[C] Added ability to predefine value to prompt (xamarin#8362) fixes x…

…amarin#8346

* Added ability to predefine value

* Prevent ABI break

* Update Issue6713.cs

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue6713.cs

@@ -7,6 +7,8 @@ namespace Xamarin.Forms.Controls.Issues
 	[Issue(IssueTracker.Github, 6713, "[Enhancement] Display prompts", PlatformAffected.iOS | PlatformAffected.Android)]
 	public class Issue6713 : TestContentPage // or TestMasterDetailPage, etc ...
 	{
+		const string PrefilledValue = "1337";
+
 		protected override void Init()
 		{
 			var scrollView = new ScrollView();
@@ -22,7 +24,7 @@ protected override void Init()
 			var button = new Button { Text = "Default keyboard" };
 			button.Clicked += async (sender, e) =>
 			{
-				var result = await DisplayPromptAsync("What’s the most useless product around today?", "The USB pet rock is definitely up there. What items do you have a hard time believing they actually exist?");
+				var result = await DisplayPromptAsync("What’s the most useless product around today?", "The USB pet rock is definitely up there. What items do you have a hard time believing they actually exist?", initialValue: "");
 
 				if (result != null)
 					(sender as Button).Text = result;
@@ -32,13 +34,23 @@ protected override void Init()
             var button2 = new Button { Text = "Numeric keyboard" };
             button2.Clicked += async (sender, e) =>
             {
-	            var result = await DisplayPromptAsync("What’s the meaning of life?", "You know that number.", maxLength:2, keyboard:Keyboard.Numeric);
+	            var result = await DisplayPromptAsync("What’s the meaning of life?", "You know that number.", maxLength:2, keyboard:Keyboard.Numeric, initialValue: "");
 
 	            if (result != null)
 					(sender as Button).Text = result;
 			};
             stackLayout.Children.Add(button2);
 
+			var button3 = new Button { Text = "Prefilled" };
+			button3.Clicked += async (sender, e) =>
+			{
+				var result = await DisplayPromptAsync("The input field should have a value already", $"And it should be {PrefilledValue}", initialValue: PrefilledValue);
+
+				if (result != null)
+					(sender as Button).Text = result;
+			};
+			stackLayout.Children.Add(button3);
+
 			scrollView.Content = stackLayout;
 			Content = scrollView;
 		}

Xamarin.Forms.Core/Page.cs

@@ -209,9 +209,16 @@ public Task<bool> DisplayAlert(string title, string message, string accept, stri
 			return args.Result.Task;
 		}
 
+		[Obsolete("DisplayPromptAsync overload is obsolete as of version 4.5.0 and is no longer supported.")]
+		[EditorBrowsable(EditorBrowsableState.Never)]
 		public Task<string> DisplayPromptAsync(string title, string message, string accept = "OK", string cancel = "Cancel", string placeholder = null, int maxLength = -1, Keyboard keyboard = default(Keyboard))
 		{
-			var args = new PromptArguments(title, message, accept, cancel, placeholder, maxLength, keyboard);
+			return DisplayPromptAsync(title, message, accept, cancel, placeholder, maxLength, keyboard, "");
+		}
+
+		public Task<string> DisplayPromptAsync(string title, string message, string accept = "OK", string cancel = "Cancel", string placeholder = null, int maxLength = -1, Keyboard keyboard = default(Keyboard), string initialValue = "")
+		{
+			var args = new PromptArguments(title, message, accept, cancel, placeholder, maxLength, keyboard, initialValue);
 			MessagingCenter.Send(this, PromptSignalName, args);
 			return args.Result.Task;
 		}

Xamarin.Forms.Core/PromptArguments.cs

@@ -1,18 +1,26 @@
-using System.ComponentModel;
+using System;
+using System.ComponentModel;
 using System.Threading.Tasks;
 
 namespace Xamarin.Forms.Internals
 {
 	[EditorBrowsable(EditorBrowsableState.Never)]
 	public class PromptArguments
 	{
+		[Obsolete("PromptArguments overload is obsolete as of version 4.5.0 and is no longer supported.")]
+		[EditorBrowsable(EditorBrowsableState.Never)]
 		public PromptArguments(string title, string message, string accept = "OK", string cancel = "Cancel", string placeholder = null, int maxLength = -1, Keyboard keyboard = default(Keyboard))
+			: this (title, message, accept, cancel, placeholder, maxLength, keyboard, "")
+		{ }
+
+		public PromptArguments(string title, string message, string accept = "OK", string cancel = "Cancel", string placeholder = null, int maxLength = -1, Keyboard keyboard = default(Keyboard), string initialValue = "")
 		{
 			Title = title;
 			Message = message;
 			Accept = accept;
 			Cancel = cancel;
 			Placeholder = placeholder;
+			InitialValue = initialValue;
 			MaxLength = maxLength;
 			Keyboard = keyboard ?? Keyboard.Default;
 			Result = new TaskCompletionSource<string>();
@@ -28,6 +36,8 @@ public PromptArguments(string title, string message, string accept = "OK", strin
 
 		public string Placeholder { get; }
 
+		public string InitialValue { get; }
+
 		public int MaxLength { get; }
 
 		public Keyboard Keyboard { get; }

Xamarin.Forms.Platform.Android/PopupManager.cs

@@ -141,7 +141,7 @@ void OnPromptRequested(Page sender, PromptArguments arguments)
 				alertDialog.SetMessage(arguments.Message);
 
 				var frameLayout = new FrameLayout(Activity);
-				var editText = new EditText(Activity) { Hint = arguments.Placeholder };
+				var editText = new EditText(Activity) { Hint = arguments.Placeholder, Text = arguments.InitialValue };
 				var layoutParams = new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MatchParent, ViewGroup.LayoutParams.WrapContent)
 				{
 					LeftMargin = (int)(22 * Activity.Resources.DisplayMetrics.Density),

Xamarin.Forms.Platform.iOS/Platform.cs

@@ -366,6 +366,7 @@ void PresentPrompt(PromptArguments arguments)
 			alert.AddTextField(uiTextField =>
 			{
 				uiTextField.Placeholder = arguments.Placeholder;
+				uiTextField.Text = arguments.InitialValue;
 				uiTextField.ShouldChangeCharacters = (field, range, replacementString) => arguments.MaxLength <= -1 || field.Text.Length + replacementString.Length - range.Length <= arguments.MaxLength;
 				uiTextField.ApplyKeyboard(arguments.Keyboard);
 			});