android 学习笔记有用代码片段(3)

保存恢复ListView当前位置:

private void saveCurrentPosition() {        if (mListView != null) {            int position = mListView.getFirstVisiblePosition();            View v = mListView.getChildAt(0);            int top = (v == null) ? 0 : v.getTop();            //保存position和top        }    }        private void restorePosition() {        if (mFolder != null && mListView != null) {            int position = 0;//取出保存的数据            int top = 0;//取出保存的数据            mListView.setSelectionFromTop(position, top);        }    }

检测字符串中是否包含汉字:

public static boolean checkChinese(String sequence) {        final String format = "[\\u4E00-\\u9FA5\\uF900-\\uFA2D]";        boolean result = false;        Pattern pattern = Pattern.compile(format);        Matcher matcher = pattern.matcher(sequence);        result = matcher.find();        return result;    }

解决Android AVD的方向键DPAD不能用的问题
解决方式如下 :
找到C:\Documents and Settings\Administrator\.android\avd\avd2.avd下的config.ini文件。
修改dpad的no为yes重启即可。

Android 结束进程，关闭程序的方法
android.os.Process.killProcess(pid)只能终止本程序的进程，无法终止其它的

在android2.2版本之后则不能再使用restartPackage()方法，而应该使用killBackgroundProcesses()方法
manager.killBackgroundProcesses(getPackageName());
ActivityManager manager = (ActivityManager)getSystemService(ACTIVITY_SERVICE);
manager.killBackgroundProcesses(getPackageName());
<uses-permission android:name="android.permission.KILL_BACKGROUND_PROCESSES"/>

还有一种最新发现的方法，利用反射调用forceStopPackage来结束进程
Method forceStopPackage = am.getClass().getDeclaredMethod("forceStopPackage", String.class);
forceStopPackage.setAccessible(true);
forceStopPackage.invoke(am, yourpkgname);

android:sharedUserId="android.uid.system"
<uses-permission android:name="android.permission.FORCE_STOP_PACKAGES"></uses-permission>
因为需要用FORCE_STOP_PACKAGES权限，该权限只赋予系统签名级程序

生成程序性能日志：

性能日志：
if (PROFILE_STARTUP) {
android.os.Debug.startMethodTracing(
Environment.getDataDirectory() + "/debug/log");
}
if (PROFILE_STARTUP) {
android.os.Debug.stopMethodTracing();
}
把launcher.trace文件通过DDMS pull到电脑上，在SDK的tools目录里，执行traceview工具来打开launcher.trace 即可看到内容

通过反射机制获取通知栏高度

public static int getStatusBarHeight(Context context){        Class<?> c = null;        Object obj = null;        Field field = null;        int x = 0, statusBarHeight = 0;        try {            c = Class.forName("com.android.internal.R$dimen");            obj = c.newInstance();            field = c.getField("status_bar_height");            x = Integer.parseInt(field.get(obj).toString());            statusBarHeight = context.getResources().getDimensionPixelSize(x);        } catch (Exception e1) {            e1.printStackTrace();        }        return statusBarHeight;    }

自定义view绘制文本计算文本宽度高度：

private Rect mBounds = new Rect();

 String text = String.valueOf(mCount);          mPaint.getTextBounds(text, 0, text.length(), mBounds);          float textWidth = mBounds.width();          float textHeight = mBounds.height();          canvas.drawText(text, getWidth() / 2 - textWidth / 2, getHeight() / 2                  + textHeight / 2, mPaint);

获取异常信息：

 public void getInfo(){          String location="";          StackTraceElement[] stacks = Thread.currentThread().getStackTrace();           location = "类名："+stacks[2].getClassName() + "\n函数名：" + stacks[2].getMethodName()          + "\n文件名：" + stacks[2].getFileName() + "\n行号："          + stacks[2].getLineNumber() + "";          System.out.println(location);      }

launcher 配置：

<intent-filter>       <action android:name="android.intent.action.MAIN" />       <category android:name="android.intent.category.HOME_FIRST" />       <category android:name="android.intent.category.DEFAULT" />       <category android:name="android.intent.category.MONKEY" />    </intent-filter>

android 4.0以后home按键监听方法（观察者模式实现）;

