小编Ton*_*ony的帖子

我正在GenericObjectPool通过放入Cipher池进行研究,以便可以重复使用.

GenericObjectPool<Cipher> pool;

CipherFactory factory = new CipherFactory(); 
this.pool = new GenericObjectPool<Cipher>(factory);
pool.setMaxTotal(10);
pool.setBlockWhenExhausted(true);
pool.setMaxWaitMillis(30 * 1000);

CipherFactory

public class CipherFactory extends BasePooledObjectFactory<Cipher> {

    private boolean running = false;

    @Override
    public Cipher create() throws Exception {
        return Cipher.getInstance("DESede/CBC/NoPadding");
    }

    @Override
    public PooledObject<Cipher> wrap(Cipher arg0) {
        return new DefaultPooledObject<Cipher>(arg0);
    }

    @Override
    public boolean validateObject(PooledObject<Cipher> p) {
        //Ensures that the instance is safe to be returned by the pool
        return true;
    }

    @Override
    public void destroyObject(PooledObject<Cipher> p) { …

我使用了这个库中的演示，它工作得很好。但是当我在我的项目中实施时，我在这一行出现错误

错误：不是常量表达式。const AssetImage(snapshot.data[index]),

我的Container正在包装中InkWell。

  InkWell(
      child: Container(
                 padding:
                      EdgeInsets.zero,
                     height: 150,
                      width: 150,
                      decoration:
                            BoxDecoration(
                                      image: DecorationImage(
                                       image: AssetImage(snapshot.data[index]),
                                            fit: BoxFit .fill),
                                  ),
                           ),
      onTap: () {
               print('The value is ' + snapshot .data[index]);
                    Navigator.push(
                      context,
                      MaterialPageRoute(
                        builder:
                         (context) =>
                            const FullScreenWrapper(imageProvider:const AssetImage(snapshot.data[index]),  // here the error
                                    )));
               },
       ),

这里的打印值

值为/storage/emulated/0/Android/data/xxx/files/Pictures/scaled_1572364487252xxx.jpg

如果我删除const，我会收到其他错误

常量创建的参数必须是常量表达式。尝试使参数成为有效的常量，或使用“new”来调用构造函数。

我什至尝试使用new但无济于事。

我想使用此处描述的迁移工具。

但我得到Error: Error when reading 'migrate': No such file or directory

这是我的 dart 版本和错误

xxx@xxx-:~/Desktop/xxx$ dart --version
Dart VM version: 2.4.0 (Unknown timestamp) on "linux_x64"
xxx@xxx-I:~/Desktop/xxx$ dart migrate

Error: Error when reading 'migrate': No such file or directory

pubspec.yaml

version: 1.0.0+1

environment:
  sdk: ">=2.12.0 <3.0.0"

我希望我了解如何didChangeAppLifecycleState正确工作。

我有页面 A 和页面 B 。当我单击页面 B ( Navigator.of(context).pop();) 中的后退设备按钮时，我希望didChangeAppLifecycleState在页面 A中会被调用，但事实并非如此。

页面A

class _ABCState extends State<ABCrList> with WidgetsBindingObserver {
@override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
            ....
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed) {
      setState(() {
        print(...);
      });
    }else{
      print(state.toString());
    }
  }

....

这是initState在页面A。用于调用后端服务的函数。

@override
  void initState() {
    super.initState();  
       _bloc.getList(context);  // return list and populate to ListView
    });
  }

为什么底部导航栏标题不显示？它假设显示在图标下方

class FlutterProject extends StatefulWidget {
  final String title = "Flutter Bottom Tab demo";

  @override
  GoalsListState createState() {
    return GoalsListState();
  }
}

class GoalsListState extends State<FlutterProject>
    with SingleTickerProviderStateMixin {
  int _cIndex = 0;

  void _incrementTab(index) {
    setState(() {
      _cIndex = index;
    });
  }

  final List<Widget> _children = [
    new One(),
    new Two(),
    new Three(),
    new Four(),
    new More()
  ];

