iOS6後的內存警告處理

【iOS6後的內存警告處理】

　　The memory used by a view to draw itself onscreen is potentially quite large. However, the system automatically releases these expensive resources when the view is not attached to a window. The remaining memory used by most views is small enough that it is not worth it for the system to automatically purge and recreate the view hierarchy.

　　iOS6後UIKit框架會自動將view中的圖片資源給釋放掉，而不會將view對象自己給釋放掉。由於和位圖內存相比，view對象自己所佔內存小到能夠忽略。因此iOS6起後，didReceiveMemoryWarning默認會作的事情是把把位圖資源釋放掉，簡而言之就是程序員不用再考慮了，UIKit會自動作。而view對象都會被保留。

　　若是程序員須要本身釋放資源，能夠這像下面這樣寫。

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Add code to clean up any of your own resources that are no longer necessary.
    if (self.isViewLoaded && [self.view window] == nil)
    {
        // Add code to preserve data stored in the views that might be
        // needed later.
 
        // Add code to clean up other strong references to the view in
        // the view hierarchy.
        self.view = nil;
    }

　　iOS5默認會釋放位圖資源與卸載view對象，iOS6默認只釋放位圖資源。而爲了統一處理，能夠用上述代碼，iOS6後自主卸載view對象。另外viewWillUnload與viewDidUnload這2個方法就沒有意義了，把想關代碼都移到上述代碼中便可。

參考：一、https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/ViewLoadingandUnloading/ViewLoadingandUnloading.html

二、http://justsee.iteye.com/blog/1820588