intent.getStringExtra始终为"null“

Intent intent = new Intent(MainActivity.this, SecondActivity.class);
intent.putExtra("key_name", "value_string");
startActivity(intent);

String value = getIntent().getStringExtra("key_name");

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

    Intent intent = getIntent();
    String value = intent.getStringExtra("key_name");
}

String value = "value_string";
intent.putExtra("key_name", value);

String value = getActivity().getIntent().getStringExtra("key_name");