使用 protobuf 类型

由于 Google Ads API 使用 proto3 作为其默认载荷格式，因此在使用 .NET 客户端库时，请务必了解一些协议缓冲区惯例和类型。

可选字段

Google Ads API 中的许多字段都标记为 optional。这样，您就可以区分字段具有空值的情况与服务器未返回字段值的情况。这些字段的行为类似于常规属性，但它们还提供了其他方法来清除字段以及检查字段是否已设置。

例如，Campaign 对象的 Name 字段被标记为 optional，因此您可以使用以下方法来处理此字段：

// Get the name.
string name = campaign.Name;

// Set the name.
campaign.Name = name;

// Check if the campaign object has the name field set.
bool hasName = campaign.HasName();

// Clear the name field. Use this method to exclude the Name field from
// being sent to the server in a subsequent API call.
campaign.ClearName();

// Set the campaign name to an empty string value. This value will be
// sent to the server if you use this object in a subsequent API call.
campaign.Name = "";

// This throws a runtime ArgumentNullException. Use ClearName() instead.
campaign.Name = null;

重复字段

在 Google Ads API 中，字段数组表示为只读 RepeatedField。

例如，广告系列的 url_custom_parameters 字段是一个重复字段，因此在 .NET 客户端库中表示为只读 RepeatedField<CustomParameter>。RepeatedField<T> 会实现 IList<T> 接口。

您可以通过以下两种方式填充 RepeatedField 属性：

AddRange 方法

Campaign campaign = new Campaign()
{
    ResourceName = ResourceNames.Campaign(customerId, campaignId),
    Status = CampaignStatus.Paused,
};

// Add values to UrlCustomParameters using the AddRange method.
campaign.UrlCustomParameters.AddRange(new CustomParameter[]
{
    new CustomParameter { Key = "season", Value = "christmas" },
    new CustomParameter { Key = "promocode", Value = "NY123" }
});

集合初始化程序语法

// Option 1: Initialize the field directly.
Campaign campaign = new Campaign()
{
    ResourceName = ResourceNames.Campaign(customerId, campaignId),
    Status = CampaignStatus.Paused,
    // Directly initialize the field.
    UrlCustomParameters =
    {
        new CustomParameter { Key = "season", Value = "christmas" },
        new CustomParameter { Key = "promocode", Value = "NY123" }
    }
};

// Option 2: Initialize using an intermediate variable.
CustomParameter[] parameters = new CustomParameter[]
{
    new CustomParameter { Key = "season", Value = "christmas" },
    new CustomParameter { Key = "promocode", Value = "NY123" }
};

Campaign campaign1 = new Campaign()
{
    ResourceName = ResourceNames.Campaign(customerId, campaignId),
    Status = CampaignStatus.Paused,
    // Initialize from an existing array.
    UrlCustomParameters = { parameters }
};

Oneof 字段

Google Ads API 中的某些字段会被标记为 oneof 字段，这意味着该字段可以包含不同类型的值，但在给定时间只能包含一个值。oneof 字段类似于 C 编程语言中的联合类型。

.NET 库通过为 oneof 字段中可包含的每种类型的值提供一个属性来实现 oneof 字段，所有属性都会更新共享底层存储字段。

例如，广告系列的 campaign_bidding_strategy 会标记为 oneof 字段。该类的实现方式如下（为简洁起见，代码已简化）：

public sealed partial class Campaign : pb::IMessage<Campaign>
{
    object campaignBiddingStrategy_ = null;
    CampaignBiddingStrategyOneofCase campaignBiddingStrategyCase_;

    public ManualCpc ManualCpc
    {
        get
        {
            return campaignBiddingStrategyCase_ ==
                CampaignBiddingStrategyOneofCase.ManualCpc
                ? (ManualCpc)campaignBiddingStrategy_ : null;
        }
        set
        {
            campaignBiddingStrategy_ = value;
            campaignBiddingStrategyCase_ =
                CampaignBiddingStrategyOneofCase.ManualCpc;
        }
    }

    public ManualCpm ManualCpm
    {
        get
        {
            return campaignBiddingStrategyCase_ ==
                CampaignBiddingStrategyOneofCase.ManualCpm
                ? (ManualCpm)campaignBiddingStrategy_ : null;
        }
        set
        {
            campaignBiddingStrategy_ = value;
            campaignBiddingStrategyCase_ =
                CampaignBiddingStrategyOneofCase.ManualCpm;
        }
    }

    public CampaignBiddingStrategyOneofCase CampaignBiddingStrategyCase
    {
        get { return campaignBiddingStrategyCase_; }
    }
}

由于 oneof 属性共享存储空间，因此一项分配可能会覆盖之前的分配，从而导致细微的 bug。例如：

Campaign campaign = new Campaign()
{
    ManualCpc = new ManualCpc(),
    ManualCpm = new ManualCpm()
};

在这种情况下，campaign.ManualCpc 为 null，因为初始化 campaign.ManualCpm 属性会覆盖 campaign.ManualCpc 的上一次初始化。

转换为其他格式

转换为 JSON 格式

您可以使用 Google.Protobuf.JsonFormatter 将 protobuf 对象转换为 JSON 格式，也可以反向转换。在构建需要与其他系统（需要 JSON 或 XML 等基于文本的格式）对接的系统时，这非常有用。

using Google.Protobuf;

GoogleAdsRow row = new GoogleAdsRow()
{
    Campaign = new Campaign()
    {
        Id = 123,
        Name = "Campaign 1",
        ResourceName = ResourceNames.Campaign(1234567890, 123)
    }
};

// Serialize to JSON and back.
string json = JsonFormatter.Default.Format(row);
row = GoogleAdsRow.Parser.ParseJson(json);

转换为字节

您可以使用 Google.Protobuf 将对象序列化为字节，然后再反序列化。二进制序列化比 JSON 格式更节省内存和存储空间。

using Google.Protobuf;

GoogleAdsRow row = new GoogleAdsRow()
{
    Campaign = new Campaign()
    {
        Id = 123,
        Name = "Campaign 1",
        ResourceName = ResourceNames.Campaign(1234567890, 123)
    }
};

// Serialize to bytes and back.
byte[] bytes = row.ToByteArray();
row = GoogleAdsRow.Parser.ParseFrom(bytes);