Android SD卡

一、把数据存储到SD卡上

Android 的存储分为两部分，一部分是内部存储空间，ROM，相当于Windows系统下的电脑内置盘，另一部分是外置存储空间，也就是我们说的SD卡，相当于电脑的U盘之类

找到挂载目录

 

 manifest下

AndroidManifest.xmll

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

    //获取读写SD卡的权限
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        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>-->
        <activity android:name=".SDcardDemoActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

注意： Android6.0 就是API 23之后。APP需要动态获取权限。需要用代码获取权限，这也是为了用户数据更加安全。

SDcardDemoActivity.java

package com.example.logindemo;

import android.Manifest;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import androidx.annotation.Nullable;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

public class SDcardDemoActivity extends Activity implements View.OnClickListener {
    Button mWritedataBtn ;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //设置布局
        setContentView(R.layout.activity_sd_card_layout);

        /**
         * 动态获取权限，Android 6.0 新特性，一些保护权限，除了要在AndroidManifest中声明权限，还要使用如下代码动态获取
         */
        if (Build.VERSION.SDK_INT >= 23) {
            int REQUEST_CODE_CONTACT = 101;
            String[] permissions = {Manifest.permission.WRITE_EXTERNAL_STORAGE};
            //验证是否许可权限
            for (String str : permissions) {
                if (this.checkSelfPermission(str) != PackageManager.PERMISSION_GRANTED) {
                    //申请权限
                    this.requestPermissions(permissions, REQUEST_CODE_CONTACT);
                    return;
                }
            }
        }
        mWritedataBtn=this.findViewById(R.id.write_data_2_sdcard_btn);
        mWritedataBtn.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        if(v == mWritedataBtn){
            //写数据到SD卡上
            File filepath = new File("/storage/self/primary");
            File file = new File(filepath,"info.txt");
            try {
                FileOutputStream fileOutputStream = new FileOutputStream(file);
                fileOutputStream.write("helloSDCard".getBytes());
                fileOutputStream.close();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }
}

activity_sd_card_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:gravity="center"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:text="SD卡例子"
        android:textSize="50dp"
        android:layout_height="wrap_content"/>
    <Button
        android:id="@+id/write_data_2_sdcard_btn"
        android:layout_width="match_parent"
        android:text="向SD卡添加内容"
        android:layout_height="wrap_content">

    </Button>
</LinearLayout>

 获取权限

 困扰了我几个小时，就是因为我一开始在文件写入内容时加了个逗号。。。。。。

二、SD卡的获取路径及判断SD卡是否挂载

 //获取路径
            File externalStorageDirectory=Environment.getExternalStorageDirectory();

else if(v ==mCheckSDcardBtn){
            //点击是否存在SD卡
            String state = Environment.getExternalStorageState();
             if (state.equals(Environment.MEDIA_MOUNTED)) {
                 Log.d(TAG,"SD卡已经挂载");
            }else if(state.equals(Environment.MEDIA_REMOVED)){
                 Log.d(TAG,"SD卡已经删除了");
             }
        }

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:gravity="center"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:text="SD卡例子"
        android:textSize="50dp"
        android:layout_height="wrap_content"/>
    <Button
        android:id="@+id/write_data_2_sdcard_btn"
        android:layout_width="match_parent"
        android:text="向SD卡添加内容"
        android:layout_height="wrap_content">

    </Button>
    <Button
        android:layout_width="match_parent"
        android:text="检查是否存在SD卡"
        android:id="@+id/sd_card_check_btn"
        android:layout_height="wrap_content">

    </Button>
</LinearLayout>

 

 三、获取SD卡的信息

SDcardDemoActivity.java

package com.example.logindemo;

import android.Manifest;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.text.format.Formatter;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import androidx.annotation.Nullable;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.Format;


public class SDcardDemoActivity extends Activity implements View.OnClickListener {
    Button mWritedataBtn ;
    Button mCheckSDcardBtn;
    Button mGetFreeSizeBtn;
    private static String TAG="SDcardDemoActivity";
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //设置布局
        setContentView(R.layout.activity_sd_card_layout);

        /**
         * 动态获取权限，Android 6.0 新特性，一些保护权限，除了要在AndroidManifest中声明权限，还要使用如下代码动态获取
         */
        if (Build.VERSION.SDK_INT >= 23) {
            int REQUEST_CODE_CONTACT = 101;
            String[] permissions = {Manifest.permission.WRITE_EXTERNAL_STORAGE};
            //验证是否许可权限
            for (String str : permissions) {
                if (this.checkSelfPermission(str) != PackageManager.PERMISSION_GRANTED) {
                    //申请权限
                    this.requestPermissions(permissions, REQUEST_CODE_CONTACT);
                    return;
                }
            }
        }
        //初始化控件
        initView();
        //创建监听方法
        initListener();
    }

    private void initListener() {
        mWritedataBtn.setOnClickListener(this);
        mCheckSDcardBtn.setOnClickListener(this);
        mGetFreeSizeBtn.setOnClickListener(this);
    }

    private void initView() {
        mWritedataBtn=this.findViewById(R.id.write_data_2_sdcard_btn);
        mCheckSDcardBtn=this.findViewById(R.id.sd_card_check_btn);
        mGetFreeSizeBtn=this.findViewById(R.id.get_sd_card_free_size_btn);
    }

    @Override
    public void onClick(View v) {
        //获取路径
        File exFile=Environment.getExternalStorageDirectory();
        Log.d(TAG,"Ext-file-path"+exFile);
        if(v == mWritedataBtn){

            //写数据到SD卡上
            File file = new File(exFile,"info.txt");
            try {
                FileOutputStream fileOutputStream = new FileOutputStream(file);
                fileOutputStream.write("helloSDCard".getBytes());
                fileOutputStream.close();
            }catch (Exception e){
                e.printStackTrace();
            }
        }else if(v ==mCheckSDcardBtn){
            //点击是否存在SD卡
            String state = Environment.getExternalStorageState();
             if (state.equals(Environment.MEDIA_MOUNTED)) {
                 Log.d(TAG,"SD卡已经挂载");
            }else if(state.equals(Environment.MEDIA_REMOVED)){
                 Log.d(TAG,"SD卡已经删除了");
             }
        }else if(v ==mGetFreeSizeBtn){
            //获取剩余空间
            long freeSpace = exFile.getFreeSpace();
            //把long类型转化为直观的大小
            String sizeText = Formatter.formatFileSize(this, freeSpace);
            Log.d(TAG,"剩余空间"+sizeText);
        }
    }
}

activity_sd_card_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:gravity="center"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:text="SD卡例子"
        android:textSize="50dp"
        android:layout_height="wrap_content"/>
    <Button
        android:id="@+id/write_data_2_sdcard_btn"
        android:layout_width="match_parent"
        android:text="向SD卡添加内容"
        android:layout_height="wrap_content">

    </Button>
    <Button
        android:layout_width="match_parent"
        android:text="检查是否存在SD卡"
        android:id="@+id/sd_card_check_btn"
        android:layout_height="wrap_content">

    </Button>
    <Button
        android:layout_width="match_parent"
        android:text="获取SD卡所用空间"
        android:id="@+id/get_sd_card_free_size_btn"
        android:layout_height="wrap_content">

    </Button>
</LinearLayout>