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        body: _children[_cIndex],
        bottomNavigationBar: BottomNavigationBar(
          currentIndex: _cIndex,
          type: BottomNavigationBarType.shifting,
          items: [
            BottomNavigationBarItem(
                icon:
                    Icon(Icons.graphic_eq, …

这是什么类型的日期格式？

2020-03-26T00:57:08.000+08:00

我正在使用DateFormat类

 DateTime dateTime = DateTime.now();

 print(dateTime.toIso8601String());
 print(dateTime.toLocal());
 print(dateTime.toUtc());

输出

I/flutter (20667): 2020-03-26T01:34:20.826589
I/flutter (20667): 2020-03-26 01:34:20.826589
I/flutter (20667): 2020-03-25 17:34:20.826589Z

我想要一个像我显示的第一个输出一样的日期格式，后面有+08:00。我应该使用哪个？

错误Error incompatible types: android.app.FragmentManager cannot be converted to android.support.v4.app.FragmentManager让我疯了.

在我的应用程序中,我有3个导航抽屉项目timesheet,claim并view在MainActivity中创建.现在,我想添加两个tabs与swipe view的view项目.

MainActivity //用于导航抽屉

   import android.app.Fragment;
   import android.app.FragmentManager;
   private void selectItem(int position) {

            Fragment fragment = null;

            switch (position) {
                case 0:
                    fragment=new TimeSheet();
                    break;
                case 1:

                    fragment=new Claims1();
                    break;

                case 2:
                    fragment=new Viewview();
                    break;

                default:
                    break;
            }

TabsFragmentPagerAdapter.java

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;

public class TabsFragmentPagerAdapter extends FragmentPagerAdapter {

    public TabsFragmentPagerAdapter(FragmentManager fm) {
        super(fm);
        // …

跟进此问题，LogBack Syslog无法正常工作

我使用下面的命令syslog在ubuntu16.04中查看，但得到以下结果。这是正确的观看方式吗？

user@xxx:~$ tail -f /var/log/syslog Jun  6 23:08:50 xxx systemd[1]:
Starting Hostname Service... Jun  6 23:08:50 xxx dbus[889]: [system]
Successfully activated service 'org.freedesktop.hostname1' Jun  6
23:08:50 xxx systemd[1]: Started Hostname Service. Jun  6 23:09:41 xxx
gnome-session[2645]: (nautilus:2860): Gtk-WARNING **: Attempting to
read the recently used resources file at
'/home/xxx/.local/share/recently-used.xbel', but the parser failed:
Failed to open file '/home/xxx/.local/share/recently-used.xbel':
Permission denied. Jun  6 23:09:41 xxx org.gtk.vfs.Daemon[2508]:
(gvfsd-recent:15282): Gtk-WARNING **: Attempting to read the recently …

我想在颤振中绘制折线图。我遵循本教程，如果日期和月份不同，它可以正常工作。

但是为什么如果它只有一个日期和一个点，图表会变成这个？

代码

/// Timeseries chart example
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
        title: 'My app', // used by the OS task switcher
        theme: ThemeData(
          accentIconTheme: const IconThemeData.fallback().copyWith(
            color: Colors.white,
          ),
          primaryTextTheme: TextTheme(title: TextStyle(color: Colors.white)),
          primarySwatch: Colors.orange,
          primaryIconTheme: const IconThemeData.fallback().copyWith(
            color: Colors.white,
          ),
        ),
        home: SimpleTimeSeriesChart()),
  );
}

class SimpleTimeSeriesChart extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    var seriesList = List<Data>();

    seriesList.add(Data(DateTime(2020, 03, 12), int.parse("50")));

    return Scaffold(
        appBar: AppBar(
          title: Text("Graph"),
        ), …

我正在尝试检索SQLite值并加载到listView MainActivity.我正在按照本教程.

但是,当我的应用程序刚刚开始时,它崩溃并显示出来Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference.

