Masonry使用小結：
1、equalTo：用于跟對象約束；
2、mas_equalTo：用于具體的數值；
3、沒有offset()：默認約束距離是零；

[self.okButton mas_makeConstraints:^(MASConstraintMaker *make) {
    make.top.equalTo(self.view);//頂部
    make.width.mas_equalTo(300);
    make.height.mas_equalTo(160);
    make.trailing.equalTo(self.view);//右邊
}];

[ImageView mas_makeConstraints:^(MASConstraintMaker *make) {
    make.top.equalTo(self.view).offset(16);//偏移16
    make.size.mas_equalTo(CGSizeMake(64,64));
    make.centerX.equalTo(self.view);//垂直居中
}];

[self.cancelButton mas_makeConstraints:^(MASConstraintMaker *make) {
    make.top.equalTo(self.holderView);
    make.leading.equalTo(self.holderView);
    make.bottom.equalTo(self.pickerView.mas_top);//底部跟頂部
    make.width.mas_equalTo(kButtonWidth);
}];