如何将Android一个Activity的ImageView图片设为另一个Activity背景？

我开发的Android应用包含两个Activity，希望将其中一个Activity的背景设置为另一个Activity内ImageView展示的图片，尝试实现但未达预期效果，以下是我的代码，请帮忙审核并指导正确实现方式：

获取ImageView的Activity（GallerySaver）代码： #

using Android.App;
using Android.Content;
using Android.OS;
using Android.Provider;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using Android.Graphics;

using SQLite;

namespace HAMANIA_APP
{
    [Activity(Label = "GallerySaver")]
    public class GallerySaver : Activity
    {
        Button camera, save, uploadPhoto;
        ImageView pic;
        Bitmap bitmap;
        bool mExternalStorageAvailable = false;
        bool mExternalStorageWriteable = false;
        public static readonly int imageid = 1000;

        

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.Phone_Gallery_Saver);
            camera = FindViewById<Button>(Resource.Id.btnCamera);
            save = FindViewById<Button>(Resource.Id.btnSave);
            pic = FindViewById<ImageView>(Resource.Id.gallery);
            save.Click += Save_Click;
            camera.Click += Camera_Click;
            


            // Create your application here
        }

        

        private void Save_Click(object sender, EventArgs e)
        {
            Intent inte = new Intent();
            inte.SetType("image/*");
            inte.SetAction(Intent.ActionGetContent);
            StartActivityForResult(Intent.CreateChooser(inte, "Select Picture"), imageid);

            Toast.MakeText(Application.Context, "Image saved to gallery", ToastLength.Long).Show();
        }

        private void Camera_Click(object sender, EventArgs e)
        {
            Intent intent = new Intent(MediaStore.ActionImageCapture);
            StartActivityForResult(intent, 0);
        }
        protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
        {
            base.OnActivityResult(requestCode, resultCode, data);
            if (requestCode == 0)//coming from camera
            {
                if (resultCode == Result.Ok)
                {
                    Bundle extras = data.Extras;
                    bitmap = (Bitmap)extras.Get("data");
                    pic.SetImageBitmap(bitmap);
                    //bitmap = (Android.Graphics.Bitmap)data.Extras.Get("data");
                    // pic.SetImageBitmap(bitmap);
                    
                }
                
                }else
                {
                    if ((requestCode == imageid) && (resultCode == Result.Ok) && (data != null))
                    {
                        Android.Net.Uri uri = data.Data;
                        bitmap = MediaStore.Images.Media.GetBitmap(ContentResolver, uri);
                        pic.SetImageBitmap(bitmap);
                    var image = (Bitmap)data.Extras.Get("data");

                    

                }
            }
        }

        
    }
}

需要设置背景的Activity（MenuActivity）代码： #

using Android.App;
using Android.Content;
using Android.Graphics;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Xamarin.Essentials;
using Android.Provider;
using Java.IO;
using System.IO;
using Android.Net;
using AndroidX.Core.Content;
using Android.Graphics.Drawables;

namespace HAMANIA_APP
{
    [Activity(Label = "MenuActivity")]
    public class MenuActivity : Activity
    {
        Button camera, gallery, control;
        BroadcastBattery broadcastBattery;
        TextView tv;
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.Menu);
            camera = FindViewById<Button>(Resource.Id.BLUETOOTH);
            tv = FindViewById<TextView>(Resource.Id.tv);
            broadcastBattery = new BroadcastBattery(tv);
            control = FindViewById<Button>(Resource.Id.control);
            control.Click += Control_Click;
            gallery = FindViewById<Button>(Resource.Id.gallery);
            camera.Click += Camera_Click;
           
        }

        public static string BackgroundImagePath { get; set; }


        private void Control_Click(object sender, EventArgs e)
        {
            Intent intent = new Intent(this, typeof(ControlCenter));
            StartActivity(intent);
        }

        private void Camera_Click(object sender, EventArgs e)
        {
            Intent intent2 = new Intent(this, typeof(GallerySaver));
            StartActivity(intent2);
        }

