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);
@Override
public 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AlertDialog
public 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;
@Override
public 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;
else
return 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();
}
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
dispatchTouchEvent(MotionEvent.obtain(SystemClock.uptimeMillis(), SystemClock.uptimeMillis()+100,
MotionEvent.ACTION_DOWN, 100, 100, 0));
return super.dispatchKeyEvent(event);
}
@Override
public 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());
}
}
// 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 pattern
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
//convert to millions seconds
long time=DateToLong(StringToDate(formatter.format(nowdate)));
long serverTime=DateToLong(date);
//convert to seconds
long 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");//yyyyMMddHHmmss
return 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;
}