Why is onActivityResult is called before a contact is chosen?

问题

I'm following the answer https://stackoverflow.com/a/867828/129805 to add a contact picker to my app.

The problem is that onActivityResult is immediately invoked with the correct reqCode (PICK_CONTACT), but with aresultCode of 0 and a null for data.

It is not invoked again, when the user actually picks a contact.

The AndroidManifest gives this activity android:launchMode="singleInstance"> as I only ever want there to be one instance.

What have I done wrong?

MainActivity.java:

@Override
protected void onCreate(Bundle savedInstanceState) {
    ...
    addContactButton = (Button) findViewById(R.id.addContactButton);
    addContactButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(Intent.ACTION_PICK, ContactsContract.Contacts.CONTENT_URI);
            startActivityForResult(intent, PICK_CONTACT);
        }
    });
}

@Override
public void onActivityResult(int reqCode, int resultCode, Intent data) {
    Log.d(TAG, "onActivityResult");
    super.onActivityResult(reqCode, resultCode, data);

    switch (reqCode) {
        case (PICK_CONTACT) :
            if (resultCode == Activity.RESULT_OK) {
                Uri contactData = data.getData();
                Cursor c =  getContentResolver().query(contactData, null, null, null, null);
                if (c.moveToFirst()) {
                    String name = c.getString(c.getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME));
                    // TODO Whatever you want to do with the selected contact name.
                    Log.d(TAG, "you chose " + name + ".");
                }
            }
            break;
    }
}

回答1:

The singleInstance fires the callback immediately. You have more info in this link

来源：https://stackoverflow.com/questions/32644502/why-is-onactivityresult-is-called-before-a-contact-is-chosen