我绝对是android开发的初学者。我尝试制作蓝牙应用 并在启动时崩溃。该应用程序应搜索并连接到用户输入名称的特定设备。我已经捕获了所有异常，但我一无所知。任何帮助，将不胜感激。随附完整代码。 谢谢。
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.bluetooth.*;
import android.widget.*;
import android.util.*;
import android.content.*;
import android.view.View;
import java.io.*;
import java.util.*;
public class MainActivity extends AppCompatActivity {
public BluetoothAdapter adapter = BluetoothAdapter.getDefaultAdapter();
UUID newUUID = UUID.randomUUID();
InputStream inStream;
byte[] buffer = new byte[1024];
public ArrayList<BluetoothDevice> devices = new ArrayList<>();
public TextView text = findViewById(R.id.textView);
public String incomingMessage;
private final BroadcastReceiver mBroadcastReceiver1 = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
// When discovery finds a device
if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
final int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR);
switch (state) {
case BluetoothAdapter.STATE_OFF:
Log.d("", "onReceive: STATE OFF");
break;
case BluetoothAdapter.STATE_TURNING_OFF:
Log.d("", "mBroadcastReceiver1: STATE TURNING OFF");
break;
case BluetoothAdapter.STATE_ON:
Log.d("", "mBroadcastReceiver1: STATE ON");
break;
case BluetoothAdapter.STATE_TURNING_ON:
Log.d("", "mBroadcastReceiver1: STATE TURNING ON");
break;
}
}
}
};
private final BroadcastReceiver mBroadcastReceiver2 = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if (BluetoothAdapter.ACTION_SCAN_MODE_CHANGED.equals(action)) {
int mode = intent.getIntExtra(BluetoothAdapter.EXTRA_SCAN_MODE, BluetoothAdapter.ERROR);
switch (mode) {
//Device is in Discoverable Mode
case BluetoothAdapter.SCAN_MODE_CONNECTABLE_DISCOVERABLE:
Log.d("", "mBroadcastReceiver2: Discoverability Enabled.");
break;
//Device not in discoverable mode
case BluetoothAdapter.SCAN_MODE_CONNECTABLE:
Log.d("", "mBroadcastReceiver2: Discoverability Disabled. Able to receive connections.");
break;
case BluetoothAdapter.SCAN_MODE_NONE:
Log.d("", "mBroadcastReceiver2: Discoverability Disabled. Not able to receive connections.");
break;
case BluetoothAdapter.STATE_CONNECTING:
Log.d("", "mBroadcastReceiver2: Connecting....");
break;
case BluetoothAdapter.STATE_CONNECTED:
Log.d("", "mBroadcastReceiver2: Connected.");
break;
}
}
}
};
private BroadcastReceiver mBroadcastReceiver3 = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
Log.d("", "onReceive: ACTION FOUND.");
if (BluetoothDevice.ACTION_FOUND.equals(action)) {
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
devices.add(device);
Log.d("", "onReceive: " + device.getName() + ": " + device.getAddress());
}
}
};
private final BroadcastReceiver mBroadcastReceiver4 = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if (BluetoothDevice.ACTION_BOND_STATE_CHANGED.equals(action)) {
BluetoothDevice mDevice = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
if (mDevice.getBondState() == BluetoothDevice.BOND_BONDED) {
Log.d("", "BroadcastReceiver: BOND_BONDED.");
}
if (mDevice.getBondState() == BluetoothDevice.BOND_BONDING) {
Log.d("", "BroadcastReceiver: BOND_BONDING.");
}
if (mDevice.getBondState() == BluetoothDevice.BOND_NONE) {
Log.d("", "BroadcastReceiver: BOND_NONE.");
}
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void onCLick(View button) {
IntentFilter m4 = new IntentFilter(BluetoothDevice.ACTION_BOND_STATE_CHANGED);
registerReceiver(mBroadcastReceiver4,m4);
if(adapter==null)
{
Log.d("","Bluetooth is null");
onDestroy();
}
EditText deviceName = findViewById(R.id.editText);
String name = deviceName.getText().toString();
BluetoothDevice targetDevice = null;
if (!adapter.isEnabled()) {
Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableIntent, 1);
IntentFilter BTIntent = new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED);
registerReceiver(mBroadcastReceiver1,BTIntent);
Toast.makeText(getApplicationContext(),"BT TURNED ON",Toast.LENGTH_LONG).show();
Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 0);
startActivity(discoverableIntent);
IntentFilter intentFilter = new IntentFilter(BluetoothAdapter.ACTION_SCAN_MODE_CHANGED);
registerReceiver(mBroadcastReceiver2,intentFilter);
}