/**  * Home键监听封装  *   * @author way  *   */  public class HomeWatcher {        static final String TAG = "HomeWatcher";      private Context mContext;      private IntentFilter mFilter;      private OnHomePressedListener mListener;      private InnerRecevier mRecevier;        // 回调接口      public interface OnHomePressedListener {          public void onHomePressed();            public void onHomeLongPressed();      }        public HomeWatcher(Context context) {          mContext = context;          mRecevier = new InnerRecevier();          mFilter = new IntentFilter(Intent.ACTION_CLOSE_SYSTEM_DIALOGS);      }        /**      * 设置监听      *       * @param listener      */      public void setOnHomePressedListener(OnHomePressedListener listener) {          mListener = listener;      }        /**      * 开始监听，注册广播      */      public void startWatch() {          if (mRecevier != null) {              mContext.registerReceiver(mRecevier, mFilter);          }      }        /**      * 停止监听，注销广播      */      public void stopWatch() {          if (mRecevier != null) {              mContext.unregisterReceiver(mRecevier);          }      }        /**      * 广播接收者      */      class InnerRecevier extends BroadcastReceiver {          final String SYSTEM_DIALOG_REASON_KEY = "reason";          final String SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS = "globalactions";          final String SYSTEM_DIALOG_REASON_RECENT_APPS = "recentapps";          final String SYSTEM_DIALOG_REASON_HOME_KEY = "homekey";            @Override          public void onReceive(Context context, Intent intent) {              String action = intent.getAction();              if (action.equals(Intent.ACTION_CLOSE_SYSTEM_DIALOGS)) {                  String reason = intent.getStringExtra(SYSTEM_DIALOG_REASON_KEY);                  if (reason != null) {                      L.i(TAG, "action:" + action + ",reason:" + reason);                      if (mListener != null) {                          if (reason.equals(SYSTEM_DIALOG_REASON_HOME_KEY)) {                              // 短按home键                              mListener.onHomePressed();                          } else if (reason                                  .equals(SYSTEM_DIALOG_REASON_RECENT_APPS)) {                              // 长按home键                              mListener.onHomeLongPressed();                          }                      }                  }              }          }      }  }

在对应Activity中实现OnHomePressedListener 接口并注册监听即可：

protected void onResume() {      // TODO Auto-generated method stub      mHomeWatcher = new HomeWatcher(this);      mHomeWatcher.setOnHomePressedListener(this);      mHomeWatcher.startWatch();      super.onResume();  }  protected void onPause() {      // TODO Auto-generated method stub      super.onPause();      mHomeWatcher.setOnHomePressedListener(null);      mHomeWatcher.stopWatch();  }

判断前置摄像，后置摄像是否存在；

/** * 获取前置摄像头 * @return */@TargetApi(9)      private int FindFrontCamera(){          int cameraCount = 0;          Camera.CameraInfo cameraInfo = new Camera.CameraInfo();          cameraCount = Camera.getNumberOfCameras(); // get cameras number                          for ( int camIdx = 0; camIdx < cameraCount;camIdx++ ) {              Camera.getCameraInfo( camIdx, cameraInfo ); // get camerainfo              if ( cameraInfo.facing ==Camera.CameraInfo.CAMERA_FACING_FRONT ) {                   // 代表摄像头的方位，目前有定义值两个分别为CAMERA_FACING_FRONT前置和CAMERA_FACING_BACK后置                 return camIdx;              }          }          return -1;      }  /** * 获取后置摄像头 * @return */    @TargetApi(9)      private int FindBackCamera(){          int cameraCount = 0;          Camera.CameraInfo cameraInfo = new Camera.CameraInfo();          cameraCount = Camera.getNumberOfCameras(); // get cameras number                          for ( int camIdx = 0; camIdx < cameraCount;camIdx++ ) {              Camera.getCameraInfo( camIdx, cameraInfo ); // get camerainfo              if ( cameraInfo.facing ==Camera.CameraInfo.CAMERA_FACING_BACK ) {                   // 代表摄像头的方位，目前有定义值两个分别为CAMERA_FACING_FRONT前置和CAMERA_FACING_BACK后置                 return camIdx;              }          }          return -1;      }

