android之外部文件存储和读取

这次借用上次读写内部存储的代码，只是对将更换文件的读写路径即可。这里需要对获取SDcard的读写权限。

一、AndroidManifest.xml

这里增加了对外部存储设备的读写权限

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="xidian.dy.com.chujia">

<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<uses-permission android:name="android.permission.SEND_SMS"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
</manifest>

二、activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:orientation="vertical"
tools:context="xidian.dy.com.chujia.MainActivity">
<EditText
android:id="@+id/username"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="请输入用户名"/>
<EditText
android:id="@+id/password"
android:inputType="textPassword"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="请输入密码"/>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<CheckBox
android:id="@+id/remember"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="记住用户名和密码"
android:layout_centerVertical="true"/>
<Button
android:id="@+id/login"
android:layout_alignParentRight="true"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="登录"/>
</RelativeLayout>
</LinearLayout>

三、MainActivity.java

package xidian.dy.com.chujia;

import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

public class MainActivity extends AppCompatActivity {

private EditText etUsername;
private EditText etPassword;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button bt = (Button) findViewById(R.id.login);
etUsername = (EditText) findViewById(R.id.username);
etPassword = (EditText) findViewById(R.id.password);
if (bt != null)
bt.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String username = null;
String password = null;
if (etUsername != null)
username = etUsername.getText().toString();
if (etPassword != null)
password = etPassword.getText().toString();
Log.e("Login", "登录成功");
CheckBox cb = (CheckBox) findViewById(R.id.remember);
if (cb != null && cb.isChecked()) {
　　　　　　　　　　　　　　 //这里获取sd卡的目录
File file = new File(Environment.getExternalStorageDirectory(), "info.txt");
PrintWriter pw;
try {
pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file))));
pw.println(username);
pw.println(password);
pw.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
//                            Log.e("MainActivity", "file not found");
}
}
}
});
this.readAccount();
}

public void readAccount() {
File file = new File(Environment.getExternalStorageDirectory(), "info.txt");
if (file.exists()) {
try {
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
String str = br.readLine();
if (etUsername != null)
etUsername.setText(str);
str = br.readLine();
if (etPassword != null)
etPassword.setText(str);
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

四、SDcard外部存储检查

在实际开发中，我们在对SDcard进行操作的时候一定先要检查手机是否有SDcard。然后才能对SD进行读写操作。

if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
//TODO
}