c# - Xamarin 安卓 C# : How to pass data back from activity without new intent

Question

我有一个 MainActivity，它会立即调用 SetContentView(到主屏幕)。按下按钮时，它会启动一个新的 Intent Activity 1，打开第二个屏幕并使用 PutExtra 将变量传输到它。

现在如果我想在按下按钮时返回主屏幕，Finish();是一种完美的方式，因为它会停止 activity1 并且我可以毫无问题地返回主屏幕。

虽然，当我想将变量传输回主屏幕时，我必须创建一个新的 Intent/Activity 来创建主屏幕的全新实例。

有没有办法在不创建主屏幕的新实例的情况下从第二个 Activity 传回数据？

主 Activity .cs

using System;
using System.Collections.Generic;
using Android.App;
using Android.Content;
using Android.Provider;
using Android.Views;
using Android.Widget;
using Android.OS;
using static Android.Renderscripts.ScriptGroup;
using Android.Preferences;

namespace App11
{
    [Activity(Label = "App11", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Android.App.Activity
    {
        //define all variables

        IList<String> listitems = new List<String>();

        public static int putposition;

        public static string putname;

        public static int getposition;

        public static string getname;

        bool edittoggle = false;

        int count = 1;

        protected override void OnCreate(Bundle bundle)
        {
            //create screen
            base.OnCreate(bundle);

            SetContentView(Resource.Layout.Main);

            ActionBar.Hide();


            //get/define widgets from screen
            TextView text_title = FindViewById<TextView>(Resource.Id.Text_Title);
            ListView list_schedule = FindViewById<ListView>(Resource.Id.List_Schedule);
            ImageButton buttonadditem = FindViewById<ImageButton>(Resource.Id.Button_AddItem);
            ImageButton buttonedititem = FindViewById<ImageButton>(Resource.Id.Button_EditItem);
            ImageButton buttonsettings = FindViewById<ImageButton>(Resource.Id.Button_Settings);

            //define array
            ArrayAdapter adapter = new ArrayAdapter<String>(this, Android.Resource.Layout.SimpleListItem1, listitems);
            list_schedule.Adapter = adapter;


            //on additem click
            FindViewById<ImageButton>(Resource.Id.Button_AddItem).Click += delegate { adapter.Add("Alarm Item " + count++); };

            //on edititem click
            FindViewById<ImageButton>(Resource.Id.Button_EditItem).Click += delegate
            {
                //toggle
                if (edittoggle == true)
                {
                    edittoggle = false;
                }
                else
                {
                    edittoggle = true;
                }
            };

                //on list item click
            list_schedule.ItemClick += (s, e) =>
            {

                //if edititem button is toggled on
                if (edittoggle == true)
                {
                    //create new intent activity1
                    Intent activity1 = new Intent(this, typeof(Activity1));

                    //put position of item from list
                    putname = (String)adapter.GetItem(e.Position);
                    activity1.PutExtra("Main_Put_Edit_Name", putname);
                    Console.WriteLine("put int edit name = " + putname);

                    //put name of item from list
                    putposition = e.Position;
                    activity1.PutExtra("Main_Put_Edit_Position", putposition);
                    Console.WriteLine("put string edit position = " + putposition);

                    StartActivityForResult(activity1, 0);
                }
                else
                {
                    //TODO: show settings
                }

            };


            protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
            {
                base.OnActivityResult(requestCode, resultCode, data);
                if (resultCode == Result.Ok)
                {
                    getname = data.GetStringExtra("Main_Put_Edit_Name2");
                    Console.WriteLine("get int edit name = " + getname);
                    getposition = data.GetIntExtra("Main_Put_Edit_Position2", 0);
                    Console.WriteLine("get int edit position = " + getposition);
                    //put_name and put_position should now hold the results you want, you can do whatever you want with these two values now in your MainActivity
                    Console.WriteLine("test = " + listitems[0]);
                    //but now range is out of bounds because listitems is only properly defined in OnCreate
                }
            }
        }
    }
}

Activity1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.Provider;
using static Android.Renderscripts.ScriptGroup;
using Android.Preferences;

namespace App11
{

    [Activity(Label = "Activity1")]
    public class Activity1 : Android.App.Activity
    {

