屏幕（un）锁定事件中的Xamarin C＃活动

Question

只是想知道在Xamarin中是否有活动类的事件，如OnStart，OnResume，OnPause等，当用户在应用程序打开时锁定或解锁屏幕时会被触发，我一直在文档中寻找这样的事件等，但我找不到它。

如果没有这样的事件，那么我们如何创建呢？

Answer 1

屏幕（un）锁定事件中的Xamarin C＃活动

你可以创建一个监听器类来监听android锁屏和解锁事件，使用广播来接收屏幕状态。

首先创建一个ScreenListener.cs：

public class ScreenListener
{
    private Context mContext;
    private ScreenBroadcastReceiver mScreenReceiver;
    private static ScreenStateListener mScreenStateListener;

    public ScreenListener(Context context)
    {
        mContext = context;
        mScreenReceiver = new ScreenBroadcastReceiver();
    }

    /**
     * screen BroadcastReceiver
     */
    private class ScreenBroadcastReceiver : BroadcastReceiver
    {
    private String action = null;

        public override void OnReceive(Context context, Intent intent)
        {
            action = intent.Action;
            if (Intent.ActionScreenOn == action)
            { // screen on
                mScreenStateListener.onScreenOn();
            }
            else if (Intent.ActionScreenOff == action)
            { // screen off
                mScreenStateListener.onScreenOff();
            }
            else if (Intent.ActionUserPresent == action)
            { // unlock
                mScreenStateListener.onUserPresent();
            }
        }
    }

/**
 * begin to listen screen state
 *
 * @param listener
 */
public void begin(ScreenStateListener listener)
{
    mScreenStateListener = listener;
    registerListener();
    getScreenState();
}

/**
 * get screen state
 */
private void getScreenState()
{
    PowerManager manager = (PowerManager)mContext
            .GetSystemService(Context.PowerService);
    if (manager.IsScreenOn)
    {
        if (mScreenStateListener != null)
        {
            mScreenStateListener.onScreenOn();
        }
    }
    else
    {
        if (mScreenStateListener != null)
        {
            mScreenStateListener.onScreenOff();
        }
    }
}

/**
 * stop listen screen state
 */
public void unregisterListener()
{
    mContext.UnregisterReceiver(mScreenReceiver);
}

/**
 * regist screen state broadcast
 */
private void registerListener()
{
    IntentFilter filter = new IntentFilter();
    filter.AddAction(Intent.ActionScreenOn);
    filter.AddAction(Intent.ActionScreenOff);
    filter.AddAction(Intent.ActionUserPresent);
    mContext.RegisterReceiver(mScreenReceiver, filter);
}

public interface ScreenStateListener
{// Returns screen status information to the caller
    void onScreenOn();

    void onScreenOff();

    void onUserPresent();
}
}

然后在MainActivity.cs中：

public class MainActivity : AppCompatActivity,ScreenStateListener
{
   ScreenListener mScreenListener;
   protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.activity_main);
        mScreenListener = new ScreenListener(this);
    }
   protected override void OnDestroy()
    {
        base.OnDestroy();
        mScreenListener.unregisterListener();
    }

   protected override void OnResume()
    {
        base.OnResume();
        mScreenListener.begin(this);

    }
   public void onScreenOn()
    {
        Console.WriteLine("onScreenOn");
    }

   public void onScreenOff()
    {
        Console.WriteLine("onScreenOff");
    }

   public void onUserPresent()
    {
        Console.WriteLine("onUserPresent");
    }


}

Answer 2

这是一个sample的Xamarin.Android活动生命周期。

您可以覆盖任何生命周期方法，如下所示：

protected override void OnResume() {
    base.OnResume(); 
}

就像在原生Android中一样，当系统将活动放入后台时，会触发OnPause。当活动准备好开始与用户交互时，将调用OnResume。

OnPause和OnResume可用于您的（非）锁定事件。