BroadcastReceiver 必须提供公共默认构造函数 - Xamarin.Android

Question

好的，我正在运行一个广播接收器：

public class SyncServiceBroadcastReceiver : BroadcastReceiver
{
    public static string syncStarted = "SyncRuns";

    private readonly PendingOrdersActivity pendingOrdersActivity;

    public SyncServiceBroadcastReceiver(PendingOrdersActivity pendingOrdersActivity)
    {
        this.pendingOrdersActivity = pendingOrdersActivity;
    }

    public override void OnReceive(Context context, Intent intent)
    {
        this.pendingOrdersActivity.RefreshPendingOrdersOnSync();

        Toast.MakeText(context, "Datele se actualizează...", ToastLength.Short).Show();
    }
}

每次命中时，我都希望它从活动中运行一个方法（方法 RefreshPendingOrdersOnSync）。这就是为什么我创建了一个接受活动的构造函数。

在我注册 BroadcastReceiver 的活动中，在 OnResume 方法中，通过传入“this”：

 var filter = new IntentFilter(SyncServiceBroadcastReceiver.syncStarted);
 filter.AddCategory(Intent.CategoryDefault);
 this.syncServiceBroadcastReceiver = new SyncServiceBroadcastReceiver(this);
 this.RegisterReceiver(this.syncServiceBroadcastReceiver, filter);

不过，在 Receiver 部分，它给出了标题中的错误.... 如果我添加一个空的构造函数，我怀疑它会通过那里并且 OnReceive 中的这一行会中断，因为 this.pendingOrdersActivity 是 null

this.pendingOrdersActivity.RefreshPendingOrdersOnSync();

我很困惑为什么

Answer 1

BroadcastReceiver 必须提供一个公共的默认构造函数

需要默认的构造方法。因为在使用AndroidManifest.xml注册BroadcastReceiver时，Android使用反射来实例化接收器，需要一个默认的构造函数。

参考：https://stackoverflow.com/a/14266261/11083277

如果我添加一个空构造函数，我怀疑它会通过那里并且 OnReceive 中的这一行会中断

我测试了一个基本的演示来测试代码，添加了默认的构造函数方法，代码工作正常。参数化的构造函数将被执行。你在AndroidManifest.xml注册了接收者吗？如果是这样，请尝试在代码中完成这项工作。

[BroadcastReceiver]
public class CustomReceiver : BroadcastReceiver
{
    private readonly MainActivity activity;

    public CustomReceiver()
    {
    }

    public CustomReceiver(MainActivity activity)
    {
        this.activity = activity;
    }
    public override void OnReceive(Context context, Intent intent)
    {
        activity.method();
    }
}

活动类

public class MainActivity : AppCompatActivity
{
    CustomReceiver receiver;
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        Xamarin.Essentials.Platform.Init(this, savedInstanceState);
        SetContentView(Resource.Layout.activity_main);

        receiver = new CustomReceiver(this);
    }
    public void method()
    {
        ...
    }

    protected override void OnResume()
    {
        base.OnResume();
        RegisterReceiver(receiver, new IntentFilter("package_name"));
    }

    protected override void OnDestroy()
    {
        base.OnDestroy();
        UnregisterReceiver(receiver);
    }
}