牛骨文教育服务平台(让学习变的简单)

有时候应用需要将数据写入到设备的外部存储上。列如,需要同其他应用或用户共享音乐、图片或者网络下载资料时,保存在外部设备的数据共享起来要比较方便。而且,外部设备通常具有更大的存储空间。

我们可以通过android.os.Environment.getExternalStorageDirectory()方法获取sdCard的路径。再在此路径下创建一个MyFiles的文件,将数据保存在MyFiles文件夹下。

下面就展示如何在外部存储设备中存储和加载本地文件:

1、创建一个名为 DataStorage的工程

2、准备好布局文件(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="保存数据" />

    <Button
        android:id="@+id/load_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="加载数据" />
 
</LinearLayout>

3、在AndroidManifest.xml中加入往sdCard写入文件的权限

<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();
		// 获取外部存储设备(SD卡)的路径
		Log.i(TAG, sdCard.getAbsolutePath());
		// 查看LogCat,获取的sd卡的绝对路径为 /storage/sdcard
		sdCard = new File(sdCard, "/MyFiles");
		sdCard.mkdirs();// 创建MyFiles目录(可创建多级目录)
		sdCard = new File(sdCard, FILENAME);
		FileOutputStream out = new FileOutputStream(sdCard);
		Writer writer = new OutputStreamWriter(out);
		try {
			String str = "来自保存在内部存储设备的数据";
			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("没有发现保存的数据");
		} finally {
			reader.close();
		}
	}
}

运行程序,点击保存数据按钮,Toast显示保存成功字样后。再点击加载数据按钮:

可以发现保存在内部存储设备的设备被加载后在TextView显示。再看文件具体位置:

#DONE#