143 lines
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143 lines
10 KiB
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<title>Serialization Callbacks</title>
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<span class="productTitle">Json.NET - Quick Starts & API Documentation</span><br />
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<span class="topicTitle">Serialization Callbacks</span></div>
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<div id="content">
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<span style="color: DarkGray"> </span>
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<p>Json.NET supports serialization callback methods. A callback can be used to
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manipulate an object before and after its serialization and deserialization by
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the JsonSerializer.</p>
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<ul>
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<li><b>OnSerializing</b></li>
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<li><b>OnSerialized</b></li>
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<li><b>OnDeserializing</b></li>
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<li><b>OnDeserialized</b></li>
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</ul>
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<p>To tell the serializer which methods should be called during the object's serialization
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lifecycle, decorate a method with the appropraite attribute (<a
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href="http://msdn.microsoft.com/en-us/library/system.runtime.serialization.onserializingattribute.aspx" target="_blank">OnSerializingAttribute</a>,
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<a href="http://msdn.microsoft.com/en-us/library/system.runtime.serialization.onserializedattribute.aspx" target="_blank">OnSerializedAttribute</a>,
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<a href="http://msdn.microsoft.com/en-us/library/system.runtime.serialization.ondeserializingattribute.aspx" target="_blank">OnDeserializingAttribute</a>,
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<a href="http://msdn.microsoft.com/en-us/library/system.runtime.serialization.ondeserializedattribute.aspx" target="_blank">OnDeserializedAttribute</a>).</p>
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<p>Example object with serialization callback methods:</p>
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<div class="overflowpanel"> <div class="code">
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<div style="font-family: Courier New; font-size: 10pt; color: black;">
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<pre style="margin: 0px;"><span style="color: blue;">public</span> <span style="color: blue;">class</span> <span style="color: #2b91af;">SerializationEventTestObject</span></pre>
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<pre style="margin: 0px;">{</pre>
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<pre style="margin: 0px;"> <span style="color: green;">// This member is serialized and deserialized with no change.</span></pre>
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<pre style="margin: 0px;"> <span style="color: blue;">public</span> <span style="color: blue;">int</span> Member1 { <span style="color: blue;">get</span>; <span style="color: blue;">set</span>; }</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"> <span style="color: green;">// The value of this field is set and reset during and </span></pre>
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<pre style="margin: 0px;"> <span style="color: green;">// after serialization.</span></pre>
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<pre style="margin: 0px;"> <span style="color: blue;">public</span> <span style="color: blue;">string</span> Member2 { <span style="color: blue;">get</span>; <span style="color: blue;">set</span>; }</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"> <span style="color: green;">// This field is not serialized. The OnDeserializedAttribute </span></pre>
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<pre style="margin: 0px;"> <span style="color: green;">// is used to set the member value after serialization.</span></pre>
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<pre style="margin: 0px;"> [<span style="color: #2b91af;">JsonIgnore</span>]</pre>
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<pre style="margin: 0px;"> <span style="color: blue;">public</span> <span style="color: blue;">string</span> Member3 { <span style="color: blue;">get</span>; <span style="color: blue;">set</span>; }</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"> <span style="color: green;">// This field is set to null, but populated after deserialization.</span></pre>
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<pre style="margin: 0px;"> <span style="color: blue;">public</span> <span style="color: blue;">string</span> Member4 { <span style="color: blue;">get</span>; <span style="color: blue;">set</span>; }</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"> <span style="color: blue;">public</span> SerializationEventTestObject()</pre>
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<pre style="margin: 0px;"> {</pre>
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<pre style="margin: 0px;"> Member1 = 11;</pre>
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<pre style="margin: 0px;"> Member2 = <span style="color: #a31515;">"Hello World!"</span>;</pre>
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<pre style="margin: 0px;"> Member3 = <span style="color: #a31515;">"This is a nonserialized value"</span>;</pre>
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<pre style="margin: 0px;"> Member4 = <span style="color: blue;">null</span>;</pre>
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<pre style="margin: 0px;"> }</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"> [<span style="color: #2b91af;">OnSerializing</span>]</pre>
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<pre style="margin: 0px;"> <span style="color: blue;">internal</span> <span style="color: blue;">void</span> OnSerializingMethod(<span style="color: #2b91af;">StreamingContext</span> context)</pre>