Set<BluetoothDevice> paired_devices = adapter.getBondedDevices();
Toast.makeText(getApplicationContext(),"GETTING BONDED DEVICES",Toast.LENGTH_LONG).show();
if (paired_devices.size() > 0) {
for (BluetoothDevice mdevice : paired_devices) {
if (mdevice.getName().equals("name")) {
Toast.makeText(getApplicationContext(),"FOUND DEVICE",Toast.LENGTH_LONG).show();
targetDevice = mdevice;
break;
}
}
}
else
{
Toast.makeText(getApplicationContext(),"SEARCHING DEVICES",Toast.LENGTH_LONG).show();
if(adapter.isDiscovering())
adapter.cancelDiscovery();
adapter.startDiscovery();
IntentFilter deviceFound = new IntentFilter(BluetoothDevice.ACTION_FOUND);
registerReceiver(mBroadcastReceiver3,deviceFound);
for(BluetoothDevice mdevice:devices)
{
if(name.equalsIgnoreCase(mdevice.getName()))
{
targetDevice = mdevice;
}
}
if(devices.size()==0)
{
Toast.makeText(getApplicationContext(),"NO DEVICE FOUND... QUITTING",Toast.LENGTH_LONG).show();
}
}
BluetoothSocket mSocket = null;
try {
assert targetDevice != null;
mSocket = targetDevice.createInsecureRfcommSocketToServiceRecord(newUUID);
} catch (IOException | AssertionError e) {
Toast.makeText(getApplicationContext(),"COULD NOT BE CONNECTED",Toast.LENGTH_LONG).show();
e.printStackTrace();
}
try {
assert mSocket != null;
mSocket.connect();
} catch (IOException|AssertionError e) {
e.printStackTrace();
Toast.makeText(getApplicationContext(),"COULD NOT MAKE CONNECTION",Toast.LENGTH_LONG).show();
}
try {
assert mSocket != null;
inStream = mSocket.getInputStream();
} catch (IOException|AssertionError | NullPointerException e) {
Toast.makeText(getApplicationContext(),"PROBLEM CONNECTING",Toast.LENGTH_LONG).show();
e.printStackTrace();
}
while(true)
{
try {
int bytes = inStream.read(buffer);
incomingMessage = new String(buffer,0,bytes);
} catch (IOException e) {
e.printStackTrace();
break;
}
}
text.setText(incomingMessage);
Toast.makeText(getApplicationContext(),"END OF PROGRAM",Toast.LENGTH_LONG).show();
}
}
[https://i.stack.imgur.com/3v3qI.png] [https://i.stack.imgur.com/42Ge5.png]
按下按钮后logcat崩溃的第二个链接
答案 0 :(得分：0)
在渲染视图之前，您无法通过ID查找视图。如果您在全局级别编写findViewById，那么活动将尝试在设置布局之前加载该视图。
将您的findViewById代码放在setContentView()之后。
![https://i.stack.imgur.com/3v3qI.png]](https://i.stack.imgur.com/3v3qI.png]){kind=link}
package in.ks.widgetClock.defaultClasses.webservice;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.bluetooth.*;
import android.widget.*;
import android.util.*;
import android.content.*;
import android.view.View;
import java.io.*;
import java.util.*;
import in.ks.widgetClock.R;
public class MainActivity extends AppCompatActivity {
public BluetoothAdapter adapter = BluetoothAdapter.getDefaultAdapter();
UUID newUUID = UUID.randomUUID();
InputStream inStream;
byte[] buffer = new byte[1024];
public ArrayList<BluetoothDevice> devices = new ArrayList<>();
public TextView text;
public String incomingMessage;
private final BroadcastReceiver mBroadcastReceiver1 = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
// When discovery finds a device
if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
final int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR);
switch (state) {
case BluetoothAdapter.STATE_OFF:
Log.d("", "onReceive: STATE OFF");
break;
case BluetoothAdapter.STATE_TURNING_OFF:
Log.d("", "mBroadcastReceiver1: STATE TURNING OFF");
break;
case BluetoothAdapter.STATE_ON:
Log.d("", "mBroadcastReceiver1: STATE ON");
break;
case BluetoothAdapter.STATE_TURNING_ON:
Log.d("", "mBroadcastReceiver1: STATE TURNING ON");
break;
}
}
}
};
private final BroadcastReceiver mBroadcastReceiver2 = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if (BluetoothAdapter.ACTION_SCAN_MODE_CHANGED.equals(action)) {
int mode = intent.getIntExtra(BluetoothAdapter.EXTRA_SCAN_MODE, BluetoothAdapter.ERROR);
switch (mode) {
//Device is in Discoverable Mode
case BluetoothAdapter.SCAN_MODE_CONNECTABLE_DISCOVERABLE:
Log.d("", "mBroadcastReceiver2: Discoverability Enabled.");
break;
//Device not in discoverable mode
case BluetoothAdapter.SCAN_MODE_CONNECTABLE:
Log.d("", "mBroadcastReceiver2: Discoverability Disabled. Able to receive connections.");
break;
case BluetoothAdapter.SCAN_MODE_NONE:
