我對 Android Studio 完全陌生，剛剛學習了面向物件的編程。我的專案要求我在開源代碼上構建一些東西。我在選單中添加了一個新選單項，并希望在用戶單擊具有 id:plot 的選單項后開始另一個活動。意圖將從 TerminalFragment 的 onOptionsItemSelected(MenuItem item) 內的 if (id == R.id.plot) 發送。為了使用選單構建 activity_main2，我按照互聯網上的食譜進行操作。我在測驗時發現activity_main2的頁面是空白的（全黑，沒有工具列或選單）。我的代碼缺少什么？
終端片段
package de.kai_morich.simple_bluetooth_le_terminal;
import android.app.Activity;
import android.app.AlertDialog;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.text.Editable;
import android.text.Spannable;
import android.text.SpannableStringBuilder;
import android.text.method.ScrollingMovementMethod;
import android.text.style.ForegroundColorSpan;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import android.widget.EditText;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
public class TerminalFragment extends Fragment implements ServiceConnection, SerialListener {
private MenuItem menuItem;
private enum Connected { False, Pending, True }
private String deviceAddress;
private SerialService service;
private TextView receiveText;
private TextView sendText;
private TextUtil.HexWatcher hexWatcher;
private Connected connected = Connected.False;
private boolean initialStart = true;
private boolean hexEnabled = false;
private boolean pendingNewline = false;
private String newline = TextUtil.newline_crlf;
/*
* Lifecycle
*/
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
//Register with activity
// You must inform the system that your app bar fragment is participating in the population of the options menu.
// tells the system that your fragment would like to receive menu-related callbacks.
setRetainInstance(true);
deviceAddress = getArguments().getString("device");
}
@Override
public void onDestroy() {
if (connected != Connected.False)
disconnect();
getActivity().stopService(new Intent(getActivity(), SerialService.class));
super.onDestroy();
}
@Override
public void onStart() {
super.onStart();
if(service != null)
service.attach(this);
else
getActivity().startService(new Intent(getActivity(), SerialService.class)); // prevents service destroy on unbind from recreated activity caused by orientation change
}
@Override
public void onStop() {
if(service != null && !getActivity().isChangingConfigurations())
service.detach();
super.onStop();
}
@SuppressWarnings("deprecation") // onAttach(context) was added with API 23. onAttach(activity) works for all API versions
@Override
public void onAttach(@NonNull Activity activity) {
super.onAttach(activity);
getActivity().bindService(new Intent(getActivity(), SerialService.class), this, Context.BIND_AUTO_CREATE);
}
@Override
public void onDetach() {
try { getActivity().unbindService(this); } catch(Exception ignored) {}
super.onDetach();
}
@Override
public void onResume() {
super.onResume();
if(initialStart && service != null) {
initialStart = false;
getActivity().runOnUiThread(this::connect);
}
}
@Override
public void onServiceConnected(ComponentName name, IBinder binder) {
service = ((SerialService.SerialBinder) binder).getService();
service.attach(this);
if(initialStart && isResumed()) {
initialStart = false;
getActivity().runOnUiThread(this::connect);
}
}
@Override
public void onServiceDisconnected(ComponentName name) {
service = null;
}
/*
* UI
*/
@Override
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_terminal, container, false);
receiveText = view.findViewById(R.id.receive_text); // TextView performance decreases with number of spans
receiveText.setTextColor(getResources().getColor(R.color.colorRecieveText)); // set as default color to reduce number of spans
receiveText.setMovementMethod(ScrollingMovementMethod.getInstance());
sendText = view.findViewById(R.id.send_text);
hexWatcher = new TextUtil.HexWatcher(sendText);
hexWatcher.enable(hexEnabled);
sendText.addTextChangedListener(hexWatcher);
sendText.setHint(hexEnabled ? "HEX mode" : "");
View sendBtn = view.findViewById(R.id.send_btn);
sendBtn.setOnClickListener(v -> send(sendText.getText().toString()));
return view;
}
@Override
public void onCreateOptionsMenu(@NonNull Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.menu_terminal, menu);
menu.findItem(R.id.hex).setChecked(hexEnabled);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.clear) {
receiveText.setText("");
return true;
} if (id == R.id.plot){
Intent intent = new Intent(getActivity(), MainActivity2.class);
startActivity(intent);
return true;
}else if (id == R.id.newline) {
String[] newlineNames = getResources().getStringArray(R.array.newline_names);
String[] newlineValues = getResources().getStringArray(R.array.newline_values);
int pos = java.util.Arrays.asList(newlineValues).indexOf(newline);
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setTitle("Newline");
