java - 使用 getExtra() - NullPointerException

Question

我有一个带有 onItemClick 方法的 fragment ，在该方法中我调用另一个 Activity 并传递 id 参数:

public class MoviesListFragment extends Fragment {
  // some code
  listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                TextView mid = (TextView) view.findViewById(R.id.textID);
                Intent intent = new Intent(getActivity().getBaseContext(), InfoActivity.class);
                intent.putExtra("id", mid.getText());
                startActivity(intent);
            }
        });
}

因此，在另一个 Activity (InfoActivity.java)中，我试图获取id-value:

public class InfoActivity extends Activity {

    Intent intent = getIntent();
    private final String id = intent.getStringExtra("id");
    // some code

并在这一行获得异常:intent.getStringExtra("id");

我哪里出错了？

Answer 1

这段代码:

Intent intent = getIntent();
private final String id = intent.getStringExtra("id");

应该从 onCreate() 或类似方法内部调用，否则在创建 Activity 对象时、在将 Intent 传递给它之前调用它。