检查是否支持UIGraphicsBeginImageContextWithOptions [英] Checking if UIGraphicsBeginImageContextWithOptions is supported

问题描述

我正在使用iOS应用程式。它目前只适用于iOS 4，因为我在几个场合使用以下方法：UIGraphicsBeginImageContextWithOptions。这个方法只适用于iOS 4，因此我的应用程序当前崩溃/不工作在iPhone OS 3.除了这种方法，没有理由应用程序不应该在iPhone OS 3上工作。如何进行检查看到wether还是不是这种方法可用？我尝试下面没有成功：

I'm working on an iOS app. It currently only works on iOS 4 since I use the following method on several occasions: "UIGraphicsBeginImageContextWithOptions". This method is only available in iOS 4 and therefor my app currently crashes/doesn't work on iPhone OS 3. Aside from this method there is no reason why the app should not work on iPhone OS 3. How do I make a check to see wether or not this method is available ? I've tried the following without succes:

if([self respondsToSelector:@selector(UIGraphicsBeginImageContextWithOptions)]) {
    UIGraphicsBeginImageContextWithOptions(targetSize, NO, 0.0); // this will crop
}
else 
{
    UIGraphicsBeginImageContext(targetSize);

}

我只尝试过这样的变体：

I've only tried variations like this:

if([self respondsToSelector:@selector(UIGraphicsBeginImageContextWithOptions:size:opaque:scale:)])

和

if([self respondsToSelector:@selector(UIGraphicsBeginImageContextWithOptions:)])

任何帮助将不胜感激。

推荐答案

UIGraphicsBeginImageContextWithOptions是一个C函数，因此您不能使用Objective- c $ c> -respondsToSelector：来测试它的存在。

UIGraphicsBeginImageContextWithOptions is a C function, so you can't use Objective-C methods like -respondsToSelector: to test its existence.

然而，你可以

You could, however, weak link the UIKit framework, and then check if UIGraphicsBeginImageContextWithOptions is NULL:

if (UIGraphicsBeginImageContextWithOptions != NULL) {
   UIGraphicsBeginImageContextWithOptions(...);
} else {
   UIGraphicsBeginImageContext(...);
}

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