        //define variables

        IList<string> listitems = new List<string>();

        public static int get_position;

        public static string get_name;

        protected override void OnCreate(Bundle bundle)
        {
            //create screen
            base.OnCreate(bundle);

            SetContentView(Resource.Layout.layout1);

            ActionBar.Hide();


            //define screen widgets
            ListView list_schedule2 = FindViewById<ListView>(Resource.Id.List_Schedule2);
            EditText alarm_name = FindViewById<EditText>(Resource.Id.name_input);
            Button donebutton = FindViewById<Button>(Resource.Id.button_done);

            //get extras from activity1
            get_position = Intent.GetIntExtra("Main_Put_Edit_Position", 0);
            Console.WriteLine("get array edit position = " + get_position);

            get_name = Intent.GetStringExtra("Main_Put_Edit_Name");
            Console.WriteLine("get array edit name = " + get_name);

            //just cuz
            alarm_name.Text = get_name;


            ArrayAdapter adapter = new ArrayAdapter<String>(this, Android.Resource.Layout.SimpleListItem1, listitems);
            list_schedule2.Adapter = adapter;


            FindViewById<Button>(Resource.Id.button_done).Click += delegate
            {
                //create new intent
                Intent intent = new Intent(); //Added the type of Main Activity

                int put_position = get_position;
                intent.PutExtra("Main_Put_Edit_Position2", put_position);
                Console.WriteLine("put array edit position = " + put_position);

                string put_name = alarm_name.Text;
                intent.PutExtra("Main_Put_Edit_Name2", put_name);
                Console.WriteLine("put array edit name = " + put_name);

                SetResult(Result.Ok, intent); //added the SetResult method.
                Finish();
            };
        }
    }
}

我现在只是用 int 和 string 测试它。放置/获取列表项的位置(整数)和名称(字符串)。

Answer 1

根据 Xamarin Official Documentation有一种方法可以将数据从第二个 Activity 传回给第一个启动它的 Activity 。

关键是要用StartActivityForResult从第一个 Activity 启动第二个 Activity ，并使用 SetResult在 Finish() 之前的第二个 Activity 中方法将结果发送回第一个 Activity 。

正如您在我上面发布的链接中看到的那样，它使用起来简单直接。

您可以使用以下代码从第一个 Activity 中开始您的第二个 Activity :

var myIntent = new Intent (this, typeof(SecondActivity));
StartActivityForResult (myIntent, 0);

在您的第二个 Activity 中，当您希望它以一组结果结束时，您可以使用以下代码:

Intent myIntent = new Intent (this, typeof(FirstActivity));
myIntent.PutExtra ("greeting", "Hello from the Second Activity!");
SetResult (Result.Ok, myIntent);
Finish();

为了检索发送回第一个 Activity 的结果，您必须使用此代码:

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
    base.OnActivityResult(requestCode, resultCode, data);
    if (resultCode == Result.Ok) {
        string stringRetFromResult = data.GetStringExtra("greeting");
        //stringRetFromResult should hold now the value of 'Hello from the Second Activity!'
    }
}

更新

根据您发布的代码，我假设您想在这部分代码中将结果发回:

FindViewById<Button>(Resource.Id.button_done).Click += delegate
{
    ...
};

试试这个:

FindViewById<Button>(Resource.Id.button_done).Click += delegate
    Intent intent = new Intent(this, typeof(MainActivity); //Added the type of Main Activity
    int put_position = get_position;
    intent.PutExtra("Main_Put_Edit_Position2", put_position);
    Console.WriteLine("put array edit position = " + put_position);
    string put_name = alarm_name.Text;
    intent.PutExtra("Main_Put_Edit_Name2", put_name);
    Console.WriteLine("put array edit name = " + put_name);
    SetResult(Result.Ok, intent); //added the SetResult method.
    Finish();
};

除此之外，在您的第一个 Activity 中，更改 StartActivity(activity1);至 StartActivityForResult(activity1, 0);并且您必须将此代码添加到您的主要 Activity 中:

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
    base.OnActivityResult(requestCode, resultCode, data);
    if (resultCode == Result.Ok) {
        string put_name = data.GetStringExtra("Main_Put_Edit_Name2");
        int put_position = data.GetIntExtra("Main_Put_Edit_Position2");
        //put_name and put_position should now hold the results you want, you can do whatever you want with these two values now in your MainActivity
    }
}