取消StartActivityForResult时如何获取Intent数据？手动取消后能否获取？

Great question! Let's break this down into two clear scenarios: handling intentional cancellations where you can pass data, and working around cases where the result Intent is missing entirely.

1. 获取主动取消时的Intent数据（常规场景） #

Whether you're using the old startActivityForResult() API or the newer Activity Result API, you can retrieve data after a cancellation—as long as you explicitly set the result Intent in the launched Activity before finishing it.

旧API (startActivityForResult()) #

In the launched Activity, when the user triggers a cancellation (like tapping a cancel button or pressing the back key), manually set RESULT_CANCELED along with your data-carrying Intent:

// TargetActivity: Handle cancel button click
findViewById(R.id.btn_cancel).setOnClickListener(v -> {
    Intent resultIntent = new Intent();
    resultIntent.putExtra("cancel_reason", "User tapped cancel");
    resultIntent.putExtra("partial_input", "Half-filled form data");
    setResult(Activity.RESULT_CANCELED, resultIntent);
    finish();
});

// Override back key to pass data too
@Override
public void onBackPressed() {
    Intent resultIntent = new Intent();
    resultIntent.putExtra("cancel_reason", "Back button pressed");
    setResult(Activity.RESULT_CANCELED, resultIntent);
    super.onBackPressed();
}

Then in your original Activity's onActivityResult():

@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == MY_REQUEST_CODE) {
        if (resultCode == Activity.RESULT_CANCELED) {
            if (data != null) {
                String reason = data.getStringExtra("cancel_reason");
                String partialInput = data.getStringExtra("partial_input");
                // Process the data here
            }
        }
    }
}

新Activity Result API (Recommended) #

The logic for the launched Activity stays the same. In your original Activity, register a callback to receive the result:

// OriginalActivity: Register the result callback
val activityLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
    if (result.resultCode == Activity.RESULT_CANCELED) {
        result.data?.let { intent ->
            val reason = intent.getStringExtra("cancel_reason")
            val partialInput = intent.getStringExtra("partial_input")
            // Handle the canceled data
        }
    }
}

// Launch the target Activity
activityLauncher.launch(Intent(this, TargetActivity::class.java))

2. 手动取消后无法获取Intent数据：有没有补救办法？ #

If the launched Activity finishes without calling setResult() (e.g., a bug, or the system kills it due to low memory), result.data will be null. But you can still retrieve data with these workarounds:

方案1：使用ViewModel共享数据（Same App, Recommended） #

If both Activities are in the same app, use a shared ViewModel to pass data without relying on the result Intent:

// Shared ViewModel class
class SharedCancelViewModel : ViewModel() {
    val canceledData = MutableLiveData<CancelData>() // CancelData is your custom data class
}

// TargetActivity: Store data when canceling
val viewModel = ViewModelProvider(requireActivity()).get(SharedCancelViewModel::class.java)
viewModel.canceledData.value = CancelData("Unexpected cancel", "User's partial input")
finish()

// OriginalActivity: Observe the shared data
val viewModel = ViewModelProvider(this).get(SharedCancelViewModel::class.java)
viewModel.canceledData.observe(this) { data ->
    // Access the canceled data here
}

方案2：用SharedPreferences Persist Data #

Save the data to SharedPreferences in the launched Activity, then read it in the original Activity's callback:

// TargetActivity: Save data on cancel
SharedPreferences sp = getSharedPreferences("cancel_data_store", MODE_PRIVATE);
sp.edit()
   .putString("reason", "No result Intent set")
   .putString("partial_input", "User's unfinished work")
   .apply();
finish();

// OriginalActivity: Retrieve data when result is missing
if (resultCode == Activity.RESULT_CANCELED && result.getData() == null) {
    SharedPreferences sp = getSharedPreferences("cancel_data_store", MODE_PRIVATE);
    String reason = sp.getString("reason", null);
    String partialInput = sp.getString("partial_input", null);
    // Process the data, then clear it to avoid conflicts next time
    sp.edit().clear().apply();
}

方案3：Local Database (For Complex Data) #

For large or structured data, use a local database like Room to temporarily store the data. The original Activity can query the database in the result callback and delete the temporary record afterward.

⚠️ Important Notes:

• Avoid static variables for data passing—they cause memory leaks, especially if the Activity is destroyed.
• When using SharedPreferences or databases, add unique identifiers (like a request ID) to avoid overwriting data from multiple launches.
• If the system kills the launched Activity, it can save state in onSaveInstanceState(), but the original Activity can't access this state directly—rely on pre-persisted data instead.

内容的提问来源于stack exchange，提问作者Shashikant Yadav