android中的数据存取-方式二：file（文件）
16lz
2021-01-24
在Android系统中，这些文件保存在 /data/data/PACKAGE_NAME/files 目录下。
数据读取
public static String read(Context context, String file) {String data = "";try {FileInputStream stream = context.openFileInput(file);StringBuffer sb = new StringBuffer();int c;while ((c = stream.read()) != -1) {sb.append((char) c);}stream.close();data = sb.toString();} catch (FileNotFoundException e) {} catch (IOException e) {}return data;} 从代码上，看起来唯一的不同就是文件的打开方式了： context.openFileInput(file); Android中的文件读写具有权限控制，所以使用context(Activity的父类)来打开文件，文件在相同的Package中共享。这里的 Package的概念同Preferences中所述的Package，不同于Java中的Package。
数据写入
public static void write(Context context, String file, String msg) {try {FileOutputStream stream = context.openFileOutput(file,Context.MODE_WORLD_WRITEABLE);stream.write(msg.getBytes());stream.flush();stream.close();} catch (FileNotFoundException e) {} catch (IOException e) {}} 在这里打开文件的时候，声明了文件打开的方式。
一般来说，直接使用文件可能不太好用，尤其是，我们想要存放一些琐碎的数据，那么要生成一些琐碎的文件，或者在同一文件中定义一下格式。其实也可以将其包装成Properties来使用：
public static Properties load(Context context, String file) {Properties properties = new Properties();try {FileInputStream stream = context.openFileInput(file);properties.load(stream);} catch (FileNotFoundException e) {} catch (IOException e) {}return properties;}public static void store(Context context, String file, Properties properties) {try {FileOutputStream stream = context.openFileOutput(file,Context.MODE_WORLD_WRITEABLE);properties.store(stream, "");} catch (FileNotFoundException e) {} catch (IOException e) {}} /Chapter09_Data_02/src/com/amaker/test/MainActivity.java
代码package com.amaker.test;/Chapter09_Data_02/res/layout/main.xml
import java.io.FileInputStream;
import java.io.FileOutputStream;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends Activity {
private static final String FILE_NAME = " temp.txt " ;
private Button b1,b2;
private EditText et1,et2;
@Override
public void onCreate(Bundle savedInstanceState) {
super .onCreate(savedInstanceState);
setContentView(R.layout.main);
b1 = (Button)findViewById(R.id.Button01);
b2 = (Button)findViewById(R.id.Button02);
et1 = (EditText)findViewById(R.id.EditText01);
et2 = (EditText)findViewById(R.id.EditText02);
b1.setOnClickListener( new OnClickListener() {
@Override
public void onClick(View v) {
write(et1.getText().toString());
}
});
b2.setOnClickListener( new OnClickListener() {
@Override
public void onClick(View v) {
et2.setText(read());
}
});
}
private String read(){
try {
FileInputStream fis = openFileInput(FILE_NAME);
byte [] buffer = new byte [fis.available()];
fis.read(buffer);
return new String(buffer);
} catch (Exception e) {
e.printStackTrace();
}
return null ;
}
private void write(String content){
try {
FileOutputStream fos = openFileOutput(FILE_NAME, MODE_APPEND);
fos.write(content.getBytes());
fos.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
代码<? xml version = " 1.0 " encoding = " utf-8 " ?>/Chapter09_Data_02/AndroidManifest.xml
< LinearLayout xmlns:android = " http://schemas.android.com/apk/res/android "
android:orientation = " vertical " android:layout_width = " fill_parent "
android:layout_height = " fill_parent " >
< TextView android:layout_width = " fill_parent "
android:layout_height = " wrap_content " android:text = " File Test " />
< EditText android:text = "" android:id = " @+id/EditText01 "
android:layout_width = " fill_parent " android:layout_height = " wrap_content " android:height = " 100px " ></ EditText >
< Button android:id = " @+id/Button01 " android:layout_width = " wrap_content "
android:layout_height = " wrap_content " android:text = " Write " ></ Button >
< EditText android:text = "" android:id = " @+id/EditText02 "
android:layout_width = " fill_parent " android:layout_height = " wrap_content " android:height = " 100px " ></ EditText >
< Button android:id = " @+id/Button02 " android:layout_width = " wrap_content "
android:layout_height = " wrap_content " android:text = " Read " ></ Button >
</ LinearLayout >
代码<? xml version="1.0" encoding="utf-8" ?>
< manifest xmlns:android ="http://schemas.android.com/apk/res/android"
package ="com.amaker.test"
android:versionCode ="1"
android:versionName ="1.0" >
< application android:icon ="@drawable/icon" android:label ="@string/app_name" >
< activity android:name =".MainActivity"
android:label ="@string/app_name" >
< intent-filter >
< action android:name ="android.intent.action.MAIN" />
< category android:name ="android.intent.category.LAUNCHER" />
</ intent-filter >
</ activity >
</ application >
< uses-sdk android:minSdkVersion ="3" />
</ manifest >
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