調(diào)試的過(guò)程中還是得注意這個(gè)，不然字典莫名其妙的少了點(diǎn)keys，定位很麻煩。

給NSDictionary設(shè)置value時(shí)--value為nil時(shí)程序會(huì)不會(huì)crash？

答：分情況

• 使用字面量，會(huì)crash

• 使用setObject:ForKey:會(huì)crash，

• 使用dictionaryWithObjectsAndKeys：不會(huì)crash，

• 使用setValue：ForKey：不會(huì)crash。

• 直接賦值dict[@"key"]=nil：不會(huì)crash。

詳細(xì)情況可以看下面注釋

    NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                          @"99", @"key1",
                          @"02", @"key2",
                          [self value],@"key3",
                          @"end",@"end", nil]; 
// 編譯運(yùn)行都可以通過(guò),但是當(dāng)[self value]為空時(shí),后面所有的key和value都無(wú)法添加上了,但是沒(méi)有添加上key&value


    NSDictionary *dict2 = @{
        @"key1": @"99",
        @"key2": @"02",
        @"key3":[self value],
        @"end":@"end"}; 
//*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[2]'
    
    
    [dict setValue:[self value] forKey:@"value"]; 
// 編譯運(yùn)行都可以通過(guò),但是沒(méi)有添加上key&value,不影響后面的setValue執(zhí)行

    [dict setValue:@"~~~" forKey:@"value2"];
    [dict setValue:@"[self value]" forKey:@"value3"];
    [dict setValue:@"[self " forKey:@"value4"];
    dict[@"value"] = [self value]; 
    // 直接賦值也沒(méi)有問(wèn)題

    [dict setObject:[self value] forKey:@"value"]; 
// *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSDictionaryM setObject:forKey:]: object cannot be nil (key: value)'
    NSLog(@"%@", dict);