Android 如果在 android lollipop 中关闭蓝牙，ble 应用程序会崩溃

Question

您好，我正在尝试扫描 Android Lollipop 的蓝牙设备。它工作正常但是如果关闭蓝牙然后运行应用程序它会崩溃然后弹出窗口以启用 bluetooth.Ideally 就像它应该弹出窗口以启用蓝牙如果它被打开关闭。

这是方法，应该启用蓝牙：

   private void enableBluetooth() { 
   if(bluetoothAdapter == null) {
     //bluetoothState.setText("Bluetooth NOT supported"); } 
   else if(!bluetoothAdapter.isEnabled()) {
     //bluetoothAdapter.enable(); 
     Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); 
     activity.startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT); 
     } 
   }

开始扫描的代码

public void handleScanStart(View view) {
        foundDevices.clear();
        btArrayAdapter.clear();
        ble.startBleScan();
        scanButton.setEnabled(false);
       stopScanButton.setEnabled(true);
}

启用开始扫描

  public void startBleScan() {
        if(getScanning()) {
           return;
       }

          enableBluetooth();
         scanning = true;


         ScanFilter.Builder filterBuilder = new ScanFilter.Builder();                     //TODO currently default, scans all devices
        ScanSettings.Builder settingsBuilder = new               ScanSettings.Builder();
        settingsBuilder.setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY);
             List<ScanFilter> filters = new ArrayList<ScanFilter>();
                  filters.add(filterBuilder.build());
                   bluetoothLeScanner.startScan(filters, settingsBuilder.build(), scanCallback);

           Log.d(TAG, "Bluetooth is currently scanning...");
                      }

下面是日志文件

    04-29 18:09:11.415: E/AndroidRuntime(26155): FATAL EXCEPTION: main
    04-29 18:09:11.415: E/AndroidRuntime(26155): Process: com.android.androidble5, PID: 26155
    04-29 18:09:11.415: E/AndroidRuntime(26155): java.lang.IllegalStateException: Could not execute method of the activity
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at android.view.View.onClick(View.java:4020)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at android.view.View.performClick(View.java:4780)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at android.view.View$PerformClick.run(View.java:19866)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at android.os.Handler.handleCallback(Handler.java:739)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at android.os.Handler.dispatchMessage(Handler.java:95)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at android.os.Looper.loop(Looper.java:135) 
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at android.app.ActivityThread.main(ActivityThread.java:5254)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at java.lang.reflect.Method.invoke(Native Method)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at java.lang.reflect.Method.invoke(Method.java:372)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
    04-29 18:09:11.415: E/AndroidRuntime(26155): Caused by: java.lang.reflect.InvocationTargetException
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at java.lang.reflect.Method.invoke(Native Method)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at java.lang.reflect.Method.invoke(Method.java:372)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at android.view.View.onClick(View.java:4015)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    ... 10 more
    04-29 18:09:11.415: E/AndroidRuntime(26155): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.bluetooth.le.BluetoothLeScanner.startScan(java.util.List, android.bluetooth.le.ScanSettings, android.bluetooth.le.ScanCallback)' on a null object reference
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at com.android.androidble5.BluetoothUtility.startBleScan(BluetoothUtility.java:204)
    04-29 18:09:11.415: E/AndroidRuntime(26155):    at com.android.androidble5.MyActivity.handleScanStart(MyActivity.java:247)

Answer 1

您可以通过对话框告诉用户蓝牙未启用，然后在他们点击“确定”时为他们启用蓝牙（或者如果他们点击“取消”则不执行任何操作），代码如下：

final BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

if (!bluetoothAdapter.isEnabled()) {
 final AlertDialog.Builder builder = new AlertDialog.Builder(this);
 builder.setTitle("Bluetooth not enabled");
 builder.setMessage("Press OK to enable bluetooth");
 builder.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
  @Override
  public void onClick(DialogInterface dialog, int which) {
   Log.d(TAG, "Enabling bluetooth");
   bluetoothAdapter.enable();
  }
 });
 builder.setNegativeButton(android.R.string.cancel, null);
 builder.show();
}

Answer 2

正确的方法是在开始扫描之前，我们必须检查 BluetoothLeScanner 对象是否为 null，就像我们检查 BluetoothAdapter

样本

if(bluetoothLeScanner != null){
             bluetoothLeScanner.startScan(filters,settingsBuilder.build(),scanCallback);

    }

Android 如果在 android lollipop 中关闭蓝牙，ble 应用程序会崩溃

Android ble app crash if bluetooth is turned off in android lollipop

android

bluetooth