奉上20个Android很有用的代码片段

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闲话不扯 上代码！（附件里的内容就是代码内容,照顾没时间细看的友友门~~~）

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1：查看是否有存储卡插入
String status=Environment.getExternalStorageState();
if(status.equals(Enviroment.MEDIA_MOUNTED))
{
   说明有SD卡插入
}
2：让某个Activity透明
OnCreate 中不设Layout
this.setTheme(R.style.Theme_Transparent);
以下是 Theme_Transparent的定义（注意transparent_bg是一副透明的图片）
3：在屏幕元素中设置句柄
使用Activity.findViewById来取得屏幕上的元素的句柄. 使用该句柄您可以设置或获取任何该对象外露的
值.
TextView msgTextView = (TextView)findViewById(R.id.msg);
   msgTextView.setText(R.string.push_me);
4:发送短信
            String body=”this is mms demo”;
           Intent mmsintent = new Intent(Intent.ACTION_SENDTO, Uri.fromParts(”smsto”,
number, null));
           mmsintent.putExtra(Messaging.KEY_ACTION_SENDTO_MESSAGE_BODY, body);
           mmsintent.putExtra(Messaging.KEY_ACTION_SENDTO_COMPOSE_MODE, true);
           mmsintent.putExtra(Messaging.KEY_ACTION_SENDTO_EXIT_ON_SENT, true);
            startActivity(mmsintent);
5:发送彩信
           StringBuilder sb = new StringBuilder();
            sb.append(”file://”);
            sb.append(fd.getAbsoluteFile());
            Intent intent = new Intent(Intent.ACTION_SENDTO, Uri.fromParts(”mmsto”, number,
null));
            // Below extra datas are all optional.
            intent.putExtra(Messaging.KEY_ACTION_SENDTO_MESSAGE_SUBJECT, subject);
            intent.putExtra(Messaging.KEY_ACTION_SENDTO_MESSAGE_BODY, body);
            intent.putExtra(Messaging.KEY_ACTION_SENDTO_CONTENT_URI, sb.toString());
            intent.putExtra(Messaging.KEY_ACTION_SENDTO_COMPOSE_MODE, composeMode);
            intent.putExtra(Messaging.KEY_ACTION_SENDTO_EXIT_ON_SENT, exitOnSent);
            startActivity(intent);
7：发送Mail
             mime = “img/jpg”;
            shareIntent.setDataAndType(Uri.fromFile(fd), mime);
            shareIntent.putExtra(Intent.EXTRA_STREAM, Uri.fromFile(fd));
            shareIntent.putExtra(Intent.EXTRA_SUBJECT, subject);
            shareIntent.putExtra(Intent.EXTRA_TEXT, body);
8:注册一个 BroadcastReceiver
registerReceiver(mMasterResetReciever, new IntentFilter(”oms.action.MASTERRESET”));
private BroadcastReceiver mMasterResetReciever = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent){
            String action = intent.getAction();
            if(”oms.action.MASTERRESET”.equals(action)){
                RecoverDefaultConfig();
            }
        }
    };
9:定义ContentObserver，监听某个数据表
private ContentObserver mDownloadsObserver = new DownloadsChangeObserver
(Downloads.CONTENT_URI);
private class DownloadsChangeObserver extends ContentObserver {
        public DownloadsChangeObserver(Uri uri) {
            super(new Handler());
        }
        @Override
        public void onChange(boolean selfChange) {｝ 
        }
  
10:获得 手机UA
public String getUserAgent()
    {
           String user_agent = ProductProperties.get(ProductProperties.USER_AGENT_KEY, null);
            return user_agent;
    }
11：清空手机上Cookie
CookieSyncManager.createInstance(getApplicationContext());
        CookieManager.getInstance().removeAllCookie();
12：建立GPRS 连接
   //Dial the GPRS link.
    private boolean openDataConnection() {
        // Set up data connection.
        DataConnection conn = DataConnection.getInstance();    
            if (connectMode == 0) {
                ret = conn.openConnection(mContext, “cmwap”, “cmwap”, “cmwap”);
            } else {
                ret = conn.openConnection(mContext, “cmnet”, “”, “”);
            }
    }
13：PreferenceActivity 用法
public class Setting extends PreferenceActivity
｛
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.settings)；
    }
｝
Setting.xml:
            android:key=”seting2″
            android:title=”@string/seting2″
            android:summary=”@string/seting2″/>
            android:key=”seting1″
            android:title=”@string/seting1″
            android:summaryOff=”@string/seting1summaryOff”
            android:summaryOn=”@stringseting1summaryOff”/>
14:通过 HttpClient从指定server获取数据
             DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpGet method = new HttpGet(“http://www.baidu.com/1.html”);
            HttpResponse resp;
            Reader reader = null;
            try {
                // AllClientPNames.TIMEOUT
                HttpParams params = new BasicHttpParams();
                params.setIntParameter(AllClientPNames.CONNECTION_TIMEOUT, 10000);
                httpClient.setParams(params);
                resp = httpClient.execute(method);
                int status = resp.getStatusLine().getStatusCode();
                if (status != HttpStatus.SC_OK) return false;
                // HttpStatus.SC_OK;
                return true;
            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } finally {
                if (reader != null) try {
                    reader.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
15:显示toast
Toast.makeText(this._getApplicationContext(), R.string._item, Toast.LENGTH_SHORT).show();
16:在当前Activity中启动另外一个Activity
startActivity(new Intent(this,目标Activity.class));
17:从当前ContentView从查找控件
(Button)findViewById(R.id.btnAbout)   
R.id.btnAbout指控件id。
18:获取屏幕宽高
DisplayMetrics dm = new DisplayMetrics(); 
//获取窗口属性
getWindowManager().getDefaultDisplay().getMetrics(dm);   
int screenWidth = dm.widthPixels;//320 
int screenHeight = dm.heightPixels;//480
19:无标题栏、全屏
//无标题栏 
requestWindowFeature(Window.FEATURE_NO_TITLE); 
//全屏模式 
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
  WindowManager.LayoutParams.FLAG_FULLSCREEN);
注意在setContentView()之前调用，否则无效。
20注册activity
所有用到的Activity都必须在AndroidManifest.xml中注册，否则会报空指针错误。
如：，注意是包名+类名。