builder.setSingleChoiceItems(newlineNames, pos, (dialog, item1) -> {
newline = newlineValues[item1];
dialog.dismiss();
});
builder.create().show();
return true;
} else if (id == R.id.hex) {
hexEnabled = !hexEnabled;
sendText.setText("");
hexWatcher.enable(hexEnabled);
sendText.setHint(hexEnabled ? "HEX mode" : "");
item.setChecked(hexEnabled);
return true;
} else {
return super.onOptionsItemSelected(item);
}
}
/*
* Serial UI
*/
private void connect() {
try {
BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
BluetoothDevice device = bluetoothAdapter.getRemoteDevice(deviceAddress);
status("connecting...");
connected = Connected.Pending;
SerialSocket socket = new SerialSocket(getActivity().getApplicationContext(), device);
service.connect(socket);
} catch (Exception e) {
onSerialConnectError(e);
}
}
private void disconnect() {
connected = Connected.False;
service.disconnect();
}
private void send(String str) {
if(connected != Connected.True) {
Toast.makeText(getActivity(), "not connected", Toast.LENGTH_SHORT).show();
return;
}
try {
String msg;
byte[] data;
if(hexEnabled) {
StringBuilder sb = new StringBuilder();
TextUtil.toHexString(sb, TextUtil.fromHexString(str));
TextUtil.toHexString(sb, newline.getBytes());
msg = sb.toString();
data = TextUtil.fromHexString(msg);
} else {
msg = str;
data = (str newline).getBytes();
}
SpannableStringBuilder spn = new SpannableStringBuilder(msg '\n');
spn.setSpan(new ForegroundColorSpan(getResources().getColor(R.color.colorSendText)), 0, spn.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
receiveText.append(spn);
service.write(data);
} catch (Exception e) {
onSerialIoError(e);
}
}
private void receive(byte[] data) {
if(hexEnabled) {
receiveText.append("Hello" TextUtil.toHexString(data) '\n');
} else {
String msg = new String(data);
if(newline.equals(TextUtil.newline_crlf) && msg.length() > 0) {
// don't show CR as ^M if directly before LF
msg = msg.replace(TextUtil.newline_crlf, TextUtil.newline_lf);
// special handling if CR and LF come in separate fragments
if (pendingNewline && msg.charAt(0) == '\n') {
Editable edt = receiveText.getEditableText();
if (edt != null && edt.length() > 1)
edt.replace(edt.length() - 2, edt.length(), "");
}
pendingNewline = msg.charAt(msg.length() - 1) == '\r';
}
receiveText.append(TextUtil.toCaretString(msg, newline.length() != 0)); //print out data
}
}
private void status(String str) {
SpannableStringBuilder spn = new SpannableStringBuilder(str '\n');
spn.setSpan(new ForegroundColorSpan(getResources().getColor(R.color.colorStatusText)), 0, spn.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
receiveText.append(spn);
}
/*
* SerialListener
*/
@Override
public void onSerialConnect() {
status("connected");
connected = Connected.True;
}
@Override
public void onSerialConnectError(Exception e) {
status("connection failed: " e.getMessage());
disconnect();
}
@Override
public void onSerialRead(byte[] data) {
receive(data);
}
@Override
public void onSerialIoError(Exception e) {
status("connection lost: " e.getMessage());
disconnect();
}
}
MainActivity2.java 定義了 activity_main2.xml
package de.kai_morich.simple_bluetooth_le_terminal;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;
public class MainActivity2 extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
Toolbar toolbar = findViewById(R.id.toolbar2);
setSupportActionBar(toolbar);
Intent intent = getIntent();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu_plot,menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.dataplot:
Toast.makeText(this, "dataplot", Toast.LENGTH_SHORT).show();
return true;
case R.id.fft:
Toast.makeText(this, "FFT", Toast.LENGTH_SHORT).show();
return true;
case R.id.data:
Toast.makeText(this, "DATA", Toast.LENGTH_SHORT).show();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
}
activity_main2.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity2">
<androidx.appcompat.widget.Toolbar
android:id="@ id/toolbar2"
android:layout_width="409dp"
android:layout_height="wrap_content"
android:layout_marginStart="1dp"
android:layout_marginEnd="1dp"
android:layout_marginBottom="675dp"
android:background="?attr/colorPrimary"
android:minHeight="?attr/actionBarSize"
android:theme="?attr/actionBarTheme"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
uj5u.com熱心網友回復：
我認為您的工具列被layout_marginBottom = 675dp. 如果您想Toolbar在螢屏頂部顯示，我建議這樣做：
<androidx.appcompat.widget.Toolbar
android:id="@ id/toolbar2"
android:layout_width="0dp"
android:layout_height="?attr/actionBarSize"
android:layout_marginStart="1dp"
android:layout_marginEnd="1dp"
android:background="?attr/colorPrimary"
android:theme="?attr/actionBarTheme"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
轉載請註明出處，本文鏈接：https://www.uj5u.com/qiye/479407.html