开启摄像头：

int CammeraIndex=FindBackCamera();
if(CammeraIndex==-1){
CammeraIndex=FindFrontCamera();
}
mServiceCamera = Camera.open(CammeraIndex);

java 线程池简单使用案例：

public class ThreadPool {private AtomicBoolean mStopped = new AtomicBoolean(Boolean.FALSE);private ThreadPoolExecutor mQueue;public ThreadPool() {mQueue = new ThreadPoolExecutor(10, 10, 60, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), sThreadFactory);mQueue.allowCoreThreadTimeOut(true);}public void start(Runnable run) {mQueue.execute(run);}public void stop() {if (!mStopped.get()) {mQueue.shutdownNow();mStopped.set(Boolean.TRUE);}}private static final ThreadFactory sThreadFactory = new ThreadFactory() {private final AtomicInteger mCount = new AtomicInteger(1);@Overridepublic Thread newThread(Runnable r) {return new Thread(r, "ThreadPool #" + mCount.getAndIncrement());}};}protected ExecutorService executorService;// 线程池private final int POOL_SIZE = 20;// 单个CPU线程池大小executorService = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() * POOL_SIZE);executorService.execute(client(runnable));executorService.shutdown();newSingleThreadExecutor：创建一个单线程的线程池。这个线程池只有一个线程在工作，也就是相当于单线程串行执行所有任务。如果这个唯一的线程因为异常结束，那么会有一个新的线程来替代它。此线程池保证所有任务的执行顺序按照任务的提交顺序执行。newFixedThreadPool：创建固定大小的线程池。每次提交一个任务就创建一个线程，直到线程达到线程池的最大大小。线程池的大小一旦达到最大值就会保持不变，如果某个线程因为执行异常而结束，那么线程池会补充一个新线程。newCachedThreadPool：创建一个可缓存的线程池。如果线程池的大小超过了处理任务所需要的线程，那么就会回收部分空闲（60秒不执行任务）的线程，当任务数增加时，此线程池又可以智能的添加新线程来处理任务。此线程池不会对线程池大小做限制，线程池大小完全依赖于操作系统（或者说JVM）能够创建的最大线程大小。newScheduledThreadPool：创建一个大小无限的线程池。此线程池支持定时以及周期性执行任务的需求。newSingleThreadExecutor：创建一个单线程的线程池。此线程池支持定时以及周期性执行任务的需求。

android的帮助、about、关于作者、HELP等的提示页面

方法一： AlertDialog ad = new AlertDialog.Builder(SettingPreference.this)                        .setTitle(R.string.about_dlg_title)                        .setMessage(R.string.about_dlg_message)                        .setPositiveButton(getText(R.string.ok), null).create();                ad.show();//加入链接功能                Linkify.addLinks((TextView) ad.findViewById(android.R.id.message),                        Linkify.ALL);方法二：设计一个AboutDialog类继承于AlertDialogpublic class AboutDialog extends AlertDialog {       public AboutDialog(Context context) {           super(context);           final View view = getLayoutInflater().inflate(R.layout.about,                   null);           setButton(context.getText(R.string.close), (OnClickListener) null);           setIcon(R.drawable.icon_about);           setTitle("程序版本   v1.0.0" );           setView(view);       }   布局文件about.xml<?xml version="1.0" encoding="utf-8"?>  <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="fill_parent" android:layout_height="wrap_content">      <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"         android:layout_width="fill_parent" android:layout_height="fill_parent">             <TextView android:layout_height="fill_parent"             android:layout_width="fill_parent" android:text="@string/help_dialog_text"             android:padding="6dip" android:textColor="#FFFFFF" />      </ScrollView>  </FrameLayout>

webView 实现在线解析文档功能（支持office文档，pdf文档，常见文档，存档文件类型（.ZIP 和 .RAR））

private class HelloWebViewClient extends WebViewClient {    @Override    public boolean shouldOverrideUrlLoading(WebView view, String url)    {        String googleDocs = "https://docs.google.com/viewer?url=";                 if (url.endsWith(".pdf"))        {            // Load "url" in google docs        mWebView.loadUrl(googleDocs + url);        }        else        {            // Load all other urls normally.            view.loadUrl(url);        }        return true;    }}

