尝试通过蓝牙发送数据时，Android蓝牙应用程序崩溃。我能够开机，发现并显示配对的设备。但是，当我尝试发送文件按钮时，它崩溃了。我在调试器中收到这些错误。
Process: com.example.bluetooth_demoproject, PID: 31320
java.lang.NullPointerException: Attempt to get length of null
array
at com.example.bluetooth_demoproject.MainActivity.ListDir(MainActivity.java:253)
at com.example.bluetooth_demoproject.MainActivity.onPrepareDialog(MainActivity.java:228)
at android.app.Activity.onPrepareDialog(Activity.java:4000)
at android.app.Activity.showDialog(Activity.java:4063)
at android.app.Activity.showDialog(Activity.java:4014)
at
com.example.bluetooth_demoproject.MainActivity$1.onClick(MainActivity.java:75)
at android.view.View.performClick(View.java:6896)
at
android.widget.TextView.performClick(TextView.java:12689)
at android.view.View$PerformClick.run(View.java:26088)
at android.os.Handler.handleCallback(Handler.java:789)
at android.os.Handler.dispatchMessage(Handler.java:98)
at android.os.Looper.loop(Looper.java:164)
at
android.app.ActivityThread.main(ActivityThread.java:6940)
at java.lang.reflect.Method.invoke(Native Method)
at
com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
这也是我的MainActivity。如果有更好的方法通过发送文件 蓝牙，请指出或帮助我的代码。
public class MainActivity extends Activity {
// Creating objects -----------------------------
private static final int REQUEST_ENABLE_BT = 0;
private static final int REQUEST_DISCOVER_BT_ = 1;
private static int CUSTOM_DIALOG_ID;
ListView dialog_ListView;
TextView mBluetoothStatus, mPairedDevicesList, mTextFolder;
ImageView mBluetoothIcon;
Button mOnButton, mOffButton, mDiscoverableButton, mPairedDevices,
mbuttonOpenDialog, msendBluetooth, mbuttonUp;
File root, fileroot, curFolder;
EditText dataPath;
private static final int DISCOVER_DURATION = 300;
private List<String> fileList = new ArrayList<String>();
// -------------------------------------------------------
BluetoothAdapter mBlueAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dataPath =(EditText) findViewById(R.id.FilePath);
mTextFolder = findViewById(R.id.folder);
mBluetoothStatus = findViewById(R.id.BluetoothStatus);
mBluetoothIcon = findViewById(R.id.bluetoothIcon);
mOnButton = findViewById(R.id.onButton);
mOffButton = findViewById(R.id.offButton);
mDiscoverableButton = findViewById(R.id.discoverableButton);
mPairedDevices = findViewById(R.id.pairedDevices);
mPairedDevicesList = findViewById(R.id.pairedDeviceList);
mbuttonOpenDialog = findViewById(R.id.opendailog);
msendBluetooth = findViewById(R.id.sendBluetooth);
mbuttonUp = findViewById(R.id.up);
mbuttonOpenDialog.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
dataPath.setText("");
showDialog(CUSTOM_DIALOG_ID);
}
});
root = new
File(Environment.getExternalStorageDirectory().getAbsolutePath());
curFolder = root;
msendBluetooth.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
sendViaBluetooth();
}
});
//adapter
mBlueAdapter = BluetoothAdapter.getDefaultAdapter();
if(mBlueAdapter == null){
mBluetoothStatus.setText("Bluetooth is not available");
return;
}
else {
mBluetoothStatus.setText("Bluetooth is available");
}
//if Bluetooth isnt enabled, enable it
if (!mBlueAdapter.isEnabled()) {
Intent enableBtIntent = new
Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}
//set image according to bluetooth Status
if (mBlueAdapter.isEnabled()) {
mBluetoothIcon.setImageResource(R.drawable.action_on);
}
else {
mBluetoothIcon.setImageResource(R.drawable.action_off);
}
//on button Click
mOnButton.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
if (!mBlueAdapter.isEnabled()) {
showToast("Turning Bluetooth on...");
// intent to on bluetooth
Intent intent = new
Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(intent, REQUEST_ENABLE_BT);
}
else {
showToast("Bluetooth is already on");
}
}
});
//discover Bluetooth button
mDiscoverableButton.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v){
if (!mBlueAdapter.isDiscovering()) {
showToast("Making device discoverable");
Intent intent = new
Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
startActivityForResult(intent, REQUEST_DISCOVER_BT_);
}
}
});
// off button click
mOffButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (mBlueAdapter.isEnabled()) {
showToast("Turning Bluetooth off...");
// intent to turn off bluetooth
