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){

            }
    }
}

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。

我将在简短的回答中发布Android X的新“方式”(因为在某些情况下，你不需要自定义注册表或合同)。如需详细信息，请参见:从活动获取结果

重要提示:Android X的向后兼容性存在bug，所以你必须在Gradle文件中添加fragment_version。否则你会得到一个异常“新结果API错误:只能使用低16位的requestCode”。

dependencies {

    def activity_version = "1.2.0-beta01"
    // Java language implementation
    implementation "androidx.activity:activity:$activity_version"
    // Kotlin
    implementation "androidx.activity:activity-ktx:$activity_version"

    def fragment_version = "1.3.0-beta02"
    // Java language implementation
    implementation "androidx.fragment:fragment:$fragment_version"
    // Kotlin
    implementation "androidx.fragment:fragment-ktx:$fragment_version"
    // Testing Fragments in Isolation
    debugImplementation "androidx.fragment:fragment-testing:$fragment_version"
}

现在你只需要添加活动的成员变量。这使用预定义的注册表和通用契约。

public class MyActivity extends AppCompatActivity{

   ...

    /**
     * Activity callback API.
     */
    // https://developer.android.com/training/basics/intents/result
    private ActivityResultLauncher<Intent> mStartForResult = registerForActivityResult(new ActivityResultContracts.StartActivityForResult(),

            new ActivityResultCallback<ActivityResult>() {

                @Override
                public void onActivityResult(ActivityResult result) {
                    switch (result.getResultCode()) {
                        case Activity.RESULT_OK:
                            Intent intent = result.getData();
                            // Handle the Intent
                            Toast.makeText(MyActivity.this, "Activity returned ok", Toast.LENGTH_SHORT).show();
                            break;
                        case Activity.RESULT_CANCELED:
                            Toast.makeText(MyActivity.this, "Activity canceled", Toast.LENGTH_SHORT).show();
                            break;
                    }
                }
            });

在新API之前，你有:

btn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MyActivity .this, EditActivity.class);
                startActivityForResult(intent, Constants.INTENT_EDIT_REQUEST_CODE);
            }
        });

您可能注意到请求代码现在由谷歌框架生成(并保持)。 你的代码变成:

 btn.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    Intent intent = new Intent(MyActivity .this, EditActivity.class);
                    mStartForResult.launch(intent);
                }
            });

如何检查主要活动的结果?

你需要重写Activity.onActivityResult()，然后检查它的参数:

requestCode标识哪个应用程序返回了这些结果。这是在调用startActivityForResult()时由您定义的。 resultCode告诉你这个应用程序是成功了、失败了还是其他什么 data保存此应用程序返回的任何信息。这可能是空的。

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
    }
}

你需要重写Activity.onActivityResult():

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

    if (resultCode == RESULT_CODE_ONE) {

       String a = data.getStringExtra("RESULT_CODE_ONE");

    }
    else if(resultCode == RESULT_CODE_TWO){

       // b was clicked
    }
    else{

    }
}