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
}