NullPointerException空指针异常——没有事先加载布局文件到acitivy——缺少：setContentView(R.layout.activity_setup_over);

空指针异常：

04-27 01:13:57.270: E/AndroidRuntime(4942): FATAL EXCEPTION: main
04-27 01:13:57.270: E/AndroidRuntime(4942): Process: com.itheima.mobilesafe74, PID: 4942
04-27 01:13:57.270: E/AndroidRuntime(4942): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.itheima.mobilesafe74/com.itheima.mobilesafe74.activity.SetupOverActivity}: java.lang.NullPointerException
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.os.Handler.dispatchMessage(Handler.java:102)
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.os.Looper.loop(Looper.java:136)
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.app.ActivityThread.main(ActivityThread.java:5017)
04-27 01:13:57.270: E/AndroidRuntime(4942): at java.lang.reflect.Method.invokeNative(Native Method)
04-27 01:13:57.270: E/AndroidRuntime(4942): at java.lang.reflect.Method.invoke(Method.java:515)
04-27 01:13:57.270: E/AndroidRuntime(4942): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-27 01:13:57.270: E/AndroidRuntime(4942): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-27 01:13:57.270: E/AndroidRuntime(4942): at dalvik.system.NativeStart.main(Native Method)
04-27 01:13:57.270: E/AndroidRuntime(4942): Caused by: java.lang.NullPointerException
04-27 01:13:57.270: E/AndroidRuntime(4942): at com.itheima.mobilesafe74.activity.SetupOverActivity.initUI(SetupOverActivity.java:46)
04-27 01:13:57.270: E/AndroidRuntime(4942): at com.itheima.mobilesafe74.activity.SetupOverActivity.onCreate(SetupOverActivity.java:38)
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.app.Activity.performCreate(Activity.java:5231)
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-27 01:13:57.270: E/AndroidRuntime(4942): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)

相应代码：

 package com.itheima.mobilesafe74.activity;

 import com.itheima.mobilesafe74.R;
 import com.itheima.mobilesafe74.utils.ConstentValue;
 import com.itheima.mobilesafe74.utils.SpUtil;
 import android.app.Activity;
 import android.content.Intent;
 import android.os.Bundle;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.TextView;

 /**
  * 说明 :手机安全导航设置完成的界面
  */
 public class SetupOverActivity extends Activity
 {
     @Override
     protected void onCreate(Bundle savedInstanceState)
     {
         super.onCreate(savedInstanceState);
 //        setContentView(R.layout.activity_setup_over);
         boolean setup_over = SpUtil.getBoolean(this, ConstentValue.SETUP_OVER,
                 false);
         if (setup_over)
         {
             // 手机安全导航设置完成跳转到设置完成的界面
             setContentView(R.layout.activity_setup_over);
         } else
         {
             // 手机安全导航设置没有完成跳转到导航设置1的界面
             Intent intent = new Intent(this, Setup1Activity.class);
             startActivity(intent);
             // 跳转到一个新的界面时需要关闭当前界面
             finish();
         }
         initUI();
     }

     private void initUI()
     {

         TextView tv_safe_number = (TextView) findViewById(R.id.tv_safe_number);
         String phone = SpUtil.getString(this, ConstentValue.CONTACT_PHONE, "");
         tv_safe_number.setText(phone);
         // 重新进入设置向导textview点击侦听
         TextView tv_reset_setting = (TextView) findViewById(R.id.tv_reset_setting);
             tv_reset_setting.setOnClickListener(new OnClickListener()
             {

                 @Override
                 public void onClick(View v)
                 {
                     // 手机安全导航设置没有完成跳转到导航设置1的界面
                     Intent intent = new Intent(getApplicationContext(),
                             Setup1Activity.class);
                     startActivity(intent);
                     // 跳转到一个新的界面时需要关闭当前界面
                     finish();
                 }
             });
     }
 }

分析：由于调用initUI(),方法之前没有加载布局文件setContentView(R.layout.activity_setup_over);

导致后面45行tv_safe_number和48行tv_reset_setting通过findviewbyid方法调用时报出空指针

解决方案1：在protected void onCreate(Bundle savedInstanceState)方法体中添加setContentView(R.layout.activity_setup_over)，

解决方案2：在45行tv_safe_number和48行tv_reset_setting用到这两个指针是做if（tv_safe_number！=null）判断