mBluetoothIcon.setImageResource(R.drawable.action_off);
}
else{
showToast("Bluetooth is already off");
}
}
});
//get paired device button click
mPairedDevices.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (mBlueAdapter.isEnabled()) {
mPairedDevices.setText("Paired Devices");
Set<BluetoothDevice> devices =
mBlueAdapter.getBondedDevices();
for (BluetoothDevice device : devices){
mPairedDevices.append("\nDevice: " + device.getName() +
"," + device );
}
}
else {
//bluetooth is off and cant get paired devices
showToast("Turn on bluetooth to get paired devices");
}
}
});
}
@Override
protected Dialog onCreateDialog(int id) {
Dialog dialog = null;
if (id == CUSTOM_DIALOG_ID) {
dialog = new Dialog(MainActivity.this);
dialog.setContentView(R.layout.dailoglayout);
dialog.setTitle("File Selector");
dialog.setCancelable(true);
dialog.setCanceledOnTouchOutside(true);
mTextFolder = (TextView) dialog.findViewById(R.id.folder);
mbuttonUp = (Button) dialog.findViewById(R.id.up);
mbuttonUp.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
ListDir(curFolder.getParentFile());
}
});
dialog_ListView = (ListView) dialog.findViewById(R.id.dialoglist);
dialog_ListView.setOnItemClickListener(new
AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int
position, long id) {
File selected = new File(fileList.get(position));
if (selected.isDirectory()) {
ListDir(selected);
} else if (selected.isFile()) {
getSelectedFile(selected);
} else {
dismissDialog(CUSTOM_DIALOG_ID);
}
}
});
}
return dialog;
}
@Override
protected void onPrepareDialog(int id, Dialog dialog) {
super.onPrepareDialog(id, dialog);
if (id == CUSTOM_DIALOG_ID) {
ListDir(curFolder);
}
}
public void getSelectedFile(File f) {
dataPath.setText(f.getAbsolutePath());
fileList.clear();
dismissDialog(CUSTOM_DIALOG_ID);
}
public void ListDir(File f) {
if (f.equals(root)) {
mbuttonUp.setEnabled(false);
}
else {
mbuttonUp.setEnabled(true);
}
curFolder = f;
mTextFolder.setText(f.getAbsolutePath());
dataPath.setText(f.getAbsolutePath());
File[] files = f.listFiles();
fileList.clear();
for (File file : files) {
fileList.add(file.getPath());
}
ArrayAdapter<String> directoryList = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, fileList);
dialog_ListView.setAdapter(directoryList);
}
// exits to app --------------------------------
public void exit(View V) {
mBlueAdapter.disable();
Toast.makeText(this, "*** Now bluetooth is off...",
Toast.LENGTH_LONG).show();
finish();
}
// send file via bluetooth ------------------------
public void sendViaBluetooth() {
if(!dataPath.equals(null)) {
if(mBlueAdapter == null) {
Toast.makeText(this, "Device doesnt support bluetooth",
Toast.LENGTH_LONG).show();
}
else {
enableBluetooth();
}
}
else {
Toast.makeText(this, "please select a file",
Toast.LENGTH_LONG).show();
}
}
public void enableBluetooth() {
showToast("Making device discoverable");
Intent intent = new
Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
startActivityForResult(intent, REQUEST_DISCOVER_BT_);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent
data) {
if (resultCode == DISCOVER_DURATION && requestCode ==
REQUEST_DISCOVER_BT_) {
Intent i = new Intent();
i.setAction(Intent.ACTION_SEND);
i.setType("*/*");
File file = new File(dataPath.getText().toString());
i.putExtra(Intent.EXTRA_STREAM, Uri.fromFile(file));
PackageManager pm = getPackageManager();
List<ResolveInfo> list = pm.queryIntentActivities(i, 0);
if (list.size() > 0) {
String packageName = null;
String className = null;
boolean found = false;
for (ResolveInfo info : list) {
packageName = info.activityInfo.packageName;
if (packageName.equals("com.android.bluetooth")) {
className = info.activityInfo.name;
found = true;
}
}
//CHECK BLUETOOTH available or not------------------------------
------------------
if (!found) {
Toast.makeText(this, "Bluetooth not been found",
Toast.LENGTH_LONG).show();
} else {
i.setClassName(packageName, className);
startActivity(i);
}
}
} else {
Toast.makeText(this, "Bluetooth is cancelled",
Toast.LENGTH_LONG).show();
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
return super.onOptionsItemSelected(item);
}
//toast message function
private void showToast(String msg) {
Toast.makeText(this, msg, Toast.LENGTH_SHORT) .show();
}
}