好像我还没有初始化listView.setAdapter.我检查了教程,仍然无法弄清楚我在这里错过了什么.

活动A.

public class MainActivity extends AppCompatActivity {

    InfoAPI sqlcon;
    private SimpleCursorAdapter dataAdapter;
    private SQLiteDatabase database;
    private MyDatabaseHelper dbHelper;
    private ListView listView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        listView=(ListView)findViewById(R.id.listView2);
        setContentView(R.layout.activity_main);
        dbHelper = new MyDatabaseHelper(this);
        sqlcon = new InfoAPI(this);
        BuildList();

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action …

我正在尝试navigation drawer在我的应用程序中创建。在我的一个navigation drawer item，View我希望它有2个tabs与swipe view功能。我可以单独创建它们，但是当我尝试在 1 中执行时，出现错误。

MainActivity // 用于导航抽屉项

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;

private void selectItem(int position) {

        Fragment fragment = null;

        switch (position) {
            case 0:
                fragment=new Information();
                break;
            case 1:

                fragment=new Claims1();
                Bundle bundle=new Bundle();
                bundle.putLong("ab",WorkDetailsTable.ab);
                fragment.setArguments(bundle);
                break;

            case 2:
                fragment=new ViewView();
                break;

            default:
                break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit(); 

            mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(mNavigationDrawerItemTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);

        } else {
            Log.e("MainActivity", "Error …

我的闹钟设计布局listView如下图所示.

custom_row_view

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <RelativeLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:paddingTop="10dp">

            <TextView
                android:id="@+id/time"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textSize="30sp"
                android:text="Time"
                android:paddingLeft="40dp"
                android:paddingTop="15dp"
                android:textColor="@color/black"
                android:textStyle="bold"
                />

            <ToggleButton
                android:id="@+id/switchAlarm"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textOff=""
                android:textOn=""
                android:layout_marginLeft="200dp"
                android:drawableTop="@mipmap/switch_alarm"
                />



        </RelativeLayout>

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:paddingLeft="10dp"
            android:textAppearance="?android:attr/textAppearanceSmall"
            android:text="Text"
            android:id="@+id/textView" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:paddingLeft="5dp"
            android:textAppearance="?android:attr/textAppearanceSmall"
            android:text="Text"
            android:layout_marginRight="@+id/textView"
            android:id="@+id/textView1" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:paddingLeft="5dp"
                android:textAppearance="?android:attr/textAppearanceSmall"
                android:text="Text"
                android:layout_marginRight="@+id/textView1"
                android:id="@+id/textView2" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:paddingLeft="5dp"
                android:textAppearance="?android:attr/textAppearanceSmall"
                android:text="Text"
                android:layout_marginRight="@+id/textView2"
                android:id="@+id/textView3" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:paddingLeft="5dp"
                android:textAppearance="?android:attr/textAppearanceSmall" …

我通过使用以下代码保存图像uri

 public void insert (Uri image) throws SQLiteException {
        SQLiteDatabase database = mdb.getWritableDatabase();
        ContentValues cv = new ContentValues();
        try {
            InputStream iStream = getContentResolver().openInputStream(image);
            byte[] inputData = com.example.tony.monthlyexpenses.Utils.getBytes(iStream);
            cv.put(MyDatabaseHelper.KEY_IMAGE,inputData);
        }catch(IOException ioe)
        {
            Log.e("A", "<saveImageInDB> Error : " + ioe.getLocalizedMessage());
        }
        database.insert(MyDatabaseHelper.TABLE_EXPENSES, null, cv);
        database.close();
    }

实用程序

    public static Bitmap getImage(byte[] image) {
            return BitmapFactory.decodeByteArray(image, 0, image.length);
        }

 public static byte[] getBytes(InputStream inputStream) throws IOException {
        ByteArrayOutputStream byteBuffer = new ByteArrayOutputStream();
        int bufferSize = 1024;
        byte[] buffer = new byte[bufferSize];

        int …