程序崩溃时，重启应用：

//重新配置appliacation <application        android:allowBackup="true"        android:name="com.pioneersoft.aoc.crashexception.CrashApplication"        android:icon="@drawable/icon"        android:theme="@android:style/Theme.NoTitleBar"        android:label="@string/app_name" >public class CrashApplication extends Application {private PendingIntent restartIntent;@Overridepublic void onCreate() {super.onCreate(); // 以下用来捕获程序崩溃异常          Intent intent = new Intent();          // 参数1：包名，参数2：程序入口的activity          intent.setClassName(getPackageName(), "com.pioneersoft.aoc.ui.MainActivity");          restartIntent = PendingIntent.getActivity(getApplicationContext(), 0,                  intent, Intent.FLAG_ACTIVITY_NEW_TASK);          Thread.setDefaultUncaughtExceptionHandler(restartHandler); // 程序崩溃时触发线程 }public UncaughtExceptionHandler restartHandler = new UncaughtExceptionHandler() {          @Override          public void uncaughtException(Thread thread, Throwable ex) {                     AlarmManager mgr = (AlarmManager) getSystemService(Context.ALARM_SERVICE);              mgr.set(AlarmManager.RTC, System.currentTimeMillis() + 5000,                      restartIntent); // 1秒钟后重启应用              Log.e("crash", "intent restart!");            //退出程序         android.os.Process.killProcess(android.os.Process.myPid());         }      };

获取多个可用的存储设备

public static String getExternalStorageDirectory() {//获取所以可用的存储路径Map<String, String> map = System.getenv();String[] values = new String[map.values().size()];map.values().toArray(values);String path = values[values.length - 1];//获取外置存储卡位置if (path.startsWith("/mnt/") && !Environment.getExternalStorageDirectory().getAbsolutePath().equals(path))return path;elsereturn Environment.getExternalStorageDirectory().getAbsolutePath();}

获取存储可用空间：

private static final double KB = 1024.0;      private static final double MB = KB * KB;      private static final double GB = KB * KB * KB;            private static String showFileSize(double size) {          String fileSize;          if (size < KB)              fileSize = size + "B";          else if (size < MB)              fileSize = String.format("%.3f", size / KB) + "KB";          else if (size < GB)              fileSize = String.format("%.3f", size / MB) + "MB";          else              fileSize = String.format("%.3f", size / GB) + "GB";                return fileSize;      }      /** 显示SD卡剩余空间 */      public static String getSdcardAvailable() {          String result = "";          if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {              StatFs sf = new StatFs("/mnt/sdcard");              long blockSize = sf.getBlockSize();              long blockCount = sf.getBlockCount();              long availCount = sf.getAvailableBlocks();              return showFileSize(availCount * blockSize) + " \\ " + showFileSize(blockSize * blockCount);          }          return result;      }          /**     * 获取手机内部可用空间大小     * @return     */    static public long getAvailableInternalMemorySize() {        File path = Environment.getDataDirectory();        StatFs stat = new StatFs(path.getPath());        long blockSize = stat.getBlockSize();        long availableBlocks = stat.getAvailableBlocks();        return availableBlocks * blockSize;    }    /**     * 获取手机内部空间大小     * @return     */    static public long getTotalInternalMemorySize() {        File path = Environment.getDataDirectory();        StatFs stat = new StatFs(path.getPath());        long blockSize = stat.getBlockSize();        long totalBlocks = stat.getBlockCount();        return totalBlocks * blockSize;    }

获取内存使用情况：

  public static String getMemoryUsage() {        ActivityManager activityManager = (ActivityManager) DscaApplication.AppContext.getSystemService(Context.ACTIVITY_SERVICE);        MemoryInfo memoryInfo = new ActivityManager.MemoryInfo();        activityManager.getMemoryInfo(memoryInfo);        long availMemory = memoryInfo.availMem / ONE_M_TO_BYTE;        long totalMemory = memoryInfo.totalMem / ONE_M_TO_BYTE;               return availMemory + "M/" + totalMemory + "M";    }

模拟按键：

public static void simulateKey(final int KeyCode) {    new Thread() {        @Override        public void run() {            try {                Instrumentation inst = new Instrumentation();                inst.sendKeyDownUpSync(KeyCode);            } catch (Exception e) {                Log.e("Exception when sendKeyDownUpSync", e.toString());            }        }    }.start();}@Overridepublic boolean dispatchKeyEvent(KeyEvent event) {dispatchTouchEvent(MotionEvent.obtain(SystemClock.uptimeMillis(), SystemClock.uptimeMillis()+100,                MotionEvent.ACTION_DOWN, 100, 100, 0));return super.dispatchKeyEvent(event);}@Overridepublic boolean dispatchTouchEvent(MotionEvent ev) {dispatchKeyEvent(new KeyEvent (KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_BACK));dispatchKeyEvent(new KeyEvent (KeyEvent.ACTION_UP, KeyEvent.KEYCODE_BACK));dispatchKeyEvent(new KeyEvent(KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_DEL));return super.dispatchTouchEvent(ev);}

