线程退出与未捕获的异常（组= 0x41a03700）

Question

使用未捕获的异常获取线程退出（group = 0x41a03700） 我想查看连接的usb设备列表，但我的应用程序崩溃请告诉我我错误的地方

这是我的代码：

package com.example.demo2c1testpanel;

import java.nio.ByteBuffer;
import java.util.HashMap;
import java.util.Iterator;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.hardware.usb.UsbConstants;
import android.hardware.usb.UsbDevice;
import android.hardware.usb.UsbDeviceConnection;
import android.hardware.usb.UsbEndpoint;
import android.hardware.usb.UsbInterface;
import android.hardware.usb.UsbManager;
import android.hardware.usb.UsbRequest;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class Loginpage extends Activity
{
    public static final int targetVendorID = 6790;      
    public static final int targetProductID = 29987;
    HashMap<String, UsbDevice> devicelist= null;


    public  UsbManager manager;
    public  UsbDeviceConnection usbDeviceConnection;
    public  UsbInterface usbInterfaceFound = null;
    public  UsbEndpoint endpointOut = null;
    public  UsbEndpoint endpointIn = null;
    public  UsbDevice usbdevice;




    Button clear,signin;
    EditText username,password;
    String i = "";
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.loginpage);

        signin = (Button)findViewById(R.id.btn_signin);
        signin.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {

                check_connection();


            }       
            });

            }

    public void check_connection() 
    {

    manager = (UsbManager)getSystemService(Context.USB_SERVICE);
    devicelist = manager.getDeviceList();
    if(devicelist!=null)
    {
        if(usbdevice.getProductId()==targetProductID && usbdevice.getVendorId()==targetVendorID)
        {
            Toast.makeText(Loginpage.this, "Device connected", Toast.LENGTH_LONG).show();
        }
    }
    else

        Toast.makeText(Loginpage.this, "No Device connected", Toast.LENGTH_LONG).show();





}
}

这是我的logcat：

01-02 02:23:55.990: W/dalvikvm(8163): threadid=1: thread exiting with uncaught exception (group=0x41a03700)
01-02 02:23:56.000: E/AndroidRuntime(8163): FATAL EXCEPTION: main
01-02 02:23:56.000: E/AndroidRuntime(8163): java.lang.NullPointerException
01-02 02:23:56.000: E/AndroidRuntime(8163):     at com.example.demo2c1testpanel.Loginpage.check_connection(Loginpage.java:72)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at com.example.demo2c1testpanel.Loginpage$1.onClick(Loginpage.java:57)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at android.view.View.performClick(View.java:4240)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at android.view.View$PerformClick.run(View.java:17721)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at android.os.Handler.handleCallback(Handler.java:730)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at android.os.Handler.dispatchMessage(Handler.java:92)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at android.os.Looper.loop(Looper.java:137)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at android.app.ActivityThread.main(ActivityThread.java:5103)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at java.lang.reflect.Method.invokeNative(Native Method)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at java.lang.reflect.Method.invoke(Method.java:525)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-02 02:23:56.000: E/AndroidRuntime(8163):     at dalvik.system.NativeStart.main(Native Method)

我的宣言：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.demo2c1testpanel"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".Homescreen"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Loginpage"
            android:label="@string/title_activity_loginpage" >
        </activity>

        <intent-filter>
            <action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
        </intent-filter>

        <meta-data
            android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"
            android:resource="@xml/device_filter" />
        <activity
            android:name=".Testspage"
            android:label="@string/title_activity_testpage" >
        </activity>
    </application>

</manifest>

这是我在onClickListener之后的工作代码：

public void check_connection() 
    {

        int i,j;
        String as[];
        UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
        HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
        i = deviceList.size();
        if(i==0)
        {
            Toast.makeText(Loginpage.this,"Device Not Connected",Toast.LENGTH_LONG).show();
            return;
        }
        as = new String[i];
        deviceList.keySet().toArray(as);
        for(j=0;j<i;j++)
        {
            device_details = (UsbDevice)deviceList.get(as[j]);
            if((device_details.getVendorId()==targetVendorID) && (device_details.getProductId()==targetProductID))
            {

                    Toast.makeText(Loginpage.this,"Device Connected",Toast.LENGTH_LONG).show();

            }
        }
}