[Android learning] Four storage methods for Android data (2) -- File

File: A File (I/O) storage method, which is commonly used to store a large amount of data. However, updating data is difficult.

The following program demonstrates how to read and write files in the application data folder. The interface of this program is as simple as it contains only two text input boxes and two buttons: the first text box and the button are used to process the input; the second text box is used for data processing. The Code is as follows:

 

package com.ye_yun_lin.filetest;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.PrintStream;import javax.security.auth.PrivateCredentialPermission;import android.os.Bundle;import android.R.integer;import android.app.Activity;import android.view.Menu;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;public class MainActivity extends Activity {final String FILE_NAME = "MyData";private EditText editText1;private EditText editText2;private Button button1;private Button button2;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);editText1=(EditText)findViewById(R.id.edittext1);button1=(Button)findViewById(R.id.button1);editText2=(EditText)findViewById(R.id.edittext2);button2=(Button)findViewById(R.id.button2);button1.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {write(editText1.getText().toString());editText1.setText("");}});button2.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {editText2.setText(read());}});}private String read(){try {FileInputStream fileInputStream=openFileInput(FILE_NAME);byte[] buff=new byte[1024];int hasRead=0;StringBuilder sBuilder=new StringBuilder("");while ((hasRead=fileInputStream.read(buff))>0) {sBuilder.append(new String(buff,0,hasRead));}fileInputStream.close();return sBuilder.toString();} catch (Exception e) {e.printStackTrace();}return null;}private void write(String content){try {FileOutputStream fileOutputStream=openFileOutput(FILE_NAME, MODE_APPEND);PrintStream printStream=new PrintStream(fileOutputStream);printStream.println(content);printStream.close();} catch (Exception e) {e.printStackTrace();}}}

 

 

Example: SD card file browser:

When the program starts, the system obtains all the files and folders in the/mnt/sdcard directory and displays them using ListView. When you click the specified list of ListView, the system displays all the folders and files in the list.

The program's interface layout file is as follows:

 

Main Code:

 

 

Package com. ye_yun_lin.sdcard; import java. io. file; import java. io. fileOutputStream; import java. io. IOException; import java. util. arrayList; import java. util. hashMap; import java. util. list; import java. util. map; import android. OS. bundle; import android. r. integer; import android. app. activity; import android. view. menu; import android. view. view; import android. view. view. onClickListener; import android. widget. adapterView; import android. widget. adapterView. onItemClickListener; import android. widget. button; import android. widget. listView; import android. widget. simpleAdapter; import android. widget. textView; import android. widget. toast; public class MainActivity extends Activity {private TextView textView; private ListView; private Button button; private File currentParent; private File [] currentFiles; @ Overrideprotected void onCreate (Bundle savedInstanceState) {super. onCreate (savedInstanceState); setContentView (R. layout. activity_main); textView = (TextView) findViewById (R. id. path); listView = (ListView) findViewById (R. id. list); button = (Button) findViewById (R. id. parent); File root = new File ("/mnt/sdcard/"); if (root. exists () {currentParent = root; currentFiles = root. listFiles (); inflateListView (currentFiles);} listView. setOnItemClickListener (new OnItemClickListener () {@ Overridepublic void onItemClick (AdapterView
 Parent, View view, int position, long id) {if (currentFiles [position]. isFile () return; File [] tmp = currentFiles [position]. listFiles (); if (tmp = null | tmp. length = 0) {Toast. makeText (MainActivity. this, "the current path is not accessible or there are no files under this path", Toast. LENGTH_SHORT);} else {currentParent = currentFiles [position]; currentFiles = tmp; inflateListView (currentFiles) ;}}); button. setOnClickListener (new OnClickListener () {@ Overridepublic void OnClick (View v) {try {if (! CurrentParent. getCanonicalPath (). equals ("/mnt/sdcard") {currentParent = currentParent. getParentFile (); currentFiles = currentParent. listFiles (); inflateListView (currentFiles) ;}} catch (IOException e) {e. printStackTrace () ;}});} private void inflateListView (File [] files) {List
 
  
> ListItemsListView = new ArrayList
  
   
> (); For (int I = 0; I
   
    
ListItemMap = new HashMap
    
     
(); If (files [I]. isDirectory () {listItemMap. put ("icon", R. drawable. folder);} else {listItemMap. put ("icon", R. drawable. file);} listItemMap. put ("fileName", files [I]. getName (); listItemsListView. add (listItemMap);} SimpleAdapter simpleAdapter = new SimpleAdapter (this, listItemsListView, R. layout. line, new String [] {"icon", "fileName"}, new int [] {R. id. icon, R. id. file_name}); listView. setAdapter (simpleAdapter); try {textView. setText ("current path:" + currentParent. getCanonicalPath ();} catch (IOException e) {e. printStackTrace ();}}}