我正在创建这个有三个标签的应用程序。 Tab1用于处理蓝牙传入和传出连接。这里出现的主要问题是，一旦我点击连接按钮就会创建连接但是当我切换标签然后跳回到tab1时，一切都会丢失，因为标签已重新初始化。我想阻止这种情况发生。请在我的代码中建议我更正。
这是MainActivity.java文件
public class MainActivity extends AppCompatActivity implements TabLayout.OnTabSelectedListener{
private TabLayout tabLayout;
StringBuilder recDataString = new StringBuilder();
int handlerState = 0;
private ViewPager viewPager;
int initialize = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
//Initializing the tablayout
tabLayout = (TabLayout)findViewById(R.id.tabLayout);
tabLayout.addTab(tabLayout.newTab().setText("Manual"));
tabLayout.setSelectedTabIndicatorColor(Color.BLACK);
tabLayout.addTab(tabLayout.newTab().setText("Status"));
tabLayout.addTab(tabLayout.newTab().setText("Database"));
tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);
viewPager = (ViewPager)findViewById(R.id.pager);
Pager adapter = new Pager(getSupportFragmentManager(),tabLayout.getTabCount());
viewPager.setAdapter(adapter);
tabLayout.setOnTabSelectedListener(this);
BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String id = intent.getStringExtra("BS");
Log.d("********", "ID = " + id);
/*if (id.equalsIgnoreCase("F")) {
sendToConnectedThread(id);
}*/
}
};
IntentFilter filter = new IntentFilter();
filter.addAction("com.example.nitesh.finaltab.DATA_BROADCAST");
getApplicationContext().registerReceiver(broadcastReceiver,filter);
}
public int getInitialize(){
return initialize;
}
public void setInitialize(int m){
this.initialize = m;
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
}
这是Pager.java文件
public class Pager extends FragmentStatePagerAdapter {
int tabcount;
public Pager(FragmentManager fm, int tabcount){
super(fm);
this.tabcount = tabcount;
}
@Override
public Fragment getItem(int position){
switch (position){
case 0:
Tab1 tab1 = new Tab1();
return tab1;
case 1:
Tab2 tab2 = new Tab2();
return tab2;
case 2:
Tab3 tab3 = new Tab3();
return tab3;
default:
return null;
}
}
@Override
public int getCount(){return tabcount;}
}
这是Tab1.java文件
public class Tab1 extends Fragment {
SQLiteDatabase alexadb,activitydb;
MainActivity mainActivity= new MainActivity();
StringBuilder recDataString = new StringBuilder();
String address = "98:D3:32:20:5A:57";
static final UUID myUUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
int handlerState = 0;
public boolean isBtConnected = false;
ProgressDialog progressDialog;
int initialize = 0;
Handler bluetoothIn;
BluetoothAdapter myBluetooth;
BluetoothSocket bluetoothSocket;
ConnectedThread connectedThread ;
Button connect,forward,reverse,left,right,stop;
int speed;
String datatoSend;
private final long REPEAT_DELAY = 50;
boolean autoIncreament,autoDecreament;
View view;
private Handler repeatUpdateHandler = new Handler();
private Handler senddataUpdatehandler = new Handler();
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
createDatabase();
view = inflater.inflate(R.layout.tab1, container, false);
forward = (Button) view.findViewById(R.id.bforward);
reverse = (Button) view.findViewById(R.id.breverse);
left = (Button) view.findViewById(R.id.bleft);
stop = (Button) view.findViewById(R.id.bstop);
connect = (Button)view.findViewById(R.id.buttonConnect);
right = (Button) view.findViewById(R.id.bright);
Toast.makeText(getContext(), "Tab1 Initiated", Toast.LENGTH_SHORT).show();
final AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(getContext());
alertDialogBuilder.setMessage("Ready to connect?");
handler();
class RepetitiveUpdater implements Runnable {
@Override
public void run() {
if (autoIncreament) {
increment();
repeatUpdateHandler.postDelayed(new RepetitiveUpdater(), REPEAT_DELAY);
} else if (autoDecreament) {
decrement();
repeatUpdateHandler.postDelayed(new RepetitiveUpdater(), REPEAT_DELAY);
}
}
}
connect.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
alertDialogBuilder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
Toast.makeText(getContext(), "Process Initiated", Toast.LENGTH_SHORT).show();
new CheckBT().execute();
}
});
alertDialogBuilder.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
}
});
AlertDialog alertDialog = alertDialogBuilder.create();
alertDialog.show();
}
});
right.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// bluetoothConnect.sendData("R");
Log.d("Right", "Button is clicked");
sendData("R");
insertIntoActivityDB("Right Button is clicked");
}
});
left.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
sendData("L");
insertIntoActivityDB("Left Button is clicked");
}
});
reverse.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
sendData("B");
insertIntoActivityDB("Reverse Button is clicked");
}
});
stop.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
autoDecreament = false;
autoIncreament = false;
sendData("S");
insertIntoActivityDB("Stop Button is clicked");
}
});
forward.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
increment();
sendData("F");
insertIntoActivityDB("Forward Button is clicked");
