoading);</p>
<p>if not (ffInherited in Flags) then SetCompName;</p>
<p>if Result = nil then Exit;</p>
<p>Include(Result.FComponentState, csReading);</p>
<p>Result.ReadState(Self);</p>
<p>Exclude(Result.FComponentState, csReading);</p>
<p>if ffChildPos in Flags then Parent.SetChildOrder(Result, Position);</p>
<p>FLoaded.Add(Result);</p>
<p>except</p>
<p>if ComponentCreated then Result.Free;</p>
<p>raise;</p>
<p>end;</p>
<p>end;</p>
<p></font>　<font face="Arial"></p>
<p>ReadCompontent</font><font face="宋體" lang="ZH-CN">方法首先調(diào)用</font><font
face="Arial">ReadPrefix</font><font face="宋體" lang="ZH-CN">方法，讀出部件標志位和它的創(chuàng)建次序值</font><font
face="Arial">(Create Order)</font><font face="宋體" lang="ZH-CN">。然后用</font><font
face="Arial">ReadStr</font><font face="宋體" lang="ZH-CN">方法分別讀出部件類名和部件名。如果</font><font
face="Arial">Component</font><font face="宋體" lang="ZH-CN">參數(shù)為</font><font
face="Arial">nil</font><font face="宋體" lang="ZH-CN">，則執(zhí)行兩個任務(wù)：</font><font
face="Arial"></p>
<p></font><font face="宋體" lang="ZH-CN">●</font><font face="Arial"> </font><font
face="宋體" lang="ZH-CN">如果</font><font face="Arial">ffInberited </font><font
face="宋體" lang="ZH-CN">置位則從</font><font face="Arial">Root </font><font
face="宋體" lang="ZH-CN">找已有部件，否則，就從系統(tǒng)的</font><font
face="Arial">Class</font><font face="宋體" lang="ZH-CN">表中找到該部件類型的定義并創(chuàng)建</font><font
face="Arial"></p>
<p></font><font face="宋體" lang="ZH-CN">●</font><font face="Arial"> </font><font
face="宋體" lang="ZH-CN">如果結(jié)果不為空，將用部件的</font><font
face="Arial">ReadState</font><font face="宋體" lang="ZH-CN">方法讀入各種屬性值，并設(shè)置部件的</font><font
face="Arial">Parent </font><font face="宋體" lang="ZH-CN">屬性，并恢復(fù)它在</font><font
face="Arial">Parent</font><font face="宋體" lang="ZH-CN">部件的創(chuàng)建次序。</p>
<p>　</p>
<p>　　</font><font face="Arial">ReadComponent</font><font face="宋體" lang="ZH-CN">方法主要是調(diào)用</font><font
face="Arial">ReadComponent</font><font face="宋體" lang="ZH-CN">方法從</font><font
face="Arial">Reader</font><font face="宋體" lang="ZH-CN">對象的流中讀取一連串相關(guān)聯(lián)的部件，并分解相互引用關(guān)系。</p>
<p>　</p>
<p></font><font face="Arial">procedure TReader.ReadComponents(AOwner, AParent: TComponent;</p>
<p>Proc: TReadComponentsProc);</p>
<p>var</p>
<p>Component: TComponent;</p>
<p>begin</p>
<p>Root := AOwner;</p>
<p>Owner := AOwner;</p>
<p>Parent := AParent;</p>
<p>BeginReferences;</p>
<p>try</p>
<p>while not EndOfList do</p>