NullPointerExceptionnull 指標異常——沒有事先載入布局檔案到acitivy——缺少：setContentView(R.layout.activity_setup_over);，

NullPointerExceptionnull 指標異常——沒有事先載入布局檔案到acitivy——缺少：setContentView(R.layout.activity_setup_over);，

null 指標異常：

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)

相應代碼：

 1 package com.itheima.mobilesafe74.activity; 2  3 import com.itheima.mobilesafe74.R; 4 import com.itheima.mobilesafe74.utils.ConstentValue; 5 import com.itheima.mobilesafe74.utils.SpUtil; 6 import android.app.Activity; 7 import android.content.Intent; 8 import android.os.Bundle; 9 import android.view.View;10 import android.view.View.OnClickListener;11 import android.widget.TextView;12 13 /**14  * 說明 :手機安全導航設定完成的介面15  */16 public class SetupOverActivity extends Activity17 {18     @Override19     protected void onCreate(Bundle savedInstanceState)20     {21         super.onCreate(savedInstanceState);22 //        setContentView(R.layout.activity_setup_over);23         boolean setup_over = SpUtil.getBoolean(this, ConstentValue.SETUP_OVER,24                 false);25         if (setup_over)26         {27             // 手機安全導航設定完成跳轉到設定完成的介面28             setContentView(R.layout.activity_setup_over);29         } else30         {31             // 手機安全導航設定沒有完成跳轉到導航設定1的介面32             Intent intent = new Intent(this, Setup1Activity.class);33             startActivity(intent);34             // 跳轉到一個新的介面時需要關閉當前介面35             finish();36         }37         initUI();38     }39 40     private void initUI()41     {42 43         TextView tv_safe_number = (TextView) findViewById(R.id.tv_safe_number);44         String phone = SpUtil.getString(this, ConstentValue.CONTACT_PHONE, "");45         tv_safe_number.setText(phone);46         // 重新進入設定嚮導textview點擊偵聽47         TextView tv_reset_setting = (TextView) findViewById(R.id.tv_reset_setting);48             tv_reset_setting.setOnClickListener(new OnClickListener()49             {50 51                 @Override52                 public void onClick(View v)53                 {54                     // 手機安全導航設定沒有完成跳轉到導航設定1的介面55                     Intent intent = new Intent(getApplicationContext(),56                             Setup1Activity.class);57                     startActivity(intent);58                     // 跳轉到一個新的介面時需要關閉當前介面59                     finish();60                 }61             });62     }63 }

View Code

分析：由於調用initUI(),方法之前沒有載入布局檔案setContentView(R.layout.activity_setup_over);

導致後面45行tv_safe_number和48行tv_reset_setting通過findviewbyid方法調用時報出null 指標

解決方案1：在protected void onCreate(Bundle savedInstanceState)方法體中添加setContentView(R.layout.activity_setup_over)，

解決方案2：在45行tv_safe_number和48行tv_reset_setting用到這兩個指標是做if（tv_safe_number！=null）判斷