        
    }
}

正确实现方案 #

核心思路是将GallerySaver中选中/拍摄的图片传递给MenuActivity，推荐使用保存图片到应用私有目录+传递文件路径的方式，避免Bitmap直接传递的内存限制问题，具体步骤如下：

1. 改造GallerySaver，保存图片并返回路径 #

在GallerySaver类中添加保存Bitmap到本地的方法：

// 保存Bitmap到应用私有图片目录
private string SaveBitmapToFile(Bitmap bitmap)
{
    var dir = Application.Context.GetExternalFilesDir(Android.OS.Environment.DirectoryPictures);
    if (!dir.Exists) dir.Mkdirs();
    
    var fileName = $"bg_{DateTime.Now.Ticks}.png";
    var filePath = Path.Combine(dir.AbsolutePath, fileName);
    
    using (var stream = new FileStream(filePath, FileMode.Create))
    {
        bitmap.Compress(Bitmap.CompressFormat.Png, 100, stream);
        stream.Flush();
    }
    return filePath;
}

修改OnActivityResult方法，在设置ImageView后保存图片并将路径返回给MenuActivity：

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
    base.OnActivityResult(requestCode, resultCode, data);
    string imagePath = null;

    if (requestCode == 0)// 相机返回
    {
        if (resultCode == Result.Ok)
        {
            Bundle extras = data.Extras;
            bitmap = (Bitmap)extras.Get("data");
            pic.SetImageBitmap(bitmap);
            imagePath = SaveBitmapToFile(bitmap);
        }
    }
    else if ((requestCode == imageid) && (resultCode == Result.Ok) && (data != null))// 相册返回
    {
        Android.Net.Uri uri = data.Data;
        bitmap = MediaStore.Images.Media.GetBitmap(ContentResolver, uri);
        pic.SetImageBitmap(bitmap);
        imagePath = SaveBitmapToFile(bitmap);
    }

    // 返回路径给MenuActivity
    if (!string.IsNullOrEmpty(imagePath))
    {
        Intent resultIntent = new Intent();
        resultIntent.PutExtra("BackgroundPath", imagePath);
        SetResult(Result.Ok, resultIntent);
        Finish(); // 关闭当前Activity回到MenuActivity
    }
}

2. 改造MenuActivity，接收路径并设置背景 #

修改MenuActivity中启动GallerySaver的方式，改用StartActivityForResult：

private void Camera_Click(object sender, EventArgs e)
{
    Intent intent2 = new Intent(this, typeof(GallerySaver));
    StartActivityForResult(intent2, 1001); // 自定义请求码
}

重写OnActivityResult接收路径并设置背景：

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
    base.OnActivityResult(requestCode, resultCode, data);

    if (requestCode == 1001 && resultCode == Result.Ok && data != null)
    {
        string imagePath = data.GetStringExtra("BackgroundPath");
        if (!string.IsNullOrEmpty(imagePath))
        {
            Bitmap bitmap = BitmapFactory.DecodeFile(imagePath);
            Drawable background = new BitmapDrawable(Resources, bitmap);
            Window.DecorView.SetBackground(background);
            
            // 保存路径，下次启动自动加载
            BackgroundImagePath = imagePath;
        }
    }
}

如果需要启动时自动加载上次设置的背景，在OnCreate中添加：

protected override void OnCreate(Bundle savedInstanceState)
{
    base.OnCreate(savedInstanceState);
    SetContentView(Resource.Layout.Menu);
    // ... 原有初始化代码

    // 加载保存的背景
    if (!string.IsNullOrEmpty(BackgroundImagePath))
    {
        Bitmap bitmap = BitmapFactory.DecodeFile(BackgroundImagePath);
        if (bitmap != null)
        {
            Drawable background = new BitmapDrawable(Resources, bitmap);
            Window.DecorView.SetBackground(background);
        }
    }
}

注意事项 #

• 相机默认返回的是缩略图，若需要原图，建议通过指定文件路径的方式调用相机。
• 使用应用私有存储目录无需申请外部存储权限，适配Android 10+的权限规则。
• 处理完Bitmap后可调用bitmap.Recycle()释放内存，避免泄漏。

内容的提问来源于stack exchange，提问作者Rom Yannay