为什么必须在onCreate中初始化对象？(Why must be objects initialized in onCreate?)

我有以下代码：

public class MainActivity extends Activity { TextView number=(TextView)findViewById(R.id.number2); TextView number2=(TextView)findViewById(R.id.number2); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); number.setText("Text"); number.setText("Text"); }

接下来是更多代码，但是当我运行它时会崩溃。

在这之后我试图在onCreate（）中初始化TextViews

public class MainActivity extends Activity { TextView number; TextView number2; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); number=(TextView)findViewById(R.id.number); number2=(TextView)findViewById(R.id.number2); number.setText("Text"); number.setText("Text"); }

它工作。为什么必须在onCreate中初始化对象？

I have the following code:

public class MainActivity extends Activity { TextView number=(TextView)findViewById(R.id.number2); TextView number2=(TextView)findViewById(R.id.number2); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); number.setText("Text"); number.setText("Text"); }

followed by more code, but when I run it it crashes.

After doing that i tried to initialize TextViews in onCreate()

public class MainActivity extends Activity { TextView number; TextView number2; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); number=(TextView)findViewById(R.id.number); number2=(TextView)findViewById(R.id.number2); number.setText("Text"); number.setText("Text"); }

and it worked. Why must objects be initialized in onCreate?