ios8調用相機報警告: Snapshotting a view that has not been rendered results in an empty snapshot. Ensure yo

轉載自：  http://bbs.yusian.com/thread-10352-1-1.html

我這也報了這個警告,但按他的方法並沒有起作用,把寫到這個地方看是否其他人用的到

錯誤代碼：Snapshotting a view that has not been rendered results in an empty snapshot. Ensure your view has been rendered at least once before snapshotting or snapshot after screen updates.

問題分析：iOS8在調用系統相機拍照時，會有一兩秒的停頓，然後再彈出UIImagePickConroller，IOS7是沒有這個問題的，在百度找了無數遍都沒能解決這個問題，有說要將imagePickController設置爲全局變量，有說要延時0.5秒再presentViewController的，各顯神通，但很遺憾的都沒能解決這個問題，今天特意單獨寫個Demo來研究此問題，終於取得了突破性的進展！

其實根本原因不在於系統拍照控制器上面，而是執行presentViewController這個動作本身！我們可以查看下UIViewController這個類，他有一個屬性

[Objective-C] 純文本查看 複製代碼

@property(nonatomic,assign) UIModalPresentationStyle modalPresentationStyle NS_AVAILABLE_IOS(3_2);

這是一個枚舉值，在iOS7的SDK中，定義如下：

[Objective-C] 純文本查看 複製代碼

typedefNS_ENUM(NSInteger, UIModalPresentationStyle) {

    UIModalPresentationFullScreen = 0,

#if __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_3_2

    UIModalPresentationPageSheet,

    UIModalPresentationFormSheet,

    UIModalPresentationCurrentContext,

#endif

#if __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_7_0

    UIModalPresentationCustom,

    UIModalPresentationNone = -1,       

#endif       

};

在iOS8的SDK中定義如下：

[Objective-C] 純文本查看 複製代碼

typedefNS_ENUM(NSInteger, UIModalPresentationStyle) {

        UIModalPresentationFullScreen = 0,

        UIModalPresentationPageSheetNS_ENUM_AVAILABLE_IOS(3_2),

        UIModalPresentationFormSheetNS_ENUM_AVAILABLE_IOS(3_2),

        UIModalPresentationCurrentContextNS_ENUM_AVAILABLE_IOS(3_2),

        UIModalPresentationCustomNS_ENUM_AVAILABLE_IOS(7_0),

        UIModalPresentationOverFullScreenNS_ENUM_AVAILABLE_IOS(8_0),

        UIModalPresentationOverCurrentContextNS_ENUM_AVAILABLE_IOS(8_0),

        UIModalPresentationPopoverNS_ENUM_AVAILABLE_IOS(8_0),

        UIModalPresentationNoneNS_ENUM_AVAILABLE_IOS(7_0) = -1,        

};

解決問題的關鍵部分來了，IOS8多了一個樣式UIModalPresentationOverCurrentContext，IOS8中presentViewController時請將控制器的modalPresentationStyle設置爲UIModalPresentationOverCurrentContext，問題解決！！

[Objective-C] 純文本查看 複製代碼

if([[[UIDevice currentDevice] systemVersion] floatValue]>=8.0) {

    self.modalPresentationStyle=UIModalPresentationOverCurrentContext;

}