代码写Button遇到问题

夜晚本来像用代码写一个Button按钮，但是出现问题：开始是这样创建的

- (void)viewDidLoad
{    
    [super viewDidLoad];

//初始化Button的位置大小
    UIButton *writeButton = [[UIButton alloc] initWithFrame:CGRectMake(100.0f, 100.0f, 50.0f, 30.0f)];
    //设置BUtton的形状，此处为圆角按钮
    writeButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    //设置Button名字，和他的状态，此处是一般的状态
    [writeButton setTitle:@"代码按钮" forState:UIControlStateNormal];
    //Button背景色
    writeButton.backgroundColor = [UIColor redColor];
    //Button的触摸事件
    [writeButton addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
    //把Button添加到视图之上
    [self.view addSubview:writeButton];
}

按照这个看似没问题，但是在模拟器上运行的时候，Button并没有出现，用模拟器分析显示Value stored to 'writeButton' during its initialization is never read(值存储到“writeButton”在其初始化是从来没有读过)

- (void)viewDidLoad
{    
    [super viewDidLoad];
    UIButton *writeButton = [[UIButton alloc] init];
    
    CGRect frame = CGRectMake(100.0f, 100.0f, 50.0f, 30.0f);
    
    writeButton.frame= frame;
    
    writeButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    
    [writeButton setTitle:@"代码按钮" forState:UIControlStateNormal];
    
    writeButton.backgroundColor = [UIColor redColor];
    
    [writeButton addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
    
    [self.view addSubview:writeButton];
}

这样写在模拟器上也没有显示Button

- (void)viewDidLoad
{    
    [super viewDidLoad];
    UIButton *writeButton = [[UIButton alloc] init];
    
    CGRect frame = CGRectMake(100.0f, 100.0f, 100.0f, 30.0f);
    
        
    writeButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    
    writeButton.frame= frame;

    
    [writeButton setTitle:@"代码按钮" forState:UIControlStateNormal];
    
    writeButton.backgroundColor = [UIColor redColor];
    
    [writeButton addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
    
    [self.view addSubview:writeButton];
}

当这样写的时候才出现Button在模拟器视图上，于是啄么着是Button初始化frame时候，没有确定Button类型（此处是UIButtonTypeRoundedRect），
但是由product----》Analyze 又出现Value stored to 'writeButton' during its initialization is never read



再次修改

- (void)viewDidLoad
{    
    [super viewDidLoad];
    
    
    CGRect frame = CGRectMake(100.0f, 100.0f, 100.0f, 30.0f);
    UIButton *writeButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        
//    writeButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    
    writeButton.frame= frame;

    
    [writeButton setTitle:@"代码按钮" forState:UIControlStateNormal];
    
    writeButton.backgroundColor = [UIColor redColor];
    
    [writeButton addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
    
    [self.view addSubview:writeButton];
}

难道是因为不需要初始化吗？ 这个问题暂时不能理解