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);
                }
            });

补充Nishant的回答，返回活动结果的最佳方法是:

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

我遇到的问题

new Intent();

然后我发现正确的方法是使用

getIntent();

得到当前的意图。

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{

    }
}

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。

例子

为了在上下文中了解整个过程，这里有一个补充的答案。更多的解释请看我的完整回答。

MainActivity.java

public class MainActivity extends AppCompatActivity {

    // Add a different request code for every activity you are starting from here
    private static final int SECOND_ACTIVITY_REQUEST_CODE = 0;

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

    // "Go to Second Activity" button click
    public void onButtonClick(View view) {

        // Start the SecondActivity
        Intent intent = new Intent(this, SecondActivity.class);
        startActivityForResult(intent, SECOND_ACTIVITY_REQUEST_CODE);
    }

    // This method is called when the second activity finishes
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        // check that it is the SecondActivity with an OK result
        if (requestCode == SECOND_ACTIVITY_REQUEST_CODE) {
            if (resultCode == RESULT_OK) { // Activity.RESULT_OK

                // get String data from Intent
                String returnString = data.getStringExtra("keyName");

                // set text view with string
                TextView textView = (TextView) findViewById(R.id.textView);
                textView.setText(returnString);
            }
        }
    }
}

SecondActivity.java

public class SecondActivity extends AppCompatActivity {

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

    // "Send text back" button click
    public void onButtonClick(View view) {

        // get the text from the EditText
        EditText editText = (EditText) findViewById(R.id.editText);
        String stringToPassBack = editText.getText().toString();

        // put the String to pass back into an Intent and close this activity
        Intent intent = new Intent();
        intent.putExtra("keyName", stringToPassBack);
        setResult(RESULT_OK, intent);
        finish();
    }
}

对于那些在onActivityResult中有错误requestCode问题的人

如果你在Fragment中调用startActivityForResult()， requestCode会被拥有Fragment的Activity改变。

如果你想在你的活动中得到正确的resultCode，试试这个:

变化:

startActivityForResult(意图,1);:

getActivity()。startActivityForResult(意图,1);