Android File data storage

First, the File preservation data Introduction

Activity provides the Openfileoutput () method that can be used to output data to a file, and the implementation process is the same as saving data to a file in a J2SE environment. Files can be used to store large amounts of data, such as text, books, audio, and so on.

The file object is suitable for reading or writing large amounts of data in the order from start to finish without skipping. For example, it is suitable for picture files or any content exchanged over the network.

The default location for data storage is:/data/data/< package name >/files/***.***.

All Android devices have two file storage areas: "Internal" and "external" storage. This article mainly stores the data so that the files are stored in the "internal" storage area.

Second, use Method 1. Writing content to a file

Try {       mcontext.openfileoutput (mfilename,context.mode_private);       Fos.write (Info.getbytes ());       Fos.close ();} Catch (Exception e) {       e.printstacktrace ();}

The first parameter of the Openfileoutput () method specifies the file name, cannot contain the path delimiter "/", and if the file does not exist, Android automatically creates it, and the second parameter of the Openfileoutput () method is used to specify the mode of operation.

Operating modes are:

Context.mode_private = 0: For the default mode of operation, the representative changes the file when the private data, can only be accessed by the application itself, in the change mode, the content will overwrite the original file content, if you want to append the new write content to the original file, you can use Context.mode_ APPEND. Context.mode_append = 32768: The mode checks whether the file exists, appends it to the file, or creates a new file. Context.mode_world_readable and context.mode_world_writeable are used to control whether other apps have permission to read and write files. context.mode_world_readable = 1: Indicates that the current file can be read by another application. Context.mode_world_writeable = 2: Indicates that the current file can be written by another application. If you want the file to be read and written by another app, you can pass in context.mode_world_readable+context.mode_world_writeable. Android has its own security model, and when the app (. apk) is installed, the system assigns it a userid, which requires a UserID match when the public is going to access other resources such as files, by default, any file created by the app, Sharedprefrences, the database should be private, and other programs cannot access it. Unless Context.mode_world_readable or context.mode_world_writeable are created at the time of creation, only such other programs can access them normally. 2. Read in the file contents

Try {            = mcontext.openfileinput (mfilename);             New BufferedReader (new  inputstreamreader (FIS));             = reader.readline ();            Fis.close ();             return info;  } Catch (Exception e) {            e.printstacktrace ();  }

Three, small case 1. Add Strings.xml file

   <stringname= "Write_data">Write Data</string>   <stringname= "Read_data">Reading data</string>   <stringname= "File">File</string>

2. Modify the Activity_main.xml file

<TextViewAndroid:layout_width= "Wrap_content"Android:layout_height= "Wrap_content"Android:text= "@string/file"android:layout_gravity= "Center_horizontal"        />    <LinearLayoutAndroid:layout_width= "Match_parent"Android:layout_height= "Wrap_content"android:orientation= "Horizontal"Android:layout_margintop= "@dimen/fab_margin"Android:layout_marginbottom= "@dimen/fab_margin"        >        <ButtonAndroid:id= "@+id/file_write"Android:layout_height= "Wrap_content"Android:layout_width= "0DP"Android:layout_weight= "1"Android:text= "@string/write_data" />        <ButtonAndroid:id= "@+id/file_read"Android:layout_height= "Wrap_content"Android:layout_width= "0DP"Android:layout_weight= "1"Android:text= "@string/read_data" />    </LinearLayout>

3. Add Filedbmanager Class

 PackageCom.zhangmiao.datastoragedemo;ImportAndroid.content.Context;Importandroid.os.Environment;ImportAndroid.util.Log;ImportJava.io.BufferedReader;ImportJava.io.File;ImportJava.io.FileInputStream;ImportJava.io.FileOutputStream;ImportJava.io.InputStreamReader;ImportJava.io.ObjectOutputStream;/*** Created by Zhangmiao on 2016/12/20.*/ Public classFiledbmanager {PrivateFile Mfile; PrivateContext Mcontext; PrivateString mfilename = "MyFile";  PublicFiledbmanager (Context context) {Mcontext=context; }     Public voidWrite (String info) {Try{FileOutputStream fos=Mcontext.openfileoutput (mfilename,context.mode_private);            Fos.write (Info.getbytes ());        Fos.close (); }Catch(Exception e) {e.printstacktrace (); }    }     PublicString Read () {Try{FileInputStream fis=Mcontext.openfileinput (mfilename); BufferedReader Reader=NewBufferedReader (NewInputStreamReader (FIS)); String Info=Reader.readline ();            Fis.close (); returninfo; }Catch(Exception e) {e.printstacktrace (); }        return""; }}

4. Modify Mainactivity

 PackageCom.zhangmiao.datastoragedemo;ImportAndroid.content.ContentResolver;Importandroid.content.ContentValues;ImportAndroid.database.Cursor;ImportAndroid.net.Uri;ImportAndroid.os.Bundle;Importandroid.support.v7.app.AppCompatActivity;ImportAndroid.util.Log;ImportAndroid.view.View;ImportAndroid.widget.Button;ImportAndroid.widget.TextView;Importjava.util.ArrayList;Importjava.util.List; Public classMainactivityextendsAppcompatactivityImplementsView.onclicklistener {PrivateFiledbmanager Mfilemanager;PrivateTextView Mtableinfo; @Overrideprotected voidonCreate (Bundle savedinstancestate) {Super. OnCreate (savedinstancestate); Setcontentview (r.layout.activity_main);Mfilemanager=NewFiledbmanager ( This);Mtableinfo=(TextView) Findviewbyid (r.id.table_info);Filewrite.setonclicklistener ( This); Fileread.setonclicklistener ( This);    }@Override Public voidOnClick (View v) {Switch(V.getid ()) {
 CaseR.id.file_write:mfilemanager.write ("Hello world!");  Break;  CaseR.id.file_read:mtableinfo.settext (Mfilemanager.read ()); Break ;default: Break; }    }}

Android File data storage