在Android中以xml文件保存列表错误

Question

我已经实现了一个能够检测BLE信号的代码，并在ListView中显示它们(在列表的每个项目中，它将显示名称，地址和rssi)，但当我试图将其保存到xml文件中时，它会发生错误并停止应用程序。

package com.example.newblescan;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import com.example.newblescan.R;
import android.app.Activity;
import android.app.ListActivity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothManager;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ListView;
import android.widget.Toast;
import com.example.newblescan.adapter.BleDevicesAdapter;
 /**
 * Activity for scanning and displaying available Bluetooth LE devices.
 */
public class DeviceScanActivity extends ListActivity {
private static final int REQUEST_ENABLE_BT = 1;
private static final long SCAN_PERIOD = 500;
private BleDevicesAdapter leDeviceListAdapter;
private BluetoothAdapter bluetoothAdapter;
private Scanner scanner;
private Save save;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    getActionBar().setTitle(R.string.title_devices);
    // Use this check to determine whether BLE is supported on the device.  Then you can
    // selectively disable BLE-related features.
    if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
        Toast.makeText(this, R.string.ble_not_supported, Toast.LENGTH_SHORT).show();
        finish();
        return;
    }
    // Initializes a Bluetooth adapter.  For API level 18 and above, get a reference to
    // BluetoothAdapter through BluetoothManager.
    final BluetoothManager bluetoothManager =
            (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
    bluetoothAdapter = bluetoothManager.getAdapter();
    // Checks if Bluetooth is supported on the device.
    if (bluetoothAdapter == null) {
        Toast.makeText(this, R.string.error_bluetooth_not_supported, Toast.LENGTH_SHORT).show();
        finish();
        return;
    }
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.gatt_scan, menu);
    if (scanner == null || !scanner.isScanning()) {
        menu.findItem(R.id.menu_stop).setVisible(false);
        menu.findItem(R.id.menu_scan).setVisible(true);
        menu.findItem(R.id.menu_refresh).setActionView(null);
    } else {
        menu.findItem(R.id.menu_stop).setVisible(true);
        menu.findItem(R.id.menu_scan).setVisible(false);
        menu.findItem(R.id.menu_refresh).setActionView(
                R.layout.actionbar_indeterminate_progress);
    }
    return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.menu_scan:
            leDeviceListAdapter.clear();
            if (scanner == null) {
                scanner = new Scanner(bluetoothAdapter, mLeScanCallback);
                scanner.startScanning();
                invalidateOptionsMenu();
            }
            break;
        case R.id.menu_stop:
            if (scanner != null) {
                save = new Save(leDeviceListAdapter);
                scanner.stopScanning();
                try {
                    save.savedata();
                } catch (FileNotFoundException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                scanner = null;

                invalidateOptionsMenu();
            }
            break;
    }
    return true;
}
@Override
protected void onResume() {
    super.onResume();
    // Ensures Bluetooth is enabled on the device.  If Bluetooth is not currently enabled,
    // fire an intent to display a dialog asking the user to grant permission to enable it.
    if (!bluetoothAdapter.isEnabled()) {
        final Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
        return;
    }
    init();
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    // User chose not to enable Bluetooth.
    if (requestCode == REQUEST_ENABLE_BT) {
        if (resultCode == Activity.RESULT_CANCELED) {
            finish();
        } else {
            init();
        }
    }
    super.onActivityResult(requestCode, resultCode, data);
}
@Override
protected void onPause() {
    super.onPause();
    if (scanner != null) {
        scanner.stopScanning();
        scanner = null;
    }
}
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
    final BluetoothDevice device = leDeviceListAdapter.getDevice(position);
    if (device == null)
        return;
    //final Intent intent = new Intent(this, DeviceServicesActivity.class);
    //intent.putExtra(DeviceServicesActivity.EXTRAS_DEVICE_NAME, device.getName());
    //intent.putExtra(DeviceServicesActivity.EXTRAS_DEVICE_ADDRESS, device.getAddress());
    //startActivity(intent);
}