}
});
forward.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
autoIncreament = true;
autoDecreament = false;
repeatUpdateHandler.post(new RepetitiveUpdater());
return false;
}
});
forward.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_UP && autoIncreament) {
autoIncreament = false;
autoDecreament = true;
sendData("D");
repeatUpdateHandler.post(new RepetitiveUpdater());
}
return false;
}
});
return view;
}
public void handler() {
bluetoothIn = new Handler() {
public void handleMessage(android.os.Message msg) {
if (msg.what == handlerState) {
String readMessage = (String) msg.obj;
recDataString.append(readMessage);
int endofLineIndex = recDataString.indexOf("~");
if (endofLineIndex > 0) {
// String dataInPrint = recDataString.substring(0,endofLineIndex);
String data = recDataString.substring(1, endofLineIndex);
Log.d("Received Text", "" + data);
String first = recDataString.substring(0, 1);
Log.d("First letter ", "Hello" + first);
if (first.equalsIgnoreCase("P")) {
insertIntoAlexaDB(data);
}
if (first.equalsIgnoreCase("V")) {
insertIntoAlexaDB(data);
} else {
}
recDataString.delete(0, recDataString.length());
// dataInPrint = " ";
data = "";
first = " ";
}
}
}
};
}
public void increment(){
speed++;
sendData("F");
Log.d("Increasing Speed"," "+speed);
}
public void decrement() {
if (speed > 0) {
speed--;
sendData("D");
Log.d("Decreasing Speed", " " + speed);
}
}
public class CheckBT extends AsyncTask<Void, Void, Void>//UI Thread
{
private boolean ConnectSuccess = true;
@Override
protected void onPreExecute() {
progressDialog = ProgressDialog.show(getContext(), "Connecting you", "From Alexa");
Toast.makeText(getContext(),"Conneting",Toast.LENGTH_SHORT).show();
}
@Override
protected Void doInBackground(Void... params) {
try {
if (bluetoothSocket == null || !isBtConnected) {
myBluetooth = BluetoothAdapter.getDefaultAdapter();
BluetoothDevice device = myBluetooth.getRemoteDevice(address);
bluetoothSocket = device.createInsecureRfcommSocketToServiceRecord(myUUID); //Create RFCOMM connection
BluetoothAdapter.getDefaultAdapter().cancelDiscovery();
bluetoothSocket.connect();
}
} catch (IOException e) {
ConnectSuccess = false;
Toast.makeText(getContext(), "HC-05 didn't respond", Toast.LENGTH_SHORT).show();
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
if (!ConnectSuccess) {
Toast.makeText(getContext(), "Connection Failed. Try Again", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(getContext(), "Connected", Toast.LENGTH_SHORT).show();
isBtConnected = true;
connectedThread = new ConnectedThread(bluetoothSocket);
connectedThread.start();
}
progressDialog.dismiss();
}
}
private class ConnectedThread extends Thread{
private final InputStream mmInStream;
private final OutputStream mmOutStream;
//creation of the thread
public ConnectedThread(BluetoothSocket bluetoothSocket){
InputStream tmpIn = null;
OutputStream tmpOut = null;
try{
//create I/O streams for connection
tmpIn = bluetoothSocket.getInputStream();
tmpOut = bluetoothSocket.getOutputStream();
}catch (IOException
e){}
mmInStream = tmpIn;
mmOutStream = tmpOut;
}
public boolean getBluetoothStatus() {
Toast.makeText(getContext(),"Bluetooth Status from thread"+isBtConnected,Toast.LENGTH_SHORT).show();
return isBtConnected;
}
public void run(){
byte[] buffer = new byte[256];
int bytes;
//keep looping ot listen for received messages
while(true){
try{
Log.d("Running"," Connected_Thread");
isBtConnected = true;
bytes = mmInStream.read(buffer); //read bytes from input buffer
String readMessage = new String(buffer,0,bytes);
//Send the obtained bytes to the UIActivity via handler
bluetoothIn.obtainMessage(handlerState,bytes,-1,readMessage).sendToTarget();
}catch (IOException e){
break;
}
}
}
}
public void sendData(String data) {
try {
bluetoothSocket.getOutputStream().write(data.toString().getBytes());
} catch (IOException e) {
e.printStackTrace();
}
}
/**Creation of DATABASE**/
public void createDatabase(){
alexadb = getContext().openOrCreateDatabase("AlexaDB", Context.MODE_PRIVATE,null);
activitydb= getContext().openOrCreateDatabase("ActivityDB",Context.MODE_PRIVATE,null);
alexadb.execSQL("CREATE TABLE IF NOT EXISTS alexa(id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,data VARCHAR);");
activitydb.execSQL("CREATE TABLE IF NOT EXISTS activity(id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,data VARCHAR);");
}
public boolean insertIntoAlexaDB( String data){
if (data.equalsIgnoreCase(" ")) {
return false;
} else {
String query = "INSERT INTO alexa(data)VALUES('" + data + "');";
alexadb.execSQL(query);
return true;
}
}
public boolean insertIntoActivityDB(String data){
if (data.equalsIgnoreCase(" ")) {
return false;
} else {
String query = "INSERT INTO activity(data)VALUES('" + data + "');";
activitydb.execSQL(query);
return true;
}
}
}
答案 0 :(得分：0)
仅当您选择最后一个标签时才会发生这种情况吗？看一下offscreen page limit parameter：基本上你可以设置滚动ViewPager时要保留在内存中的页数。在您的情况下，屏幕外页面限制为2应足以始终将所有页面保留在内存中。