Question

我正在制作Android蓝牙应用程序，它可以打开或关闭蓝牙搜索设备配对设备等所有工作正常但是当我点击listview项目异常发生时连接设备上出现问题：

显示java.lang.NullPointerException

如何克服这种情况？

XML

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity" >

  <TextView
       android:id="@+id/text"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:textAppearance="?android:attr/textAppearanceLarge"
       android:text="@string/Text" />

   <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:orientation="horizontal"
      android:layout_marginTop="30dp" >

   <Button
      android:id="@+id/turnOn"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/on" />

   <Button
      android:id="@+id/turnOff"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/off" />

   </LinearLayout>


   <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:orientation="vertical"
      android:layout_marginTop="80dp" >

       <Button
          android:id="@+id/paired"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="@string/List" />

       <Button
          android:id="@+id/search"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="@string/Find" />

       <ListView
           android:id="@+id/listView1"
           android:layout_width="fill_parent"
           android:layout_height="200dp" >

       </ListView>

   </LinearLayout>

</RelativeLayout>

JavaCode

public ConnectThread(BluetoothDevice device) {
        BluetoothSocket tmp = null;
        mmDevice = device;
        try {
            tmp = device.createRfcommSocketToServiceRecord(MY_UUID);//Exception
        } catch (IOException e) { }
        mmSocket = tmp;
    }

logcat的

04-19 20:45:53.353  10902-10902/com.example.app W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x400205a0)
04-19 20:45:53.363  10902-10902/com.example.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
            at com.example.app.ConnectThread.<init>(ConnectThread.java:23)
            at com.example.app.MainActivity.connect(MainActivity.java:124)
            at com.example.app.MainActivity.access$000(MainActivity.java:30)
            at com.example.app.MainActivity$5.onItemClick(MainActivity.java:117)
            at android.widget.AdapterView.performItemClick(AdapterView.java:284)
            at android.widget.ListView.performItemClick(ListView.java:3561)
            at android.widget.AbsListView$PerformClick.run(AbsListView.java:1812)
            at android.os.Handler.handleCallback(Handler.java:587)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:143)
            at android.app.ActivityThread.main(ActivityThread.java:4277)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:507)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
            at dalvik.system.NativeStart.main(Native Method)
04-19 20:45:53.373      125-254/? W/ActivityManager﹕ Force finishing activity com.example.app/.MainActivity
04-19 20:45:53.873      125-140/? W/ActivityManager﹕ Activity pause timeout for HistoryRecord{407b6608 com.example.app/.MainActivity}
04-19 20:45:53.933      234-234/? I/CarouselTimeLog﹕ onStart() finish: 1429458353942

我正在制作蓝牙应用程序，一切顺利，直到我点击ListView，tmp = device.createRfcommSocketToServiceRecord(MY_UUID);处有例外

Answer 1

让我们看一下错误：

java.lang.NullPointerException
            at com.example.app.ConnectThread.<init>(ConnectThread.java:23)

问题出在这里：

public ConnectThread(BluetoothDevice device) {
    BluetoothSocket tmp = null;
    mmDevice = device;
    try {
        tmp = device.createRfcommSocketToServiceRecord(MY_UUID);//Exception
    } catch (IOException e) { }
    mmSocket = tmp;
}

在try语句中的行上：

tmp = device.createRfcommSocketToServiceRecord(MY_UUID);

这意味着device必须为null。这意味着您将空值传递给ConnectThread的构造函数。问题出在您创建BluetoothDevice对象的位置。

在Android中使用套接字连接蓝牙时出现异常

1 个答案: