UIImageView和UIScrollView加載大量圖片

Question

在我的應用程序中，我使用UIImageView和UIScrollView來顯示大量圖像（每次大約20張圖像，每張圖像大約600px * 500px，大小約600kb）。

我使用此代碼來完成這個功能：

// Here is pictures Data; 
self.klpArry = self.pictureData; 

CGSize size = self.klpScrollView1.frame.size; 
for (int i=0; i < [klpArr count]; i++) { 
    UIImageView *iv = [[UIImageView alloc] initWithFrame:CGRectMake((size.width * i)+300, 20, 546, 546)]; 
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[klpArr objectAtIndex:i] ofType:@"jpg"]; 
    UIImage *imageData = [[UIImage alloc]initWithData:[NSData dataWithContentsOfFile:filePath]]; 
    [iv setImage:imageData]; 
    iv.backgroundColor = [UIColor grayColor]; 
    [self.klpScrollView1 addSubview:iv]; 
    imageData = nil; 
    iv = nil; 
    iv.image = nil; 
    filePath = nil; 
    [imageData release]; 
    [filePath release]; 
    [iv release]; 
} 
    // show the picture in scrollview; 
[self.klpScrollView1 setContentSize:CGSizeMake(size.width * numImage, size.height)]; 
self.klpScrollView1.pagingEnabled = YES; 
self.klpScrollView1.showsHorizontalScrollIndicator = NO; 
self.klpScrollView1.backgroundColor = [UIColor grayColor]; 

但每次我初始化此功能時，內存將增加約5MB。其實我發佈了UIImageView,UIimage和UIScrollView（vi.image=nil, [vi release]）但它不起作用，分配的內存沒有被釋放。順便說一句，我用我的朋友的代碼第一vi.image = nil然後vi = nil;但圖片不會顯示在滾動視圖上。

Answer 1

的主要問題，在我看來，是你設置你的局部變量nil，然後你繼續嘗試使用這些本地像release之類的方法中的變量，但因爲它們已被設置爲nil，這些方法現在什麼也不做，而具有+1 retainCount（或現在+2因爲您已將它們添加到視圖中）的對象永遠不會釋放。

因此，我建議如下：

//Here is pictures Data; 
self.klpArry = self.pictureData; 

CGSize size = self.klpScrollView1.frame.size; 
for (int i=0; i < [klpArr count]; i++) { 
    UIImageView *iv = [[UIImageView alloc] initWithFrame:CGRectMake((size.width * i)+300, 20, 546, 546)]; 
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[klpArr objectAtIndex:i] ofType:@"jpg"]; 
    UIImage *imageData = [[UIImage alloc]initWithData:[NSData dataWithContentsOfFile:filePath]]; 
    [iv setImage:imageData]; 
    iv.backgroundColor = [UIColor grayColor]; 
    [self.klpScrollView1 addSubview:iv]; 

    // Don't set these to nil, or else subsequent release statements do nothing! 
    // These statements are actually not necessary because they refer to local 
    // variables so you don't need to worry about dangling pointers. Make sure 
    // you're not confusing the purpose of setting a pointer to nil in ARC to 
    // what you're doing in your non-ARC code. 
    // 
    // imageData = nil; 
    // iv = nil; 

    // You don't want to set this to nil because if iv is not nil, your image 
    // will be removed from your imageview. So, not only is this not needed, 
    // but it's undesired. 
    // 
    // iv.image = nil; 

    // This statement is not necessary for the same reason you don't do it 
    // to imageData or iv, either. This is probably even worse, though, because 
    // filePath is not a variable that you initialized via alloc. You should 
    // only be releasing things you created with alloc (or new, copy, mutableCopy, 
    // for which you issued a retain statement). 
    // 
    // filePath = nil; 

    [imageData release]; 

    // filePath is a +0 retainCount already, so don't release. You only release 
    // those items for which you increased retainCount (e.g. via new, copy, 
    // mutableCopy, or alloc or anything you manually retained). 
    // 
    // [filePath release]; 

    [iv release]; 
} 

// show the picture in scrollview; 
[self.klpScrollView1 setContentSize:CGSizeMake(size.width * numImage, size.height)]; 
self.klpScrollView1.pagingEnabled = YES; 
self.klpScrollView1.showsHorizontalScrollIndicator = NO; 
self.klpScrollView1.backgroundColor = [UIColor grayColor]; 

