android BluetoothChat use send receive methods fro

Hello im using the BluetoothChat example in order to communicate with an arduino. Everything works so far and now i want to access the sendMessage() method in order to be able to send data not from the main class but from another that ive created. Here is the BluetoothChat send function in the BluetoothChat.java

private void sendMessage(String message) {
    // Check that we're actually connected before trying anything
    if (mChatService.getState() != BluetoothChatService.STATE_CONNECTED) {
        Toast.makeText(this, R.string.not_connected, Toast.LENGTH_SHORT).show();
        return;
    }

    // Check that there's actually something to send
    if (message.length() > 0) {
        // Get the message bytes and tell the BluetoothChatService to write
        byte[] send = message.getBytes();
        mChatService.write(send);
        // Reset out string buffer to zero and clear the edit text field
        mOutStringBuffer.setLength(0);
        mOutEditText.setText(mOutStringBuffer);
    }
}

Now i want to access it from my Config.java . Here is what i have done so far. I changed the private void sendMessage to public and in the Config.java ive added these:

BluetoothChat firstClass = new BluetoothChat();

and in onCreate this

firstClass.sendMessage("test");

Although im not getting any errors when im switching to the Config.java activity the app crashes..
Can anyone help me with this? Thanx!

logcat

10-08 22:49:15.125: D/dalvikvm(1541): GC_EXTERNAL_ALLOC freed 98K, 47% free 2962K/5511K, external 3943K/4883K, paused 23ms 10-08 22:49:15.128: D/BluetoothSocket(1541): socket already in closing state:android.bluetooth.BluetoothSocket@40535c88 10-08 22:49:15.128: D/BluetoothSocket(1541): socket already in closing state:android.bluetooth.BluetoothSocket@40523b10 10-08 22:49:15.296: E/BluetoothChat(1541): -- ON STOP -- 10-08 22:49:20.585: D/AndroidRuntime(1541): Shutting down VM 10-08 22:49:20.585: W/dalvikvm(1541): threadid=1: thread exiting with uncaught exception (group=0x40015578) 10-08 22:49:20.589: E/AndroidRuntime(1541): FATAL EXCEPTION: main 10-08 22:49:20.589: E/AndroidRuntime(1541): java.lang.NullPointerException 10-08 22:49:20.589: E/AndroidRuntime(1541): at com.example.android.BluetoothChat.BluetoothChat.sendMessage(BluetoothChat.java:218) 10-08 22:49:20.589: E/AndroidRuntime(1541): at com.example.android.BluetoothChat.Config.onItemSelected(Config.java:45) 10-08 22:49:20.589: E/AndroidRuntime(1541): at android.widget.AdapterView.fireOnSelected(AdapterView.java:871) 10-08 22:49:20.589: E/AndroidRuntime(1541): at android.widget.AdapterView.access$200(AdapterView.java:42) 10-08 22:49:20.589: E/AndroidRuntime(1541): at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:837) 10-08 22:49:20.589: E/AndroidRuntime(1541): at android.os.Handler.handleCallback(Handler.java:587) 10-08 22:49:20.589: E/AndroidRuntime(1541): at android.os.Handler.dispatchMessage(Handler.java:92) 10-08 22:49:20.589: E/AndroidRuntime(1541): at android.os.Looper.loop(Looper.java:130) 10-08 22:49:20.589: E/AndroidRuntime(1541): at android.app.ActivityThread.main(ActivityThread.java:3687) 10-08 22:49:20.589: E/AndroidRuntime(1541): at java.lang.reflect.Method.invokeNative(Native Method) 10-08 22:49:20.589: E/AndroidRuntime(1541): at java.lang.reflect.Method.invoke(Method.java:507) 10-08 22:49:20.589: E/AndroidRuntime(1541): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842) 10-08 22:49:20.589: E/AndroidRuntime(1541): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600) 10-08 22:49:20.589: E/AndroidRuntime(1541): at dalvik.system.NativeStart.main(Native Method)

回答1:

BluetoothChat class is an activity. Activity objects are managed by Android OS (created, onCreate, onResume and other methods are called).

So, you shoudn't do something like this:

BluetoothChat firstClass = new BluetoothChat();

There are couple of ways how you can reuse this functionality

a) Copy from BluetoothChat and paste it to Config (let's for one second forget about code duplication).

You will need to copy the code from onCreate, onStart and other methods which manages mBluetoothAdaptor method

b) If you are going to keep both BluetoothChat activity and Config activity, you can move reusable code to some helper class (which isn't activity) and use it from both activities.

P.S. I would recommend to read up a little bit about activities, their lifecycle, because without this knowledge it will be very hard to develop any android app.

回答2:

You need Thread's or AsyncTask for send ant message from Android via Bluetooth. See this simple example: http://english.cxem.net/arduino/arduino5.php