Introduction to block in iOS (i) basics

<span id="Label3"></p>Introduction to block in iOS (i) basic one, Overview<p><p>Block is a c-level syntax and runtime feature. Block is similar to the C function, but the block is more flexible than the C function, which is reflected in the stack memory, heap memory reference, and we can even pass a block as a parameter to other functions or block.</p></p><p><p></p></p>second, Warm Up<p><p>Let's look at a relatively simple block example:</p></p> <ol class="dp-cpp"> <ol class="dp-cpp"> <li class="alt"><span class="datatypes">int multiplier = 7;</span></li> <li><span class="datatypes">int (^myblock) (<span class="datatypes">int) = ^ (<span class="datatypes">int Num) {</span> </span></span></li> <li class="alt"><span class="keyword">return num * multiplier;</span></li> <li>};</li> </ol> </ol><p><p>In this example, Myblock is a block variable that takes a parameter of type int and returns a value of type int. Does it look like a C function?</p></p><p><p>Come on, let's have a typedef.</p></p> <ol class="dp-cpp"> <ol class="dp-cpp"> <li class="alt"><span class="keyword">typedef <span class="keyword">void (^boolblock) (<span class="datatypes">BOOL); <span class="comment"> A block that accepts only one bool parameter and no return value</span> </span> </span></span></li> <li><span class="keyword">typedef <span class="datatypes">INT (^intblock) (<span class="keyword">void); <span class="comment"> A block with no parameters that returns an int</span> </span> </span></span></li> <li class="alt"><span class="keyword">typedef boolblock (^HUGEBLOCK) (intblock); <span class="comment">//see, This hugeblock parameter and return value are block</span></span></li> </ol> </ol><p><p></p></p>third, more detailed examples <blockquote> <blockquote> <p>Note: the typedef above are also valid ~</p> </blockquote> </blockquote><p><p><strong>Take the initiative to Call:</strong></p></p> <ol class="dp-cpp"> <ol class="dp-cpp"> <li class="alt">-(<span class="keyword">void) SomeMethod</span></li> <li>{</li> <li class="alt">Boolblock Ablock = ^ (<span class="datatypes">BOOL BValue) {</span></li> <li>NSLog (@<span class="string">"Bool block!");</span></li> <li class="alt">};</li> <li>Ablock ();</li> <li class="alt">}</li> </ol> </ol><p><p><strong>Returned as a parameter:</strong></p></p> <ol class="dp-cpp"> <ol class="dp-cpp"> <li class="alt"><span class="keyword">typedef <span class="keyword">void (^boolblock) (<span class="datatypes">BOOL);</span> </span></span></li> <li>-(boolblock) Foo ()</li> <li class="alt">{</li> <li>Boolblock Ablock = ^ (<span class="datatypes">BOOL BValue) {</span></li> <li class="alt">NSLog (@<span class="string">"Bool block!");</span></li> <li>};</li> <li class="alt"><span class="keyword">return [[ablock copy] autorelease]; <span class="comment">//must copy, Copy it to the heap, more detailed principles, will be explained in the following chapters</span> </span></li> <li>}</li> </ol> </ol><p><p><strong>A member of the Class:</strong></p></p> <ol class="dp-cpp"> <ol class="dp-cpp"> <li class="alt">@interface Obj1:nsobject</li> <li>@property (nonatomic, copy) Boolblock block; <span class="comment">//reason ditto, Students</span></li> <li class="alt">@end</li> <li></li> <li class="alt">OBJ1 *obj1 = ...</li> <li>Obj1.block = ^ (<span class="datatypes">BOOL BValue) {</span></li> <li class="alt">NSLog (@<span class="string">"Bool block!");</span></li> <li>};</li> </ol> </ol><p><p><strong>Parameters for other Functions:</strong></p></p> <ol class="dp-cpp"> <ol class="dp-cpp"> <li class="alt">-(<span class="keyword">void) foo (boolblock block)</span></li> <li>{</li> <li class="alt"><span class="keyword">if (block) {</span></li> <li>Block ();</li> <li class="alt">}</li> <li>}</li> </ol> </ol><p><p><strong>Even other block parameters:</strong></p></p> <ol class="dp-cpp"> <ol class="dp-cpp"> <li class="alt">Boolblock bblock = ^ (<span class="datatypes">BOOL bV) {<span class="keyword">if (bv) {<span class="comment">/*do some thing*/}};</span> </span> </span></li> <li>Hugeblock Hblock = ^ (boolblock Bb) {bb ();};</li> <li class="alt"></li> <li>Hbolck (bblock);</li> </ol> </ol><p><p><strong>ah, Global variables! ：</strong></p></p> <ol class="dp-cpp"> <ol class="dp-cpp"> <li class="alt"><span class="keyword">static <span class="datatypes">int (^maxintblock) (<span class="datatypes">int, <span class="datatypes">int) = ^ (<span class="datatypes">int a, <span class="datatypes">int B) {<span class="keyword">return a>b?a:b;};</span> </span> </span> </span> </span></span></span></li> <li><span class="datatypes">int main ()</span></li> <li class="alt">{</li> <li>printf (<span class="string">"%d\n", maxintblock (2,10)); </span></li> <li class="alt"><span class="keyword">return 0;</span></li> <li>}</li> </ol> </ol><p><p>well, you know how the block might be used.</p></p><p><p></p></p>four, Special markings, __block<p><p>If you want to modify the stack variables declared outside of block within a block, be sure to add __block tags to the variable:</p></p> <ol class="dp-cpp"> <ol class="dp-cpp"> <li class="alt"><span class="datatypes">int main ()</span></li> <li>{</li> <li class="alt">__block <span class="datatypes">int i = 1024x768;</span></li> <li>Boolblock bblock = ^ (<span class="datatypes">BOOL BV) {</span></li> <li class="alt"><span class="keyword">if (bV) {</span></li> <li>i++; <span class="comment">//if There is no __block tag, it cannot be compiled. </span></li> <li class="alt">}</li> <li>};</li> <li class="alt">}</li> </ol> </ol><p><p>Introduction to block in iOS (i) basics</p></p></span>