因此，你的代碼將被簡化（和糾正），以可能只是：

//Here is pictures Data; 
self.klpArry = self.pictureData; 

CGSize size = self.klpScrollView1.frame.size; 
for (int i=0; i < [klpArr count]; i++) { 
    UIImageView *iv = [[UIImageView alloc] initWithFrame:CGRectMake((size.width * i)+300, 20, 546, 546)]; 
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[klpArr objectAtIndex:i] ofType:@"jpg"]; 
    UIImage *imageData = [[UIImage alloc] initWithData:[NSData dataWithContentsOfFile:filePath]]; 
    [iv setImage:imageData]; 
    iv.backgroundColor = [UIColor grayColor]; 
    [self.klpScrollView1 addSubview:iv]; 
    [imageData release]; 
    [iv release]; 
} 

// show the picture in scrollview; 
[self.klpScrollView1 setContentSize:CGSizeMake(size.width * numImage, size.height)]; 
self.klpScrollView1.pagingEnabled = YES; 
self.klpScrollView1.showsHorizontalScrollIndicator = NO; 
self.klpScrollView1.backgroundColor = [UIColor grayColor]; 

或者你可以進一步簡化代碼通過使用autorelease：

//Here is pictures Data; 
self.klpArry = self.pictureData; 

CGSize size = self.klpScrollView1.frame.size; 
for (int i=0; i < [klpArr count]; i++) { 
    UIImageView *iv = [[[UIImageView alloc] initWithFrame:CGRectMake((size.width * i)+300, 20, 546, 546)] autorelease]; 
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[klpArr objectAtIndex:i] ofType:@"jpg"]; 
    UIImage *imageData = [[[UIImage alloc] initWithData:[NSData dataWithContentsOfFile:filePath]] autorelease]; 
    [iv setImage:imageData]; 
    iv.backgroundColor = [UIColor grayColor]; 
    [self.klpScrollView1 addSubview:iv]; 
} 

// show the picture in scrollview; 
[self.klpScrollView1 setContentSize:CGSizeMake(size.width * numImage, size.height)]; 
self.klpScrollView1.pagingEnabled = YES; 
self.klpScrollView1.showsHorizontalScrollIndicator = NO; 
self.klpScrollView1.backgroundColor = [UIColor grayColor]; 

順便說一句，語句（autorelease）：

UIImage *imageData = [[[UIImage alloc] initWithData:[NSData dataWithContentsOfFile:filePath]] autorelease]; 

也許可以簡化爲：

UIImage *imageData = [UIImage imageWithContentsOfFile:filePath]; 

這給你一個UIImage，用+0 retainCount（即你不需要release它）從你的文件。

所以，一些結論性意見：

1. 你真的應該大概檢討和研究的Advanced Memory Management Programming Guide。如果你對存儲器管理不熟悉，那麼讀起來很密集，但掌握這些概念（特別是在非ARC代碼中）是至關重要的。

2. 如果你還沒有，我會鼓勵你通過靜態分析（「產品」 - 「分析」或轉變 + 命令 + 乙）來運行代碼。如果很多（如果不是大多數）這些問題不會被分析儀識別出來，我會很驚訝。通過分析器運行代碼時，您應該沒有任何警告。

3. 如果你想把它提升到一個新的水平，你可能想對你的內存管理更加保守。治理原則將是一個系統設計，只加載在任何給定的時間在用戶界面上需要的圖像，這不僅涉及到calvinBhai對圖像延遲加載的出色建議（即，不會將圖像加載到內存中，直到您的UI 真的需要它們），但也是一個積極主動釋放圖像，一旦他們已經滾動屏幕。也許你不需要在你的應用中擔心它，因爲你一次只能處理20張圖片，但是如果你的任何投資組合/畫廊擴展到100或1000張圖片，那麼保留所有這些圖片的想法記憶在任何時候都是一個壞主意。這是一個更先進的概念，所以也許你應該首先關注現有代碼的基本內存管理問題，但是從更長遠的角度來看，您可能需要考慮延遲加載和主動釋放圖像。

Answer 2

如果內存是你的關心，

嘗試延遲加載圖像=負載可見圖像，下一個和以前的形象。您不必將所有圖像添加到您的klpscrollview。

一旦你找出延遲加載到你的滾動視圖的圖像，那麼你可以考慮修復不顯示在你的滾動視圖上的圖像。

更容易

將搜索「延遲加載的UIImage的UIScrollView」