Android textView 中 onCreate 方法的改变

我在main.xml上使用 Layout Editor创建了一个textview名称是textView1。
我想使用一个自定义的字体，所以我在onCreate方法中创建了下面的代码，但是好像不能识别textView1。

package com.mystraldesign.memorable;

import android.app.Activity;
import android.graphics.Typeface;
import android.os.Bundle;

public class MemorableActivity extends Activity 
{
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Typeface type = Typeface.createFromAsset(getAssets(),"fonts/optima.ttf"); 
        textView1.setTypeface(type);
    }
}

什么原因呢？

    TextView textView1=(TextView)findViewById(R.id.textView1);//mail.xml里这个textview的id
    Typeface type = Typeface.createFromAsset(getAssets(),"fonts/optima.ttf"); 
    textView1.setTypeface(type);

请初始化 TextView

public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      // Font path
      String fontPath = "fonts/optima.ttf";
      // text view label
      TextView textView1= (TextView) findViewById(R.id.name);
     // Loading Font Face
      Typeface tf = Typeface.createFromAsset(getAssets(), fontPath);
     // Applying font
      textView1.setTypeface(tf);
  }