自定義三個(gè)model類分別為OneModel、TwoModel、AllModel
OneModel.h為

@property(nonatomic ,copy)NSString *oneName;

TwoModel.h為

@property(nonatomic ,copy)NSString *twoName;

AllModel.h為

@property(nonatomic ,strong)OneModel *oneModel;
@property(nonatomic ,strong)TwoModel *twoModel;

接下來(lái)要對(duì)AllModel的實(shí)例化對(duì)象賦值

AllModel *model = [AllModel new];
if(model.oneModel.oneName == nil){
        model.oneModel.oneName = @"123";
}else{
        [model.oneModel setValue:@"abc" forKey:@"oneName"];
}

model.twoModel.twoName = @"789";
[model.twoModel setValue:@"xyz" forKey:@"twoName"];

以上對(duì)model賦值全為nil。
原因，沒(méi)有給對(duì)象初始化。如果要進(jìn)行賦值：

AllModel *model = [AllModel new];
OneModel *model1 = [OneModel new];
TwoModel *model2 = [TwoModel new];

model1.oneName = @"123"; 
model2.twoName = @"789";

model.oneModel = model1;
model.twoModel = model2;