1. block捕捉變數:

結論：只有呼叫_Block_copy 才能持有截獲的附有 __strong 修飾符的物件型別的自動變數值。

block 中使用物件型別的自動變數時，除以下情形，推薦使用copy方法：

• “When the Block is returned from a function
• When the Block is assigned to a member variable of id or the Block type class, with a __strong qualifier
• When the Block is passed to a method, including “usingBlock” in the Cocoa Framework, or a Grand Central Dispatch API”

blk_t blk;
{
    id array = [[NSMutableArray alloc] init];
    blk = [^(id obj) {
        [array addObject:obj];
        NSLog(@"array count = %ld", [array count]);
    } copy];
}//由於copy，所以block持有array，所以超出作用域依然存在
blk([[NSObject alloc] init]); //array count = 1
blk([[NSObject alloc] init]); //array count = 2
blk([[NSObject alloc] init]); //array count = 3
 

blk_t blk 不執行copy情況：

{
    id array = [[NSMutableArray alloc] init];
    blk = ^(id obj) {
        [array addObject:obj];
        NSLog(@"array count = %ld", [array count]);
    };
}
//超出id 作用域，_ _strong 修飾的物件被釋放。
blk([[NSObject alloc] init]); //outPut:程式強行結束。
blk([[NSObject alloc] init]);
blk([[NSObject alloc] init]);”