是 - [UIView（MyOwnCategory）drawRect：]從來沒有呼籲3.1.3？

Question

我定義了我自己的drawRect方法，它在4.2.1（iOS）5.0（iOS）和4.3.2（Simulator）中被調用。但它從未呼籲3.1.3（iPhone 2g）。

這是什麼原因？

P.S.因爲我開始寫這個問題，我想我的3.1.3設備已經越獄了。也許這是這種奇怪行爲的根源。

UPD：要重現問題，我使用下面的代碼：

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

例外，從來沒有發生過3.1.3甚至當我打電話[super drawRect: rect]明確

Answer 1

我現在就想寫寫方法混寫了幾個星期，凱文巴拉德的評論終於讓我做到了（謝謝你的啓發，凱文）。

因此，這裏是使用method swizzling你的問題的解決方案也應在iOS 3.x的工作：

的UIView + Border.h：

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

的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