在Kotlin

假设A和B是活动，导航来自A -> B 我们需要A <- B的结果

in A

    // calling the Activity B
    resultLauncher.launch(Intent(requireContext(), B::class.java))

    // we get data in here from B
    private var resultLauncher =
    registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
        when (result.resultCode) {
            Activity.RESULT_OK -> {
                result.data?.getStringExtra("VALUE")?.let {
                    // data received here
                }
            }
            Activity.RESULT_CANCELED -> {
                // cancel or failure
            }
        }
    }

In B

    // Sending result value back to A
    if (success) {
       setResult(RESULT_OK, Intent().putExtra("VALUE", value))
    } else {
       setResult(RESULT_CANCELED)
    }

你的主要活动

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    findViewById(R.id.takeCam).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent=new Intent(getApplicationContext(),TakePhotoActivity.class);
            intent.putExtra("Mode","Take");
            startActivity(intent);
        }
    });
    findViewById(R.id.selectGal).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent=new Intent(getApplicationContext(),TakePhotoActivity.class);
            intent.putExtra("Mode","Gallery");
            startActivity(intent);
        }
    });
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

}

在第二个活动中显示

private static final int CAMERA_REQUEST = 1888;
private ImageView imageView;
private static final int MY_CAMERA_PERMISSION_CODE = 100;
private static final int PICK_PHOTO_FOR_AVATAR = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_take_photo);

    imageView=findViewById(R.id.imageView);

    if(getIntent().getStringExtra("Mode").equals("Gallery"))
    {
        pickImage();
    }
    else {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (checkSelfPermission(Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                requestPermissions(new String[]{Manifest.permission.CAMERA}, MY_CAMERA_PERMISSION_CODE);
            } else {
                Intent cameraIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                startActivityForResult(cameraIntent, CAMERA_REQUEST);
            }
        }
    }
}
public void pickImage() {
    Intent intent = new Intent(Intent.ACTION_PICK);
    intent.setType("image/*");
    startActivityForResult(intent, PICK_PHOTO_FOR_AVATAR);
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults)
{
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if (requestCode == MY_CAMERA_PERMISSION_CODE)
    {
        if (grantResults[0] == PackageManager.PERMISSION_GRANTED)
        {
            Intent cameraIntent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
            startActivityForResult(cameraIntent, CAMERA_REQUEST);
        }
        else
        {
            Toast.makeText(this, "Camera Permission Denied..", Toast.LENGTH_LONG).show();
        }
    }
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == CAMERA_REQUEST && resultCode == Activity.RESULT_OK) {
        Bitmap photo = (Bitmap) data.getExtras().get("data");
        imageView.setImageBitmap(photo);
    }
        if (requestCode == PICK_PHOTO_FOR_AVATAR && resultCode == Activity.RESULT_OK) {
            if (data == null) {
                Log.d("ABC","No Such Image Selected");
                return;
            }
            try {
                Uri selectedData=data.getData();
                Log.d("ABC","Image Pick-Up");
                imageView.setImageURI(selectedData);
                InputStream inputStream = getApplicationContext().getContentResolver().openInputStream(selectedData);
                Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                Bitmap bmp=MediaStore.Images.Media.getBitmap(getContentResolver(),selectedData);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch(IOException e){

            }
    }
}

如果你想用活动结果更新用户界面，你不能使用this.runOnUiThread(new Runnable(){}。这样做，UI不会刷新新值。相反，你可以这样做:

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (resultCode == RESULT_CANCELED) {
        return;
    }

    global_lat = data.getDoubleExtra("LATITUDE", 0);
    global_lng = data.getDoubleExtra("LONGITUDE", 0);
    new_latlng = true;
}

@Override
protected void onResume() {
    super.onResume();

    if(new_latlng)
    {
        PhysicalTagProperties.this.setLocation(global_lat, global_lng);
        new_latlng=false;
    }
}

这看起来很傻，但效果很好。

首先，你在第一个活动中使用startActivityForResult()和参数，如果你想从第二个活动发送数据到第一个活动，然后使用意图通过setResult()方法传递值，并在第一个活动中的onActivityResult()方法中获取数据。

这在Android上是一个非常常见的问题

它可以被分解成三个部分

开始活动B(发生在活动A中) 设置请求的数据(发生在活动B中) 接收请求的数据(发生在活动A中)

startActivity B

Intent i = new Intent(A.this, B.class);
startActivity(i);

设置请求数据

在这一部分中，您将决定在发生特定事件时是否要发回数据。

例如:在活动B中有一个EditText和两个按钮b1, b2。 单击按钮b1将数据发送回活动A。 单击按钮b2不会发送任何数据。

发送数据

b1......clickListener
{
    Intent resultIntent = new Intent();
    resultIntent.putExtra("Your_key", "Your_value");
    setResult(RES_CODE_A, resultIntent);
    finish();
}

不发送数据

b2......clickListener
{
   setResult(RES_CODE_B, new Intent());
   finish();
}

用户单击后退按钮

默认情况下，结果设置为Activity。RESULT_CANCEL响应代码

检索结果

重写onActivityResult方法

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (resultCode == RES_CODE_A) {

       // b1 was clicked
       String x = data.getStringExtra("RES_CODE_A");

    }
    else if(resultCode == RES_CODE_B){

       // b2 was clicked
    }
    else{
       // The back button was clicked
    }
}

从你的FirstActivity，使用startActivityForResult()方法调用SecondActivity。

例如:

int LAUNCH_SECOND_ACTIVITY = 1
Intent i = new Intent(this, SecondActivity.class);
startActivityForResult(i, LAUNCH_SECOND_ACTIVITY);

在你的SecondActivity中，设置你想返回给FirstActivity的数据。如果你不想返回，就不要设置任何。

例如:在SecondActivity中，如果你想发回数据:

Intent returnIntent = new Intent();
returnIntent.putExtra("result",result);
setResult(Activity.RESULT_OK,returnIntent);
finish();

如果你不想返回数据:

Intent returnIntent = new Intent();
setResult(Activity.RESULT_CANCELED, returnIntent);
finish();

现在在FirstActivity类中，为onActivityResult()方法编写以下代码。

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (requestCode == LAUNCH_SECOND_ACTIVITY) {
        if(resultCode == Activity.RESULT_OK){
            String result=data.getStringExtra("result");
        }
        if (resultCode == Activity.RESULT_CANCELED) {
            // Write your code if there's no result
        }
    }
} //onActivityResult

要在Kotlin中以更好的方式实现两个活动之间的数据传递，请参见“在活动之间传递数据的更好方式”。