使用getExtra（） - NullPointerException

Question

我有一个onItemClick - 方法的片段，我在其中调用另一个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);
            }
        });
}

所以，在另一个活动（InfoActivity.java）中我试图获得id - 值：

public class InfoActivity extends Activity {

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

并在此行中获得例外：intent.getStringExtra("id");

我犯了错误？

Answer 1

此代码：

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对象之前调用它，然后将意图传递给它。

Answer 2

 private final String id;
 public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.table);
        Intent intent = getIntent();
         id = intent.getStringExtra("id");

    }