Log.d("", "mBroadcastReceiver2: Discoverability Disabled. Not able to receive connections.");
break;
case BluetoothAdapter.STATE_CONNECTING:
Log.d("", "mBroadcastReceiver2: Connecting....");
break;
case BluetoothAdapter.STATE_CONNECTED:
Log.d("", "mBroadcastReceiver2: Connected.");
break;
}
}
}
};
private BroadcastReceiver mBroadcastReceiver3 = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
Log.d("", "onReceive: ACTION FOUND.");
if (BluetoothDevice.ACTION_FOUND.equals(action)) {
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
devices.add(device);
Log.d("", "onReceive: " + device.getName() + ": " + device.getAddress());
}
}
};
private final BroadcastReceiver mBroadcastReceiver4 = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if (BluetoothDevice.ACTION_BOND_STATE_CHANGED.equals(action)) {
BluetoothDevice mDevice = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
if (mDevice.getBondState() == BluetoothDevice.BOND_BONDED) {
Log.d("", "BroadcastReceiver: BOND_BONDED.");
}
if (mDevice.getBondState() == BluetoothDevice.BOND_BONDING) {
Log.d("", "BroadcastReceiver: BOND_BONDING.");
}
if (mDevice.getBondState() == BluetoothDevice.BOND_NONE) {
Log.d("", "BroadcastReceiver: BOND_NONE.");
}
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
text = findViewById(R.id.textView);
}
public void onCLick(View button) {
IntentFilter m4 = new IntentFilter(BluetoothDevice.ACTION_BOND_STATE_CHANGED);
registerReceiver(mBroadcastReceiver4,m4);
if(adapter==null)
{
Log.d("","Bluetooth is null");
onDestroy();
}
EditText deviceName = findViewById(R.id.editText);
String name = deviceName.getText().toString();
BluetoothDevice targetDevice = null;
if (!adapter.isEnabled()) {
Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableIntent, 1);
IntentFilter BTIntent = new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED);
registerReceiver(mBroadcastReceiver1,BTIntent);
Toast.makeText(getApplicationContext(),"BT TURNED ON",Toast.LENGTH_LONG).show();
Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 0);
startActivity(discoverableIntent);
IntentFilter intentFilter = new IntentFilter(BluetoothAdapter.ACTION_SCAN_MODE_CHANGED);
registerReceiver(mBroadcastReceiver2,intentFilter);
}
Set<BluetoothDevice> paired_devices = adapter.getBondedDevices();
Toast.makeText(getApplicationContext(),"GETTING BONDED DEVICES",Toast.LENGTH_LONG).show();
if (paired_devices.size() > 0) {
for (BluetoothDevice mdevice : paired_devices) {
if (mdevice.getName().equals("name")) {
Toast.makeText(getApplicationContext(),"FOUND DEVICE",Toast.LENGTH_LONG).show();
targetDevice = mdevice;
break;
}
}
}
else
{
Toast.makeText(getApplicationContext(),"SEARCHING DEVICES",Toast.LENGTH_LONG).show();
if(adapter.isDiscovering())
adapter.cancelDiscovery();
adapter.startDiscovery();
IntentFilter deviceFound = new IntentFilter(BluetoothDevice.ACTION_FOUND);
registerReceiver(mBroadcastReceiver3,deviceFound);
for(BluetoothDevice mdevice:devices)
{
if(name.equalsIgnoreCase(mdevice.getName()))
{
targetDevice = mdevice;
}
}
if(devices.size()==0)
{
Toast.makeText(getApplicationContext(),"NO DEVICE FOUND... QUITTING",Toast.LENGTH_LONG).show();
}
}
BluetoothSocket mSocket = null;
try {
assert targetDevice != null;
mSocket = targetDevice.createInsecureRfcommSocketToServiceRecord(newUUID);
} catch (IOException | AssertionError e) {
Toast.makeText(getApplicationContext(),"COULD NOT BE CONNECTED",Toast.LENGTH_LONG).show();
e.printStackTrace();
}
try {
assert mSocket != null;
mSocket.connect();
} catch (IOException|AssertionError e) {
e.printStackTrace();
Toast.makeText(getApplicationContext(),"COULD NOT MAKE CONNECTION",Toast.LENGTH_LONG).show();
}
try {
assert mSocket != null;
inStream = mSocket.getInputStream();
} catch (IOException|AssertionError | NullPointerException e) {
Toast.makeText(getApplicationContext(),"PROBLEM CONNECTING",Toast.LENGTH_LONG).show();
e.printStackTrace();
}
while(true)
{
try {
int bytes = inStream.read(buffer);
incomingMessage = new String(buffer,0,bytes);
} catch (IOException e) {
e.printStackTrace();
break;
}
}
text.setText(incomingMessage);
Toast.makeText(getApplicationContext(),"END OF PROGRAM",Toast.LENGTH_LONG).show();
}
}