Xamarin Alert | Pop-ups

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Xamarin 相关官方文档

Displaying Pop-ups

简单用法：

DisplayAlert ("Alert", "You have been alerted", "OK");

又返回结果的 Alert:

var answer = await DisplayAlert("Exit", "Do you wan't to exit the App?", "Yes", "No");
if (answer)
{// User choose Yes
}
else
{// User choose No
}

进阶版 Alert

用 DisplayAlert 显示下载的状态，随着下载状态自行修改 DisplayAlert text

Here is a simple “Dynamic Alert” for Forms and iOS using UIAlertController and Android using a DialogFragment and a Xamarin.Forms dependency service:

Dependency Interface:

public interface IDynamicAlert
{void Show(string title, string message);void Update(string message);void Dismiss();
}

iOS `IDynamicAlert` Dependency Implementation:

public class DynamicAlert : IDynamicAlert
{UIAlertController alert;public void Show(string title, string message){if (alert != null) throw new Exception("DynamicAlert already showing");alert = UIAlertController.Create(title, message, UIAlertControllerStyle.Alert);var rootVC = UIApplication.SharedApplication.Windows[0].RootViewController;rootVC.PresentViewController(alert, true, () =>{});}public void Update(string message){if (alert == null) throw new Exception("DynamicAlert is not showing, call Show first");alert.Message = message;}public void Dismiss(){if (alert == null) throw new Exception("DynamicAlert is not showing, call Show first");alert.DismissViewController(true, () =>{alert.Dispose();alert = null;});}
}

Example Usage:

var alert = DependencyService.Get<IDynamicAlert>();
if (alert != null)
{alert.Show("StackOverflow", "Starting your request...");await Task.Delay(2000); // Do some work...alert.Update("Your request is processing...");await Task.Delay(2000); // Do some work...alert.Update("Your request is complete...");await Task.Delay(750);alert.Dismiss();
}
else
{throw new Exception("IDynamicAlert Dependency not found");
}

Output:

enter image description here

Android Version:

The android version consists of a couple of parts, a DialogFragment subclass and the IDynamicAlert implementation that uses the custom DialogFragment.

Android DialogFragment Subclass:

public class DynamicAlertDialogFragment : DialogFragment
{AlertDialog alertDialog;readonly Context context;public static DynamicAlertDialogFragment Instance(Context context, string title, string message){var fragment = new DynamicAlertDialogFragment(context);Bundle bundle = new Bundle();bundle.PutString("title", title);bundle.PutString("message", message);fragment.Arguments = bundle;return fragment;}public DynamicAlertDialogFragment(Context context){this.context = context;}public override Dialog OnCreateDialog(Bundle savedInstanceState){var title = Arguments.GetString("title");var message = Arguments.GetString("message");alertDialog = new AlertDialog.Builder(context).SetIcon(Android.Resource.Drawable.IcDialogInfo).SetTitle(title).SetMessage(message).Create();return alertDialog;}public void SetMessage(string message){(context as Activity).RunOnUiThread(() => { alertDialog.SetMessage(message);});}
}

Android `IDynamicAlert` Dependency Implementation:

public class DynamicAlert : IDynamicAlert
{const string FRAGMENT_TAG = "DynamicAlert_Fragment";DynamicAlertDialogFragment fragment;static FormsAppCompatActivity currentActivity;public static FormsAppCompatActivity CurrentActivity { set { currentActivity = value; } }public void Show(string title, string message){if (currentActivity == null) throw new Exception("DynamicAlert.CurrentActivity needs assigned");var fragMgr = currentActivity.FragmentManager;var fragTransaction = fragMgr.BeginTransaction();var previous = fragMgr.FindFragmentByTag(FRAGMENT_TAG);if (previous != null){fragTransaction.Remove(previous);}fragTransaction.DisallowAddToBackStack();fragment = DynamicAlertDialogFragment.Instance(currentActivity, title, message);fragment.Show(fragMgr, FRAGMENT_TAG);}public void Update(string message){if (fragment == null) throw new Exception("DynamicAlert is not showing, call Show first");fragment.SetMessage(message);}public void Dismiss(){if (fragment == null) throw new Exception("DynamicAlert is not showing, call Show first");fragment.Dismiss();fragment.Dispose();fragment = null;}
}

Android Init / Usage:

When creating the AlertDialog in the DialogFragment we need access to the current Activity and when using Xamarin.Forms, that is normally the MainActivity that is a FormsAppCompatActivity subclass. Thus you will need to initialize the DynamicAlert.CurrentActivity static property with this Activity in your MainActivity.OnCreate subclass:

Example:

protected override void OnCreate(Bundle bundle)
{TabLayoutResource = Resource.Layout.Tabbar;ToolbarResource = Resource.Layout.Toolbar;base.OnCreate(bundle);DynamicAlert.CurrentActivity = this;global::Xamarin.Forms.Forms.Init(this, bundle);LoadApplication(new App());

}