课堂整理：写入和读取外部存储文件

layout代码：

<?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="com.example.my.testapp.MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        android:id="@+id/tv_1"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="sp存储"
        android:onClick="bt_onClick"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="sp读取"
        android:onClick="bt1_onClick"/>
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="输入。。。"
        android:id="@+id/et_1"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="bt2_onClick"
        android:text="写入内部文件"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="bt3_onClick"
        android:text="读内部文件"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="bt4_onClick"
        android:text="保存资产文件到内部空间"/>
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/iv_1"
        android:src="@drawable/sword"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="bt5_onClick"
        android:text="设置图片指向内部存储"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="bt6_onClick"
        android:text="写入外部存储文件"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="bt7_onClick"
        android:text="读取外部存储文件"/>

</LinearLayout>

Activity代码：

package com.example.my.testapp;

import android.content.SharedPreferences;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.PrintStream;

public class MainActivity extends AppCompatActivity {

    EditText et_1;
    TextView tv_1;
    ImageView iv_1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        et_1=(EditText)findViewById(R.id.et_1);
        tv_1=(TextView)findViewById(R.id.tv_1);
        iv_1=(ImageView)findViewById(R.id.iv_1);
    }
    public void bt_onClick(View v)
    {
        //1.得到SharedPreferences对象
        SharedPreferences sharedPreferences=getSharedPreferences("abc",MODE_APPEND);

        //2.得到编辑器
        SharedPreferences.Editor editor=sharedPreferences.edit();

        //3.使用Editor添加数据
//        editor.putString("a","abcdef");
//        editor.putString("b","xxxxxx");
//        editor.putLong("long",123456);
        editor.remove("a");

        //4.提交保存
        editor.commit();

        Toast.makeText(MainActivity.this, "保存数据成功。", Toast.LENGTH_SHORT).show();
    }
    //读取
    public void bt1_onClick(View v)
    {
        SharedPreferences sp=getSharedPreferences("abc",MODE_PRIVATE);

        String str=sp.getString("b", null);

        Toast.makeText(MainActivity.this, "key=b"+"value="+str, Toast.LENGTH_SHORT).show();
    }
    //写内部文件
    public void bt2_onClick(View v)
    {
        //从内存里写入文件

        //1.得到内部的存储目录
        try {
            File file = getFilesDir();

            String path = file.getAbsolutePath();

            Toast.makeText(MainActivity.this, "path=" + path, Toast.LENGTH_SHORT).show();

            //2.用输出流写入文件

            FileOutputStream fos = openFileOutput("test.txt", MODE_APPEND);

            //3.写入内容
            PrintStream ps=new PrintStream(fos);

            String str=et_1.getText().toString();

            ps.println(str);
            ps.println("自动换行");
            ps.close();
            fos.close();
            Toast.makeText(MainActivity.this, "保存成功", Toast.LENGTH_SHORT).show();
        }
        catch (Exception e)
        {

        }
    }
    public void  bt3_onClick(View v) {
        try {
            //输入流
            FileInputStream fis = openFileInput("test.txt");

            //1.定义byte[]
            byte[] b =new byte[1024];
            int i=0;//读到的数据长度

            String str1="";

            //2.循环读
            while ((i=fis.read(b))>0)
            {
                String str = new String(b,0,i);

                str1 += str;
            }
            fis.close();

            tv_1.setText(str1);

        }
        catch (Exception ex)
        {

        }
    }
    public void bt4_onClick(View v)
    {
        try {
            //操作assets目录的文件

            //1.得到assetsManager

            AssetManager assetManager = getAssets();

            //2.操作资产目录，边读边写入
            //1) 读文件到内存 inputstream
            InputStream inputStream = assetManager.open("female.png");

            //2) 写文件到目录 outputstream
            FileOutputStream fos=openFileOutput("test.png",MODE_PRIVATE);

            //先读后写
            byte [] b=new byte[1024];
            int i=0;
            while ((i=inputStream.read(b))>0)
            {
                fos.write(b,0,i);
            }
            fos.close();
            inputStream.close();

            Toast.makeText(MainActivity.this, "保存文件成功", Toast.LENGTH_SHORT).show();
        }
        catch (Exception ex)
        {
            Toast.makeText(MainActivity.this, "保存文件出错", Toast.LENGTH_SHORT).show();
        }

    }
    public void bt5_onClick(View v)
    {
        //得到文件路径
        String path=getFilesDir().getAbsolutePath()+"/test.png";

        Toast.makeText(MainActivity.this, "path="+path, Toast.LENGTH_SHORT).show();
        // 从内部存储的图片得到 Bitmap,BitmapFactory.decodeFile("文件途径");
        Bitmap bm= BitmapFactory.decodeFile(path);
        //设置图片视图的图片来源
        iv_1.setImageBitmap(bm);
    }
    public void bt6_onClick(View v)
    {
        //1.判断sd卡是否挂载
       if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))
       {
           //文本框内容
           String str=et_1.getText().toString();
           try {
               //写入
               //1.构造输出流
               //1) 得到文件路径

               //得到SD卡根目录
               //String path=Environment.getExternalStorageDirectory().getCanonicalPath();

               //得到包名对应的目录
               String path=getExternalFilesDir("Music").getCanonicalPath();
               Toast.makeText(MainActivity.this, "path="+path, Toast.LENGTH_SHORT).show();
               //2)构造
               FileOutputStream fos = new FileOutputStream(path + "/test.txt");

               PrintStream ps=new PrintStream(fos);

               ps.print(str);

               ps.close();
               fos.close();
               Toast.makeText(MainActivity.this, "写入外部文件成功", Toast.LENGTH_SHORT).show();
           }
           catch (Exception ex)
           {
               Toast.makeText(MainActivity.this, "存储文件出错", Toast.LENGTH_SHORT).show();
           }
       }
        else
       {
           Toast.makeText(MainActivity.this, "SD卡没有挂载", Toast.LENGTH_SHORT).show();
       }
    }
    public void bt7_onClick(View v)
    {
        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))
        {
            try {
                String path = getExternalFilesDir("Music").getCanonicalPath() + "/test.txt";

                FileInputStream fis= new FileInputStream(path);

                byte [] b=new byte[1024];
                int i=0;

                String str="";

                while ((i=fis.read(b))>0)
                {
                    str+=new String(b,0,i);
                }
                fis.close();

                Toast.makeText(MainActivity.this, "文件内容="+str, Toast.LENGTH_SHORT).show();
            }
            catch (Exception ex)
            {
                Toast.makeText(MainActivity.this, "读取外部文件失败", Toast.LENGTH_SHORT).show();
            }
        }
        else
        {
            Toast.makeText(MainActivity.this, "SD卡没有挂载", Toast.LENGTH_SHORT).show();
        }
    }
}