/**使用Linux shell命令模拟按键信息     * run linuix shell cmmand      * @param keyCode     */    private void runLinuixShell(final int keyCode){    try{        String keyCommand = "input keyevent " + keyCode;        Runtime runtime = Runtime.getRuntime();        Process proc=runtime.exec(keyCommand);        Log.e("cmdrun","keycode= "+keyCode);       // proc.destroy();        }catch (IOException e){        Log.e("cmderror", e.toString());        }    }

得到file的MIME类型：

// url = file path or whatever suitable URL you want.public static String getMimeType(String url){    String type = null;    String extension = MimeTypeMap.getFileExtensionFromUrl(url);    if (extension != null) {        MimeTypeMap mime = MimeTypeMap.getSingleton();        type = mime.getMimeTypeFromExtension(extension);    }    return type;}

网络相关判断：

/**     * Checks to see if we are connected to a local network, for instance wifi or ethernet     *      * @return true if connected to a local network     */    public static boolean isConnectedToLocalNetwork() {        Context context = Globals.getContext();        ConnectivityManager cm = (ConnectivityManager) context                .getSystemService(Context.CONNECTIVITY_SERVICE);        NetworkInfo ni = cm.getActiveNetworkInfo();        // @TODO: this is only defined starting in api level 13        final int TYPE_ETHERNET = 0x00000009;        return ni != null && ni.isConnected() == true                && (ni.getType() & (ConnectivityManager.TYPE_WIFI | TYPE_ETHERNET)) != 0;    }    /**     * Checks to see if we are connected using wifi     *      * @return true if connected using wifi     */    public static boolean isConnectedUsingWifi() {        Context context = Globals.getContext();        ConnectivityManager cm = (ConnectivityManager) context                .getSystemService(Context.CONNECTIVITY_SERVICE);        NetworkInfo ni = cm.getActiveNetworkInfo();        return ni != null && ni.isConnected() == true                && ni.getType() == ConnectivityManager.TYPE_WIFI;    }

设备唤醒，保持网络连接：

WifiLock wifiLock = null;PowerManager.WakeLock wakeLock; private void takeWakeLock() {        if (wakeLock == null) {            Log.d(TAG, "About to take wake lock");            PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);            // Many (all?) devices seem to not properly honor a            // PARTIAL_WAKE_LOCK,            // which should prevent CPU throttling. This has been            // well-complained-about on android-developers.            // For these devices, we have a config option to force the phone            // into a            // full wake lock.            if (fullWake) {                Log.d(TAG, "Need to take full wake lock");                wakeLock = pm.newWakeLock(PowerManager.FULL_WAKE_LOCK, WAKE_LOCK_TAG);            } else {                wakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, WAKE_LOCK_TAG);            }            wakeLock.setReferenceCounted(false);        }        Log.d(TAG, "Acquiring wake lock");        wakeLock.acquire();    }    private void releaseWakeLock() {        Log.d(TAG, "Releasing wake lock");        if (wakeLock != null) {            wakeLock.release();            wakeLock = null;            Log.d(TAG, "Finished releasing wake lock");        } else {            Log.e(TAG, "Couldn't release null wake lock");        }    }    private void takeWifiLock() {        Log.d(TAG, "Taking wifi lock");        if (wifiLock == null) {            WifiManager manager = (WifiManager) getSystemService(Context.WIFI_SERVICE);            wifiLock = manager.createWifiLock("SwiFTP");            wifiLock.setReferenceCounted(false);        }        wifiLock.acquire();    }    private void releaseWifiLock() {        Log.d(TAG, "Releasing wifi lock");        if (wifiLock != null) {            wifiLock.release();            wifiLock = null;        }    }

日起比较：

public void compareToNowDate(Date date){Date nowdate=new Date();//format date patternSimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//convert to millions secondslong time=DateToLong(StringToDate(formatter.format(nowdate)));long serverTime=DateToLong(date);//convert to secondslong minTime=Math.abs(time-serverTime)/1000;Log.d(getLocalClassName(), "minTime= "+minTime);}private long DateToLong(Date time){SimpleDateFormat st=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//yyyyMMddHHmmssreturn Long.parseLong(st.format(time));}private Date StringToDate(String s){Date time=null;SimpleDateFormat sd=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");try {time=sd.parse(s);} catch (java.text.ParseException e) {System.out.println("输入的日期格式有误！"); e.printStackTrace();}return time;}

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