private void init() {
    if (leDeviceListAdapter == null) {
        leDeviceListAdapter = new BleDevicesAdapter(getBaseContext());
        setListAdapter(leDeviceListAdapter);
    }
    if (scanner == null) {
        scanner = new Scanner(bluetoothAdapter, mLeScanCallback);
        scanner.startScanning();
    }
    invalidateOptionsMenu();
}
// Device scan callback.
private BluetoothAdapter.LeScanCallback mLeScanCallback =
        new BluetoothAdapter.LeScanCallback() {
            @Override
            public void onLeScan(final BluetoothDevice device, final int rssi, byte[] scanRecord) {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        leDeviceListAdapter.addDevice(device, rssi);
                        leDeviceListAdapter.notifyDataSetChanged();
                    }
                });
            }
        };

private static class Scanner extends Thread {
    private final BluetoothAdapter bluetoothAdapter;
    private final BluetoothAdapter.LeScanCallback mLeScanCallback;
    private volatile boolean isScanning = false;
    Scanner(BluetoothAdapter adapter, BluetoothAdapter.LeScanCallback callback) {
        bluetoothAdapter = adapter;
        mLeScanCallback = callback;
    }
    public boolean isScanning() {
        return isScanning;
    }
    public void startScanning() {
        synchronized (this) {
            isScanning = true;
            start();
        }
    }
    public void stopScanning() {
        synchronized (this) {
            isScanning = false;
            bluetoothAdapter.stopLeScan(mLeScanCallback);
        }
    }
    @Override
    public void run() {
        try {
            while (true) {
                synchronized (this) {
                    if (!isScanning)
                        break;
                    bluetoothAdapter.startLeScan(mLeScanCallback);
                }
                sleep(SCAN_PERIOD);
                synchronized (this) {
                    bluetoothAdapter.stopLeScan(mLeScanCallback);
                }
            }
        } catch (InterruptedException ignore) {
        } finally {
            bluetoothAdapter.stopLeScan(mLeScanCallback);
        }
    }
}

public class Save implements Serializable {   
  /**
 * 
 */
private BleDevicesAdapter leDeviceListAdapter;
private static final long serialVersionUID = 1L;
Save(BleDevicesAdapter BLEList) {
    leDeviceListAdapter = BLEList;
}
public void savedata() throws FileNotFoundException{
    String filename = "file.txt";
    FileOutputStream fos = null;
    //Bundle extras = getIntent().getExtras();
    //long timestamp = extras.getLong("currentTime");
    try {
    fos= openFileOutput(filename, Context.MODE_PRIVATE);
    ObjectOutputStream out = new ObjectOutputStream(fos);
    //out.write((int) timestamp);
    out.writeObject(leDeviceListAdapter);
    out.close();
    Toast.makeText(DeviceScanActivity.this, R.string.list_saved, Toast.LENGTH_SHORT).show();
    } catch (FileNotFoundException e){
        e.printStackTrace();
    } catch (IOException e){
        e.printStackTrace();
    }
        }
   }
}

在这里，我希望当我按下按钮时，在R.id中。在menu_stop的情况下，它调用类Save将List保存到xml文件中。下面是我执行应用程序时的日志:

新LOGCAT ! !:

