inputStream.read（）導致NullPointerException（在檢查inputStream之后！= null）

Question

我正在編寫一個需要與藍牙2.1設備交換數據的應用程序。 我已經做了好幾次了，但這次發生了一些奇怪的事情。

    Log.d("TAG", "connectToDevice");

    if(macAddress != null)
        deviceToConnect = mBluetoothAdapter.getRemoteDevice(macAddress);

    Log.d("TAG", "macAddress != null");


    if(deviceToConnect != null)
        try {
            btSocket = deviceToConnect.createRfcommSocketToServiceRecord(UUID.fromString(SharedIncludes.SPP_UUID));
        } catch (IOException e) {
            btSocket = null;
            e.printStackTrace();
        }

    Log.d("TAG", "deviceToConnect != null");

    if(btSocket != null){

        try {
            inputStream = btSocket.getInputStream();
            Log.d("TAG", "inputStream OK");

        } catch (IOException e) {
            inputStream = null;
            Log.d("TAG", "inputStream KO");
            e.printStackTrace();
        }

        try {
            outputStream =  btSocket.getOutputStream();
            Log.d("TAG", "outputStream OK");

        } catch (IOException e) {
            outputStream = null;
            Log.d("TAG", "outputStream KO");
            e.printStackTrace();
        }

    }


    Log.d("TAG", "btSocket != null");
    Log.d("TAG", "onConnectionEstablished");

在發現階段之后，我得到了我需要連接的藍牙設備，然后我獲得了套接字，輸入和輸出流。

然后我有一個從輸入流中讀取的線程。

   int byteRead;

    while (listening) {
        try {
            if(inputStream!=null){
                Log.d("TAG", "inputStream: " +inputStream);
                byteRead = inputStream.read();
            }else{
                Log.d("TAG", "inputStream is null!");
                continue;
            } // Rest of the code here

我在執行inputStream.read()行時遇到此錯誤：

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.io.InputStream.read(byte[], int, int)' on a null object reference

at android.bluetooth.BluetoothSocket.read(BluetoothSocket.java:427)
at android.bluetooth.BluetoothInputStream.read(BluetoothInputStream.java:60)
at com.me.testapplication.Connection_BT21.run(Connection_BT21.java:152)

問題1：為什么NullPointerException如果我檢查inputStream！= null？

問題2：為什么讀取（byte []，int，int）如果我試圖調用read（）？

Answer 1

我發現了錯誤，你沒事：插座出錯了......我需要調用socket.connect（）！

if(macAddress != null)
    deviceToConnect = mBluetoothAdapter.getRemoteDevice(macAddress);

Log.d("TAG", "macAddress != null");


if(deviceToConnect != null)
    try {
        btSocket = deviceToConnect.createRfcommSocketToServiceRecord(UUID.fromString(SharedIncludes.SPP_UUID));
    } catch (IOException e) {
        btSocket = null;
        e.printStackTrace();
    }

Log.d("TAG", "deviceToConnect != null");

if(btSocket != null){
 //This was the line missing!
 btSocket.connect();

    try {
        inputStream = btSocket.getInputStream();
        Log.d("TAG", "inputStream OK");

    } catch (IOException e) {
        inputStream = null;
        Log.d("TAG", "inputStream KO");
        e.printStackTrace();
    }

    try {
        outputStream =  btSocket.getOutputStream();
        Log.d("TAG", "outputStream OK");

    } catch (IOException e) {
        outputStream = null;
        Log.d("TAG", "outputStream KO");
        e.printStackTrace();
    }

}

這就是為什么inputStream沒有准備好，我得到了那個錯誤。

對不起，我只是沒有看到它..希望它可以幫助別人！

Answer 2

問題1：為什么NullPointerException如果我檢查inputStream！= null？

你得到一個NullPointerException，而不是因為你的inputStream是null，你的InputStream很好; 但是在BluetoothSocket.java或BluetoothInputStream.java有一個InputStream，它是null，並且正在調用read方法。

問題2：為什么讀取（byte []，int，int）如果我試圖調用read（）？

涉及問題一。 int java.io.InputStream.read(byte[], int, int)在其他一個文件中調用，在null InputStream上。