Android存儲和加載本地文件（外部存儲設(shè)備）

有時候應(yīng)用需要將數(shù)據(jù)寫入到設(shè)備的外部存儲上。列如，需要同其他應(yīng)用或用戶共享音樂、圖片或者網(wǎng)絡(luò)下載資料時，保存在外部設(shè)備的數(shù)據(jù)共享起來要比較方便。而且，外部設(shè)備通常具有更大的存儲空間。

我們可以通過android.os.Environment.getExternalStorageDirectory()方法獲取sdCard的路徑。再在此路徑下創(chuàng)建一個MyFiles的文件，將數(shù)據(jù)保存在MyFiles文件夾下。

下面就展示如何在外部存儲設(shè)備中存儲和加載本地文件：

1、創(chuàng)建一個名為 DataStorage的工程

2、準(zhǔn)備好布局文件（activity_data_storage.xml）

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/data_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="未操作" />

    <Button
        android:id="@+id/save_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="保存數(shù)據(jù)" />

    <Button
        android:id="@+id/load_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="加載數(shù)據(jù)" />

</LinearLayout>

3、在AndroidManifest.xml中加入往sdCard寫入文件的權(quán)限

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

4、DataStorageActivity.java

package com.example.datastorage;

import java.io.BufferedReader;
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.Writer;

import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class DataStorageActivity extends ActionBarActivity {

    private static final String FILENAME = "data.txt";
    private static final String TAG = "DataStorageActivity";
    private TextView dataView;
    private Button saveButton;
    private Button loadButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_date_storage);
        dataView = (TextView) findViewById(R.id.data_view);
        saveButton = (Button) findViewById(R.id.save_button);
        loadButton = (Button) findViewById(R.id.load_button);
        setListener();
    }

    private void setListener() {
        saveButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                try {
                    saveData();
                } catch (IOException e) {
                }
                Toast.makeText(DataStorageActivity.this, "保存成功",
                        Toast.LENGTH_SHORT).show();
            }
        });
        loadButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                try {
                    loadData();
                } catch (FileNotFoundException e) {
                } catch (IOException e) {
                }
            }
        });
    }

    public void saveData() throws IOException {

        File sdCard = Environment.getExternalStorageDirectory();
        // 獲取外部存儲設(shè)備（SD卡）的路徑
        Log.i(TAG, sdCard.getAbsolutePath());
        // 查看LogCat,獲取的sd卡的絕對路徑為 /storage/sdcard
        sdCard = new File(sdCard, "/MyFiles");
        sdCard.mkdirs();// 創(chuàng)建MyFiles目錄(可創(chuàng)建多級目錄)
        sdCard = new File(sdCard, FILENAME);
        FileOutputStream out = new FileOutputStream(sdCard);
        Writer writer = new OutputStreamWriter(out);
        try {
            String str = "來自保存在內(nèi)部存儲設(shè)備的數(shù)據(jù)";
            writer.write(str);
        } finally {
            writer.close();
        }
    }

    public void loadData() throws FileNotFoundException, IOException {
        BufferedReader reader = null;
        StringBuilder data = new StringBuilder();
        try {
            File sdCard = Environment.getExternalStorageDirectory();
            sdCard = new File(sdCard, "/MyFiles/" + FILENAME);
            FileInputStream in = new FileInputStream(sdCard);
            reader = new BufferedReader(new InputStreamReader(in));
            String line = new String();
            while ((line = reader.readLine()) != null) {
                data.append(line);
            }
            dataView.setText(data);
        } catch (FileNotFoundException e) {
            dataView.setText("沒有發(fā)現(xiàn)保存的數(shù)據(jù)");
        } finally {
            reader.close();
        }
    }
}

運行程序，點擊保存數(shù)據(jù)按鈕，Toast顯示保存成功字樣后。再點擊加載數(shù)據(jù)按鈕：

可以發(fā)現(xiàn)保存在內(nèi)部存儲設(shè)備的設(shè)備被加載后在TextView顯示。再看文件具體位置：