Artigo
11/18/2011

ILGenerator.Emit Method (OpCode, Label)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Puts the specified instruction onto the Microsoft intermediate language (MSIL) stream and leaves space to include a label when fixes are done.

Namespace: System.Reflection.Emit
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Overridable Sub Emit ( _
    opcode As OpCode, _
    label As Label _
)

public virtual void Emit(
    OpCode opcode,
    Label label
)

Parameters

opcode
Type: System.Reflection.Emit.OpCode
The MSIL instruction to be emitted onto the stream.

label
Type: System.Reflection.Emit.Label
The label to branch to.

Remarks

The instruction values are defined in the OpCodes enumeration.

Labels are created by using the DefineLabel method, and their location within the stream is fixed by using the MarkLabel method. If a single-byte instruction is used, the label can represent a jump of at most 127 bytes along the stream. opcode must represent a branch instruction. Because branches are relative instructions, label will be replaced with the correct offset to branch during the fixup process.

Examples

The following example demonstrates the use of the Emit(OpCode, Label) method overload to emit a conditional branch to a Label.

This code is part of a larger example provided for the BeginExceptionBlock method.

adderIL.BeginFinallyBlock()

' The finally block block displays a message on the TextBlock, if the 
' OutputBlock field has been set. Just as in the catch block, the following
' code tests whether the TextBlock is present, and skips the output if it is
' not present.
adderIL.Emit(OpCodes.Ldsfld, demoOutput)
adderIL.Emit(OpCodes.Ldnull)
adderIL.Emit(OpCodes.Ceq)
adderIL.Emit(OpCodes.Brtrue_S, skipOutputInFinally)

' Append a constant string to the Text property of the TextBlock.
adderIL.Emit(OpCodes.Ldsfld, demoOutput)
adderIL.Emit(OpCodes.Ldsfld, demoOutput)
adderIL.Emit(OpCodes.Callvirt, getter)
adderIL.Emit(OpCodes.Ldstr, "Executing the finally block." & vbLf)
adderIL.Emit(OpCodes.Call, concat2)
adderIL.Emit(OpCodes.Callvirt, setter)

adderIL.MarkLabel(skipOutputInFinally)
' This is the end of the try/catch/finally block.
adderIL.EndExceptionBlock()

adderIL.BeginFinallyBlock();

// The finally block block displays a message on the TextBlock, if the 
// OutputBlock field has been set. Just as in the catch block, the following
// code tests whether the TextBlock is present, and skips the output if it is
// not present.
adderIL.Emit(OpCodes.Ldsfld, demoOutput);
adderIL.Emit(OpCodes.Ldnull);
adderIL.Emit(OpCodes.Ceq);
adderIL.Emit(OpCodes.Brtrue_S, skipOutputInFinally);

// Append a constant string to the Text property of the TextBlock.
adderIL.Emit(OpCodes.Ldsfld, demoOutput);
adderIL.Emit(OpCodes.Ldsfld, demoOutput);
adderIL.Emit(OpCodes.Callvirt, getter);
adderIL.Emit(OpCodes.Ldstr, "Executing the finally block.\n");
adderIL.Emit(OpCodes.Call, concat2);
adderIL.Emit(OpCodes.Callvirt, setter);

adderIL.MarkLabel(skipOutputInFinally);
// This is the end of the try/catch/finally block.
adderIL.EndExceptionBlock();

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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