Question

当我尝试实现从一个活动向扩展服务的BluetoothService Activity发送字符串消息的代码时，为什么会出现NullPointerException错误。

以下是发送字符串所涉及的代码的主要部分：

private BluetoothService mChatService = null;

public void onCaptureButtonClicked(View view) throws IOException{                                   
            try{
                    sendMessage("1");
                }catch(NullPointerException e){
                    e.printStackTrace();
                }

            takePhoto(1);
        }
        }

private void sendMessage(String message) {

             if (mChatService.getState() != BluetoothService.STATE_CONNECTED) {
             return;
         }

         if (message.length() > 0) {
             byte[] send = message.getBytes();
             mChatService.write(send);
         }
     }

这是错误logcat：

02-15 18:21:19.960: W/System.err(1252): java.lang.NullPointerException
02-15 18:21:19.960: W/System.err(1252):     at com.example.application.parss.CameraActivity.sendMessage(CameraActivity.java:751)
02-15 18:21:19.960: W/System.err(1252):     at com.example.application.parss.CameraActivity.onCaptureButtonClicked(CameraActivity.java:245)
02-15 18:21:19.960: W/System.err(1252):     at java.lang.reflect.Method.invokeNative(Native Method)
02-15 18:21:19.960: W/System.err(1252):     at java.lang.reflect.Method.invoke(Method.java:507)
02-15 18:21:19.960: W/System.err(1252):     at android.view.View$1.onClick(View.java:2180)
02-15 18:21:19.960: W/System.err(1252):     at android.view.View.performClick(View.java:2585)
02-15 18:21:19.960: W/System.err(1252):     at android.view.View$PerformClick.run(View.java:9299)
02-15 18:21:19.960: W/System.err(1252):     at android.os.Handler.handleCallback(Handler.java:587)
02-15 18:21:19.960: W/System.err(1252):     at android.os.Handler.dispatchMessage(Handler.java:92)
02-15 18:21:19.960: W/System.err(1252):     at android.os.Looper.loop(Looper.java:130)
02-15 18:21:19.960: W/System.err(1252):     at android.app.ActivityThread.main(ActivityThread.java:3691)
02-15 18:21:19.960: W/System.err(1252):     at java.lang.reflect.Method.invokeNative(Native Method)
02-15 18:21:19.970: W/System.err(1252):     at java.lang.reflect.Method.invoke(Method.java:507)
02-15 18:21:19.970: W/System.err(1252):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:912)
02-15 18:21:19.970: W/System.err(1252):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:670)
02-15 18:21:19.970: W/System.err(1252):     at dalvik.system.NativeStart.main(Native Method)

编辑：

我以这种方式推介了mChatSession：

 mChatService = new BluetoothService(this, mHandler);

并称之为： mChatService.write（发送）;

但类似的NullPointerException错误仍然存在。

Answer 1

我猜你得到了例外，因为你还没有初始化BluetoothService。

private BluetoothService mChatService = null;

您在mChatService.getState()方法中使用sendMessage()而未初始化。

Answer 2

尝试

     if(mChatService == null)
         return;
     if (message.length() > 0 && mChatService.getState() == BluetoothService.STATE_CONNECTED) {
         byte[] send = message.getBytes();
         mChatService.write(send);
     }

Answer 3

BluetoothService mChatService = new BluetoothService(args);

您需要在某个时刻为变量分配一个实例。

尝试将消息从一个活动发送到另一个活动时出现空指针异常

3 个答案: