写个android拨号器，运行是报如下错误
04-09 01:36:33.880: E/AndroidRuntime(3689): Caused by: java.lang.NullPointerException
04-09 01:36:33.880: E/AndroidRuntime(3689): at com.example.phone.MainActivity.onCreate(MainActivity.java:30)
网上找了很久也没有找到答案，请高手指点下
代码如下：
1 package com.example.phone;
23 import android.support.v7.app.ActionBarActivity;
4 import android.support.v7.app.ActionBar;
5 import android.support.v4.app.Fragment;
6 import android.text.TextUtils;
7 import android.content.Intent;
8 import android.net.Uri;
9 import android.os.Bundle;
10 import android.view.LayoutInflater;
11 import android.view.Menu;
12 import android.view.MenuItem;
13 import android.view.View;
14 import android.view.ViewGroup;
15 import android.view.View.OnClickListener;
16 import android.widget.Button;
17 import android.widget.EditText;
18 import android.widget.Toast;
19 import android.os.Build;
20
21 public class MainActivity extends ActionBarActivity {
22 public EditText call_number;
23
24 @Override
25 protected void onCreate(Bundle savedInstanceState) {
26 super.onCreate(savedInstanceState);
27 setContentView(R.layout.activity_main);
28 Button bt_call = (Button) findViewById(R.id.button);
29 call_number = (EditText) this.findViewById(R.id.et_number);
30 bt_call.setOnClickListener(new mybuttonclick());
31 if (savedInstanceState == null) {
32 getSupportFragmentManager().beginTransaction()
33 .add(R.id.container, new PlaceholderFragment()).commit();
34 }
35 }
36
37 private class mybuttonclick implements OnClickListener {
38
39 @Override
40 public void onClick(View v) {
41 String number = call_number.getText().toString().trim();
42 if (TextUtils.isEmpty(number)) {
43 Toast.makeText(MainActivity.this, "号码不能为空", Toast.LENGTH_SHORT)
44 .show();
45 return;
46 }
47 Intent intent = new Intent();
48 intent.setAction(Intent.ACTION_CALL);
49 intent.setData(Uri.parse("tel:" + number));
50 startActivity(intent);
51 }
52
53 }
54
55 /**
56 * A placeholder fragment containing a simple view.
57 */
58 public static class PlaceholderFragment extends Fragment {
59
60 public PlaceholderFragment() {
61 }
62
63 @Override
64 public View onCreateView(LayoutInflater inflater, ViewGroup container,
65 Bundle savedInstanceState) {
66 View rootView = inflater.inflate(R.layout.fragment_main, container,
67 false);
68 return rootView;
69 }
70 }
71
72 }
运行时报如下错误，求助
04-09 01:36:33.880: W/dalvikvm(3689): threadid=1: thread exiting with uncaught exception (group=0x40bcc300)
04-09 01:36:33.880: E/AndroidRuntime(3689): FATAL EXCEPTION: main
04-09 01:36:33.880: E/AndroidRuntime(3689): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.phone/com.example.phone.MainActivity}: java.lang.NullPointerException
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.app.ActivityThread.access$700(ActivityThread.java:131)
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1228)
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.os.Handler.dispatchMessage(Handler.java:99)
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.os.Looper.loop(Looper.java:137)
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.app.ActivityThread.main(ActivityThread.java:4866)
04-09 01:36:33.880: E/AndroidRuntime(3689): at java.lang.reflect.Method.invokeNative(Native Method)
04-09 01:36:33.880: E/AndroidRuntime(3689): at java.lang.reflect.Method.invoke(Method.java:511)
04-09 01:36:33.880: E/AndroidRuntime(3689): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-09 01:36:33.880: E/AndroidRuntime(3689): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-09 01:36:33.880: E/AndroidRuntime(3689): at dalvik.system.NativeStart.main(Native Method)
04-09 01:36:33.880: E/AndroidRuntime(3689): Caused by: java.lang.NullPointerException
04-09 01:36:33.880: E/AndroidRuntime(3689): at com.example.phone.MainActivity.onCreate(MainActivity.java:30)
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.app.Activity.performCreate(Activity.java:5143)
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
04-09 01:36:33.880: E/AndroidRuntime(3689): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
04-09 01:36:33.880: E/AndroidRuntime(3689): ... 11 more
java.lang.NullPointerException at com.example.phone.MainActivity.onCreate,布布扣,bubuko.com
java.lang.NullPointerException at com.example.phone.MainActivity.onCreate