外部存储ExternalStroage(慕课)

 

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>

Android系统私有的外部存储，是随着应用程序的卸载而卸载，公有的外部存储则不会 

 

 

package com.example.testapplication;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

import androidx.annotation.Nullable;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;

public class ExternalActivity extends ApplicationActivity{
    EditText infoEdt;
    TextView txt;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_external);

        infoEdt = findViewById(R.id.info_edt);
        txt = findViewById(R.id.textView6);

        // 外部存储的动态权限
        int permisson = ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);
        if(permisson!= PackageManager.PERMISSION_GRANTED){
            // 动态去申请权限
            ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},1);

        }
    }

    public void operate(View v){
        String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Download/imooc.txt";
        Log.e("TAG",path);
        switch (v.getId()){
            // 保存
            case R.id.save_btn:
                File f = new File(path);
                try{
                    if(!f.exists()){
                        f.createNewFile();
                    }
                    FileOutputStream fos = new FileOutputStream(path,true);
                    String str = infoEdt.getText().toString();
                    fos.write(str.getBytes());

                }catch (IOException e){
                    e.printStackTrace();

                }
                break;
            case R.id.read_btn:
                try {
                    FileInputStream fis = new FileInputStream(path);
                    byte[] b = new byte[1024];
                    int len = fis.read(b);
                    String str2 = new String(b,0,len);
                    txt.setText(str2);
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                break;
        }
    }
}

<?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:layout_height="match_parent">
    <EditText
        android:id="@+id/info_edt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginTop="22dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:maxLines="12"
        android:minLines="12"
        android:hint="请输入待存储的内容..."
        android:gravity="left|top"
         />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        >
        <Button
            android:id="@+id/read_btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginLeft="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginBottom="8dp"
            android:text="读取"
            android:onClick="operate" />

        <Button
            android:id="@+id/save_btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginLeft="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginBottom="8dp"
            android:text="保存"
            android:onClick="operate" />

    </LinearLayout>

    <TextView
        android:id="@+id/textView6"
        android:layout_width="match_parent"
        android:layout_height="176dp"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="32dp"
        />

</LinearLayout>