Is-从未在3.1.3上调用过[UIWiew(MyOwnCategory)drawRect:]

Question

我定义了自己的drawRect方法，它在4.2.1（iOS）5.0（iOS）和4.3.2（Simulator）上被成功调用。但它从未调用3.1.3（iPhone 2g）。

这可能是什么原因？

附言：自从我开始写这个问题以来，我认为我的3.1.3设备已经越狱了。也许这是这种奇怪行为的根本原因。

Upd：为了重现问题，我使用下一个代码：

@implementation UIView (MyOwnCategory)
- (void)drawRect:(CGRect)rect
{
    const char * function = __FUNCTION__;
    [NSException raise: @"hi!" format: @"%s", function];
}
@end

3.1.3上从未发生异常，即使我显式调用[super drawRect: rect]时也是如此

我想写几周关于Method Swizzling的文章，@Kevin Ballard的评论终于让我做到了（谢谢你的启发，Kevin）。

因此，这里有一个使用swizzling方法解决您的问题的解决方案，该方法也应该适用于iOS3.x：

UIView+Border.h：

#import <Foundation/Foundation.h>
@interface UIView(Border)
@end

UIView+Border.m:

#import "UIView+Border.h"
#import <QuartzCore/QuartzCore.h>
#import <objc/runtime.h>
@implementation UIView(Border)
- (id)swizzled_initWithFrame:(CGRect)frame
{
    // This is the confusing part (article explains this line).
    id result = [self swizzled_initWithFrame:frame];
    // Safe guard: do we have an UIView (or something that has a layer)?
    if ([result respondsToSelector:@selector(layer)]) {
        // Get layer for this view.
        CALayer *layer = [result layer];
        // Set border on layer.
        layer.borderWidth = 2;
        layer.borderColor = [[UIColor redColor] CGColor];
    }
    // Return the modified view.
    return result;
}
- (id)swizzled_initWithCoder:(NSCoder *)aDecoder
{
    // This is the confusing part (article explains this line).
    id result = [self swizzled_initWithCoder:aDecoder];
    // Safe guard: do we have an UIView (or something that has a layer)?
    if ([result respondsToSelector:@selector(layer)]) {
        // Get layer for this view.
        CALayer *layer = [result layer];
        // Set border on layer.
        layer.borderWidth = 2;
        layer.borderColor = [[UIColor blueColor] CGColor];
    }
    // Return the modified view.
    return result;
}
+ (void)load
{
    // The "+ load" method is called once, very early in the application life-cycle.
    // It's called even before the "main" function is called. Beware: there's no
    // autorelease pool at this point, so avoid Objective-C calls.
    Method original, swizzle;
    // Get the "- (id)initWithFrame:" method.
    original = class_getInstanceMethod(self, @selector(initWithFrame:));
    // Get the "- (id)swizzled_initWithFrame:" method.
    swizzle = class_getInstanceMethod(self, @selector(swizzled_initWithFrame:));
    // Swap their implementations.
    method_exchangeImplementations(original, swizzle);
    // Get the "- (id)initWithCoder:" method.
    original = class_getInstanceMethod(self, @selector(initWithCoder:));
    // Get the "- (id)swizzled_initWithCoder:" method.
    swizzle = class_getInstanceMethod(self, @selector(swizzled_initWithCoder:));
    // Swap their implementations.
    method_exchangeImplementations(original, swizzle);
}
@end