空指针异常

[q5661889]

这是短信接收类：

package com.example.bluetooth___watch;



import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.telephony.SmsMessage;
import android.widget.Toast;

public class SMSReceiver extends BroadcastReceiver {
	/* 当收到短信时，就会触发此方法 */
	public void onReceive(Context context, Intent intent) {
		Bundle bundle = intent.getExtras();
		Object messages[] = (Object[]) bundle.get("pdus");
		SmsMessage smsMessage[] = new SmsMessage[messages.length];
		for (int n = 0; n < messages.length; n++) {
			smsMessage[n] = SmsMessage.createFromPdu((byte[]) messages[n]);
		}
		// 产生一个Toast
		Toast toast = Toast.makeText(context,
				"短信内容: " + smsMessage[0].getMessageBody(), Toast.LENGTH_LONG);
		// 设置toast显示的位置
		// toast.setGravity(Gravity.TOP|Gravity.LEFT, 0, 200);
		// 显示该Toast
		toast.show();

		  //调用显示短信内容的Activity
		 
		Intent in = new Intent();
		   in.setClass(context, MainActivity.class);
		   in.putExtra("message", smsMessage[0].getMessageBody());
		   context.startActivity(in);
	}
	
}

这是主类：

package com.example.bluetooth___watch;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.content.Intent;
import android.os.Bundle;
import android.view.Gravity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity {
	String username ;
	/* 取得默认的蓝牙适配器 */
	private BluetoothAdapter _bluetooth = BluetoothAdapter.getDefaultAdapter();

	/* 请求打开蓝牙 */
	private static final int REQUEST_ENABLE = 0x1;
	/* 请求能够被搜索 */
	private static final int REQUEST_DISCOVERABLE = 0x2;

	Button Button1, Button2, Button3,Button4;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);

		Button1 = (Button) findViewById(R.id.open_bluetooth);
		Button2 = (Button) findViewById(R.id.Can_be_searched);
		Button3 = (Button) findViewById(R.id.search_device);
		Button4 = (Button) findViewById(R.id.Show_Message);
		// 设置按钮1的事件监听
		Button1.setOnClickListener(new Button.OnClickListener() {
			public void onClick(View v) {
				// 用户请求打开蓝牙
				// Intent enabler = new
				// Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
				// startActivityForResult(enabler, REQUEST_ENABLE);
				// 打开蓝牙
				_bluetooth.enable();
			}
		});

		// 设置按钮2的事件监听
		Button2.setOnClickListener(new Button.OnClickListener() {
			/* 使设备能够被搜索 */
			public void onClick(View v)

			{

				Intent enabler = new Intent(
						BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
				startActivityForResult(enabler, REQUEST_DISCOVERABLE);
			}
		});

		// 设置按钮3的事件监听
		Button3.setOnClickListener(new Button.OnClickListener() {
			/* 开始搜索 */
			public void onClick(View v)

			{

				Intent enabler = new Intent(MainActivity.this,
						DiscoveryActivity.class);
				startActivity(enabler);
			}

		});
		
		  Bundle bu = this.getIntent().getExtras();
          username = bu.getString("message");//获取短信内容
		/*
		// 设置按钮4的事件信息 */
		Button4.setOnClickListener(new Button.OnClickListener() {
			
			public void onClick(View v)
			{
	
		
		 
				DisplayToast(username);
			}
		});

	}
	
	
	
/* 显示Toast */
public void DisplayToast(String str) {
	Toast.makeText(this, str, Toast.LENGTH_SHORT).show();
}
}

报错信息：
11-13 10:49:24.180: D/AndroidRuntime(11931): Shutting down VM
11-13 10:49:24.180: W/dalvikvm(11931): threadid=1: thread exiting with uncaught exception (group=0x420112b8)
11-13 10:49:24.180: E/AndroidRuntime(11931): FATAL EXCEPTION: main
11-13 10:49:24.180: E/AndroidRuntime(11931): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bluetooth___watch/com.example.bluetooth___watch.MainActivity}: java.lang.NullPointerException
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2118)
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2143)
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.app.ActivityThread.access$700(ActivityThread.java:140)
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.os.Handler.dispatchMessage(Handler.java:99)
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.os.Looper.loop(Looper.java:137)
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.app.ActivityThread.main(ActivityThread.java:4952)
11-13 10:49:24.180: E/AndroidRuntime(11931): at java.lang.reflect.Method.invokeNative(Native Method)
11-13 10:49:24.180: E/AndroidRuntime(11931): at java.lang.reflect.Method.invoke(Method.java:511)
11-13 10:49:24.180: E/AndroidRuntime(11931): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
11-13 10:49:24.180: E/AndroidRuntime(11931): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
11-13 10:49:24.180: E/AndroidRuntime(11931): at dalvik.system.NativeStart.main(Native Method)
11-13 10:49:24.180: E/AndroidRuntime(11931): Caused by: java.lang.NullPointerException
11-13 10:49:24.180: E/AndroidRuntime(11931): at com.example.bluetooth___watch.MainActivity.onCreate(MainActivity.java:61)
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.app.Activity.performCreate(Activity.java:5188)
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
11-13 10:49:24.180: E/AndroidRuntime(11931): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2082)
11-13 10:49:24.180: E/AndroidRuntime(11931): ... 11 more
11-13 10:54:30.160: I/Process(11931): Sending signal. PID: 11931 SIG: 9

[heaven_wsh]

11-13 10:49:24.180: E/AndroidRuntime(11931): Caused by: java.lang.NullPointerException 11-13 10:49:24.180: E/AndroidRuntime(11931): at com.example.bluetooth___watch.MainActivity.onCreate(MainActivity.java:61) 显示61行有空指针，你贴出来的代码和你出错时候的代码是一个版本吗

[answer艾]

你在有数据产生的地方 放logcat 显示出来 你看看你自己哪个数据没有应用到就知道了

[红袖满楼招]

11-13 10:49:24.180: E/AndroidRuntime(11931): at com.example.bluetooth___watch.MainActivity.onCreate(MainActivity.java:61)