    03-10 10:33:02.426: D/BluetoothAdapter(21891): startLeScan(): null
    03-10 10:33:02.431: D/BluetoothAdapter(21891): onClientRegistered() - status=0 clientIf=4
    03-10 10:33:02.441: D/AbsListView(21891): unregisterIRListener() is called 
    03-10 10:33:02.466: D/AbsListView(21891): unregisterIRListener() is called 
    03-10 10:33:02.486: D/BluetoothAdapter(21891): stopLeScan()
    03-10 10:33:02.521: W/System.err(21891): java.io.NotSerializableException: com.example.newblescan.adapter.BleDevicesAdapter
    03-10 10:33:02.521: W/System.err(21891):    at java.io.ObjectOutputStream.writeNewObject(ObjectOutputStream.java:1364)
    03-10 10:33:02.521: W/System.err(21891):    at java.io.ObjectOutputStream.writeObjectInternal(ObjectOutputStream.java:1671)
    03-10 10:33:02.521: W/System.err(21891):    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:1517)
    03-10 10:33:02.521: W/System.err(21891):    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:1481)
    03-10 10:33:02.521: W/System.err(21891):    at com.example.newblescan.DeviceScanActivity$Save.savedata(DeviceScanActivity.java:295)
    03-10 10:33:02.521: W/System.err(21891):    at com.example.newblescan.DeviceScanActivity.onOptionsItemSelected(DeviceScanActivity.java:116)
    03-10 10:33:02.521: W/System.err(21891):    at android.app.Activity.onMenuItemSelected(Activity.java:2640)
    03-10 10:33:02.521: W/System.err(21891):    at com.android.internal.policy.impl.PhoneWindow.onMenuItemSelected(PhoneWindow.java:1171)
    03-10 10:33:02.521: W/System.err(21891):    at com.android.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:735)
    03-10 10:33:02.521: W/System.err(21891):    at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
    03-10 10:33:02.526: W/System.err(21891):    at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:874)
    03-10 10:33:02.526: W/System.err(21891):    at com.android.internal.view.menu.ActionMenuView.invokeItem(ActionMenuView.java:630)
    03-10 10:33:02.526: W/System.err(21891):    at com.android.internal.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:200)
    03-10 10:33:02.526: W/System.err(21891):    at android.view.View.performClick(View.java:4475)
    03-10 10:33:02.526: W/System.err(21891):    at android.view.View$PerformClick.run(View.java:18786)
    03-10 10:33:02.526: W/System.err(21891):    at android.os.Handler.handleCallback(Handler.java:730)
    03-10 10:33:02.526: W/System.err(21891):    at android.os.Handler.dispatchMessage(Handler.java:92)
    03-10 10:33:02.526: W/System.err(21891):    at android.os.Looper.loop(Looper.java:137)
    03-10 10:33:02.526: W/System.err(21891):    at android.app.ActivityThread.main(ActivityThread.java:5493)
    03-10 10:33:02.526: W/System.err(21891):    at java.lang.reflect.Method.invokeNative(Native Method)
    03-10 10:33:02.526: W/System.err(21891):    at java.lang.reflect.Method.invoke(Method.java:525)
    03-10 10:33:02.526: W/System.err(21891):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209)
    03-10 10:33:02.526: W/System.err(21891):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025)
    03-10 10:33:02.531: W/System.err(21891):    at dalvik.system.NativeStart.main(Native Method)
    03-10 10:33:02.931: D/BluetoothAdapter(21891): stopLeScan()
    03-10 10:33:02.931: D/BluetoothAdapter(21891): stopLeScan()
    03-10 10:33:07.701: D/AbsListView(21891): unregisterIRListener() is called 
    03-10 10:33:07.911: D/AbsListView(21891): onDetachedFromWindow

谁能解决这个错误或把这个代码的更正，它可能是缺失的代码??Pleaseee帮助! !

更新:现在当我按下按钮停止扫描，它停止完美，但我不知道为什么它不保存甚至创建xml文件。而且，它不会因为知道它已被保存而弹出吐司。我更新了上面的代码和日志。有人能解决这个新问题吗??!!!!!!

Answer 1

In savedata()

Toast.makeText(null, R.string.list_saved, Toast.LENGTH_SHORT).show();

在上下文中传递null !？

应该是

Toast.makeText(DeviceScanActivity.this, R.string.list_saved, Toast.LENGTH_SHORT).show();

同时，初始化FileOutputStream变量

FileOutputStream fos = null;

代替

FileOutputStream fos;

Answer 2

在第290行savedata方法中有一个空引用。我看不到你的行号，但试着检查你的getExtras()在你试图使用它之前实际上返回了一些东西。

也可以查看:stackoverflow.com/questions/6065258/how-to-interpret-logcat