旋转屏幕时可用蓝牙设备的 ListView 变为空白

Question

我有一个 activity，我在其中扫描蓝牙设备并将其放入列表视图中。当我扫描设备时显示良好，但当我旋转屏幕（纵向 <-> 横向）时，列表视图变为空白。

我已经实现了 onSaveInstanceState 方法，但我真的不知道要在 outState.put...

中保存什么

 // implement the broadcast reciever for the BT scanning
    private final BroadcastReceiver btScanBrcastReceiver = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                // Discovery has found a device. Get the BluetoothDevice
                // object and its info from the Intent.
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                mBTDevices.add(device);
                availableDevicesList = new AvailableDevicesList(context, R.layout.device_list_view, mBTDevices);

                lv_list_devices.setAdapter(availableDevicesList);
            }

        }
    };

在onCreate方法中

//perform action when clicking on device scaning
        scan_dv_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // check if the scan in in process
                if(btAdapter.isDiscovering()){
                    // cancel the scanning
                    btAdapter.cancelDiscovery();

                    // for version greater than Lolipop
                    checkBTPermission();

                    // restart it
                    btAdapter.startDiscovery();

                    // register the Broadcast receiver
                    IntentFilter IntentfindDv = new IntentFilter(BluetoothDevice.ACTION_FOUND);
                    registerReceiver(btScanBrcastReceiver, IntentfindDv);
                }
                if(!btAdapter.isDiscovering()){
                    //// for version greater than Lolipop
                    checkBTPermission();

                    // start the scanning
                    btAdapter.startDiscovery();
                    // register the Broadcast receiver
                    IntentFilter IntentfindDv = new IntentFilter(BluetoothDevice.ACTION_FOUND);
                    registerReceiver(btScanBrcastReceiver, IntentfindDv);

                }
            }
        });

Answer 1

可能是您的 activity 在您更改方向（纵向 <-> 横向）时正在重新创建。如果您不想在旋转屏幕时刷新 UI，请在清单文件中使用以下内容，

<activity
android:name=".MainActivity"            
android:configChanges="orientation">

如果您想避免 activity 进行多项活动，请查看下方内容，

android:configChanges Lists configuration changes that the activity will handle itself. When a configuration change occurs at runtime, the activity is shut down and restarted by default, but declaring a configuration with this attribute will prevent the activity from being restarted. Instead, the activity remains running and its onConfigurationChanged() method is called.

https://developer.android.com/guide/topics/manifest/activity-element

  android:configChanges=["mcc", "mnc", "locale",
                         "touchscreen", "keyboard", "keyboardHidden",
                         "navigation", "screenLayout", "fontScale",
                         "uiMode", "orientation", "density",
                         "screenSize", "smallestScreenSize"]

旋转屏幕时可用蓝牙设备的 ListView 变为空白

ListView of available Bluetooth device goes blank while rotating the screen

android

bluetooth

broadcastreceiver