iOS Guides | Samples

MonoTouch.UIKit.UIImage Constructor

Constructor to call on derived classes to skip initialization and merely allocate the object.

Syntax

[System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Advanced)]
public UIImage (NSObjectFlag t)

Parameters

t
Unused sentinel value, pass NSObjectFlag.Empty.

Remarks

This constructor should be called by derived classes when they completely construct the object in managed code and merely want the runtime to allocate and initialize the NSObject. This is required to implement the two-step initialization process that Objective-C uses, the first step is to perform the object allocation, the second step is to initialize the object. When you invoke the constructor that takes the NSObjectFlag.Empty you taking advantage of a direct path that goes all the way up to NSObject to merely allocate the object's memory and bind the Objective-C and C# objects together. The actual initialization of the object is up to you.

This constructor is typically used by the binding generator to allocate the object, but prevent the actual initialization to take place. Once the allocation has taken place, the constructor has to initialize the object. With constructors generated by the binding generator this means that it manually invokes one of the "init" methods to initialize the object.

It is your responsibility to completely initialize the object if you chain up using the NSObjectFlag.Empty path.

In general, if your constructors invokes the NSObjectFlag.Empty base implementation, then it should be calling an Objective-C init method. If this is not the case, you should instead chain to the proper constructor in your class.

The argument value is ignored and merely ensures that the only code that is executed is the construction phase is the basic NSObject allocation and runtime type registration. Typically the chaining would look like this:

C# Example

//
// The NSObjectFlag merely allocates the object and registers the
// C# class with the Objective-C runtime if necessary, but no actual
// initXxx method is invoked, that is done later in the constructor
//
// This is taken from MonoTouch's source code:
//
[Export ("initWithFrame:")]
public UIView (System.Drawing.RectangleF frame) : base (NSObjectFlag.Empty)
{
// Invoke the init method now.
	var initWithFrame = new Selector ("initWithFrame:").Handle;
	if (IsDirectBinding)
		Handle = MonoTouch.ObjCRuntime.Messaging.IntPtr_objc_msgSend_RectangleF (this.Handle, initWithFrame, frame);
	else
		Handle = MonoTouch.ObjCRuntime.Messaging.IntPtr_objc_msgSendSuper_RectangleF (this.SuperHandle, initWithFrame, frame);
}

Requirements

Namespace: MonoTouch.UIKit
Assembly: monotouch (in monotouch.dll)
Assembly Versions: 0.0.0.0