Android journey -- start and android journey --

Android journey -- start and android journey --

1. File Reading

Io stream reads files and displays

Package com. helloword; import java. io. bufferedReader; import java. io. file; import java. io. fileInputStream; import java. io. fileNotFoundException; import java. io. IOException; import java. io. inputStreamReader; public class ReadFile {private String text = null; private StringBuffer strbuf = null; public void ReadFile (File file File) {// TODO Auto-generated constructor stub // gets the file output stream FileInputStream (FS); try {FD = new FileInputStream (file ); // convert byte stream to bytes stream BufferedReader br = new BufferedReader (new InputStreamReader (FCM); try {text = br. readLine ();} catch (IOException e) {// TODO Auto-generated catch blocke. printStackTrace () ;}} catch (FileNotFoundException e) {// TODO Auto-generated catch blocke. printStackTrace ();} strbuf. append (text); System. out. println (text );}}

The procedure for accessing "data/com. helloword/file" of android is as follows:

　　Open file e to view the Android file.

Open cmd,Go to sdk platform-tool

> Adb shell
$ Su
# Chmod 777/data

　　# Chmod 777/data

public class MainActivity extends Activity {public Button bt =null;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);bt = (Button) findViewById(R.id.btcon);bt.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubFile file = new File("data/data/com.helloword/file");ReadFile readfile = new ReadFile();}});}

　　

2. read/write operations on SD card files

(1) Register in manifest. xml to obtain the read and write permissions of the SD card.

<! -- Create and delete file permissions in SDCard --> <uses-permission android: name = "android. permission. WRITE_EXTERNAL_STORAGE"/> <! -- Write data permission to SDCard --> <uses-permission android: name = "android. permission. MOUNT_UNMOUNT_FILESYSTEMS"/>

(2) When using SDcard for read/write, several static methods under the Environment class will be used:

1: getDataDirectory (): Get the data directory in Android (data folder in SD card)
2: getDownloadCacheDirectory () Get the downloaded cache directory (the download folder in the SD card)
3: getExternalStorageDirectory () the directory for obtaining external storage generally refers to SDcard (/storage/sdcard0)
4: getExternalStorageState () obtains the current status of the external settings, which generally refers to SDcard. MEDIA_MOUNTED (SDcard exists and can be read and written) has other statuses, you can search in the document.

/*** Determine whether the SDCard exists. [when no external SD card is available, the built-in ROM is also recognized as an SD card] ** @ return */public static boolean isSdCardExist () {return Environment. getExternalStorageState (). equals (Environment. MEDIA_MOUNTED );}

　　

* Use the api to obtain the real path of the SD card. Some mobile phone brands will change the path of the SD card.

Environment. getExternalStorageDirectory ();

Read SD card content

　　

// Read the SD card content // use FileInputStream to read the File public String ReadFlieInputString (String FileName) throws IOException {String result = null; file File = new File (FileName ); try {FileInputStream isfile = new FileInputStream (file); byte [] B = new byte [isfile. available ()]; isfile. read (B); result = new String (B); System. out. print ("read successful:" + result);} catch (FileNotFoundException e) {// TODO Auto-generated catch blocke. printSta CkTrace ();} return result;} // use BufferRead to read the public String FileBufferRead (String FileName) throws IOException {String result = null; try {BufferedReader bReader = new BufferedReader (new FileReader (FileName); String oneline = ""; StringBuffer sb = new StringBuffer (); while (oneline = bReader. readLine ())! = Null) {sb. append (oneline);} result = sb. toString (); bReader. close (); System. out. println ("read succeeded");} catch (FileNotFoundException e) {// TODO Auto-generated catch blocke. printStackTrace ();} return result ;}

Write files to the SD card

// Write to the SD card // use FileOutputStream to write to the File public Boolean writeSDFile (String FileName, String content) {boolean result = false; try {file File = new File (Environment. getExternalStorageDirectory (), FileName); // obtain the output stream FileOutputStream fos = new FileOutputStream (file); fos. write (content. getBytes (); fos. close (); System. out. println ("written successfully:"); result = true;} catch (Exception e) {e. printStackTrace ();} return result;} // use buffread to write the SD card public Boolean BufferWriteFile (String FileName, String content) {boolean result = false; try {File file = new File (Environment. getExternalStorageDirectory (), FileName); // The second parameter indicates whether to append the content in BufferedWriter bw = new BufferedWriter (new FileWriter (file, true); bw. write (content); bw. flush (); System. out. println ("successfully written"); result = true;} catch (Exception e) {e. printStackTrace ();} return result ;}

The above content is purely self-developed! Mostly refer to http://blog.csdn.net/mad1989/article/details/37568667