android小白，做一个很简单的动作，第一个activity里面输入的内容传递到第二个activity的textview中去，但是报错如下
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
第一个activity
public class MainActivity extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void sendMessage3(View view){
Intent intent=new Intent(this,DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.edit_message);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
}
public final static String EXTRA_MESSAGE = "com.mycompany.myfirstapp.MESSAGE";
}
第二个activity
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent intent = getIntent();
String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
TextView tv = (TextView) findViewById(R.id.textView);
tv.setText(message);
// Set the text view as the activity layout
setContentView(R.layout.activity_display_message);
}
如果我把 tv.setText(message);这句话注销掉，不赋值，第二个页面就能正常打开。
android刚上手小白。。自己研究了半天没研究出什么原因，求大神解答，非常感谢