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<pre style="margin: 0px;"> {</pre>
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<pre style="margin: 0px;"> Member2 = <span style="color: #a31515;">"This value went into the data file during serialization."</span>;</pre>
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<pre style="margin: 0px;"> }</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"> [<span style="color: #2b91af;">OnSerialized</span>]</pre>
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<pre style="margin: 0px;"> <span style="color: blue;">internal</span> <span style="color: blue;">void</span> OnSerializedMethod(<span style="color: #2b91af;">StreamingContext</span> context)</pre>
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<pre style="margin: 0px;"> {</pre>
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<pre style="margin: 0px;"> Member2 = <span style="color: #a31515;">"This value was reset after serialization."</span>;</pre>
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<pre style="margin: 0px;"> }</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"> [<span style="color: #2b91af;">OnDeserializing</span>]</pre>
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<pre style="margin: 0px;"> <span style="color: blue;">internal</span> <span style="color: blue;">void</span> OnDeserializingMethod(<span style="color: #2b91af;">StreamingContext</span> context)</pre>
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<pre style="margin: 0px;"> {</pre>
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<pre style="margin: 0px;"> Member3 = <span style="color: #a31515;">"This value was set during deserialization"</span>;</pre>
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<pre style="margin: 0px;"> }</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"> [<span style="color: #2b91af;">OnDeserialized</span>]</pre>
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<pre style="margin: 0px;"> <span style="color: blue;">internal</span> <span style="color: blue;">void</span> OnDeserializedMethod(<span style="color: #2b91af;">StreamingContext</span> context)</pre>
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<pre style="margin: 0px;"> {</pre>
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<pre style="margin: 0px;"> Member4 = <span style="color: #a31515;">"This value was set after deserialization."</span>;</pre>
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<pre style="margin: 0px;"> }</pre>
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<pre style="margin: 0px;">}</pre>
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</div>
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</div></div>
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<p>The example object being serialized and deserialized by Json.NET:</p>
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<div class="overflowpanel"> <div class="code">
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<div style="font-family: Courier New; font-size: 10pt; color: black;">
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<pre style="margin: 0px;"><span style="color: #2b91af;">SerializationEventTestObject</span> obj = <span style="color: blue;">new</span> <span style="color: #2b91af;">SerializationEventTestObject</span>();</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member1);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// 11</span></pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member2);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// Hello World!</span></pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member3);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// This is a nonserialized value</span></pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member4);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// null</span></pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"><span style="color: blue;">string</span> json = <span style="color: #2b91af;">JsonConvert</span>.SerializeObject(obj, <span style="color: #2b91af;">Formatting</span>.Indented);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// {</span></pre>
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<pre style="margin: 0px;"><span style="color: green;">// "Member1": 11,</span></pre>
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<pre style="margin: 0px;"><span style="color: green;">// "Member2": "This value went into the data file during serialization.",</span></pre>
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<pre style="margin: 0px;"><span style="color: green;">// "Member4": null</span></pre>
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<pre style="margin: 0px;"><span style="color: green;">// }</span></pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member1);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// 11</span></pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member2);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// This value was reset after serialization.</span></pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member3);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// This is a nonserialized value</span></pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member4);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// null</span></pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;">obj = <span style="color: #2b91af;">JsonConvert</span>.DeserializeObject<<span style="color: #2b91af;">SerializationEventTestObject</span>>(json);</pre>
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<pre style="margin: 0px;"> </pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member1);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// 11</span></pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member2);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// This value went into the data file during serialization.</span></pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member3);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// This value was set during deserialization</span></pre>
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<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(obj.Member4);</pre>
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<pre style="margin: 0px;"><span style="color: green;">// This value was set after deserialization.</span></pre>
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