TEchnical Cites

  • 06:17:25 am on February 16, 2009 | 0

    iPhone OS does not write volatile pages to disk when memory gets full

    iPhone OS virtual memory model does not include disk swap space,

    you must be careful to allocate no more memory than is available on the device

    The file system for iPhone OS – based devices is case sensitive

    Each thread of a process has its own run loop

    If the application is launched through a URL, the system looks for a launch image named Default-scheme.png, where scheme is the scheme of the URL. If that file is not present, it chooses Default.png instead.

    The view is actually a lightweight wrapper for an underlying layer. The view provides event handling and the layer provides the drawing.

    When you set the transform property, use the center and bounds properties to get the location and size of the view, not the frame property.

    It’s true that superviews in the view hierarchy are drawn before subviews and subviews are drawn from back to front.

    In many cases simply configuring the autoresizing mask for a view provides the appropriate behavior for an
    application. Otherwise, it is the application’s responsibility to reposition and resize the subviews by
    overriding the layoutSubviews method.

    by default the current context buffer in the drawRect: method is automatically filled with transparent black before the drawRect: is invoked. You can change this behavior by setting the clearsContextBeforeDrawing property to NO and thereby, improve drawing performance.

    When creating custom contexts, the origin being in the lower-left corner of the drawing surface and the axes point up and to the right. Quartz images assume a coordinate system with a lower-left corner origin and positive coordinate axes extending up and to the right from that point

    Drawing Models

    Vector based
    Raster based

    Your drawing code should always use RGB colors.

    iPhone OS includes an optimized drawing path for PNG images that is typically more efficient than other formats

    If you need to present an image at variable sizes, include multiple versions of the image at different sizes and scale down from an image that is relatively close to the target size.

    To implement transparency , use alpha blending instead of alpha testing. Alpha testing is considerably more expensive than alpha blending.

    when you answer a phone call, the iPhone quits the currently active application and then re-starts it after you hang up.


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