如何检查蓝牙是否以编程方式启用？

There you go:

BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
if (mBluetoothAdapter == null) {
// Device does not support Bluetooth
} else if (!mBluetoothAdapter.isEnabled()) {
// Bluetooth is not enabled :)
} else {
// Bluetooth is enabled
}

With uses-permission

 <uses-permission android:name="android.permission.BLUETOOTH" android:required="false" />

Here I have other alternative as an answer for this question.

First add following lines in your Manifest file.

<uses-feature android:name="android.hardware.BLUETOOTH" android:required="false"/>

Now, where you want to check Bluetooth supportability, use following code.

boolean isBluetoothSupported = getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH);

use can use

BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

for check bt connected

mBluetoothAdapter.getProfileConnectionState(BluetoothHeadset.HEADSET) == BluetoothHeadset.STATE_CONNECTED

for check bt disconnected

mBluetoothAdapter.getProfileConnectionState(BluetoothHeadset.HEADSET) == BluetoothHeadset.STATE_DISCONNECTED

To check Bluetooth state, ON or OFF, programmatically:

    BluetoothAdapter btAdapter = ((Build.VERSION.SDK_INT > Build.VERSION_CODES.JELLY_BEAN_MR1)
?((BluetoothManager)mContext.getSystemService(Context.BLUETOOTH_SERVICE)).getAdapter()
:(BluetoothAdapter.getDefaultAdapter()));


if(btAdapter==null){
return;
}
if(btAdapter.getState()==BluetoothAdapter.STATE_ON){
//Bluetooth is ON
}

You may also listen to Intent action:

BluetoothAdapter.ACTION_STATE_CHANGED

This is how I did it with the help of @xjaphx's answer, slightly simplified version:

 private boolean getBlueToothOn(){
BluetoothAdapter btAdapter = BluetoothAdapter.getDefaultAdapter();
return btAdapter != null && btAdapter.isEnabled();
}


<uses-permission android:name="android.permission.BLUETOOTH" />

public boolean isBluetoothEnabled()
{
BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
return mBluetoothAdapter.isEnabled();


}

with the permission in manifest file:

<uses-permission android:name="android.permission.BLUETOOTH" />

First allow the Permissions from Manifest.

<uses-permission android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>


public class MainActivity extends AppCompatActivity {
    

private BluetoothAdapter mAdapter;
private BluetoothDevice mDevice;
private static final int ACCESS_REQUEST_CODE=100;
private static final int REQUEST_ENABLE_CODE=1;
private AudioRecord mRecord;


@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);


if (mAdapter!=null && mAdapter.isEnabled()){


}
else {
Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableIntent, REQUEST_ENABLE_CODE);
}
}


@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode==REQUEST_ENABLE_CODE){
if (resultCode==RESULT_OK){
println("Bluettoth Enabled");
}
else if (resultCode==RESULT_CANCELED){
println("Bluetooth Not permitted");
finish();
}
}
}
}