Android Bluetooth App Wont Run Due To Null Pointer Error

Bluetooth app won't run due to Null pointer exceptions. No errors, but I can't see to connect to the emulator as the app just crashes every time. Even if I try sample GitHub codes,

Solution 1:

It looks like the problem is from line 59: if (!mBluetoothAdapter.isEnabled()) {

Note: The error message says line 57, but in my text editor it says 59.

A few lines above, you check whether the object mBluetoothAdapter was successfully created by checking if it's == null. But after that, you call its method: .isEnabled(). I think the problem is that mBluetoothAdapter is becoming null and therefore throws a NullPointerException when you try to access one of its methods.

If I understand correctly, I think the solution would be something like this:

// check if bluetooth is availableif(mBluetoothAdapter == null){
    mBluetoothStatus.setText("Bluetooth is not available");
}
else {
    mBluetoothStatus.setText("Bluetooth is available");
    //if Bluetooth isnt enabled, enable itif (!mBluetoothAdapter.isEnabled()) {
        IntentenableBtIntent=newIntent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
    }
}

This would keep the enabling code away from a mBluetoothAdapter with a value of null.

Alternativly, you could use return to exit the method if BlueTooth isn't available.

// check if bluetooth is availableif(mBluetoothAdapter == null){
    mBluetoothStatus.setText("Bluetooth is not available");
    return;
}
else {
    mBluetoothStatus.setText("Bluetooth is available");
    }
    //if Bluetooth isnt enabled, enable itif (!mBluetoothAdapter.isEnabled()) {
   IntentenableBtIntent=newIntent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
   startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}

This would do the same in a little bit of a cleaner way.

I think the next step for you is to find out why BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter(); is returning null instead of the object you want. I don't think the answer to that is in your MainActivity method. The device isn't finding a default adapter and that could be the result of numerous problems.