把数据存储到外部SD卡上

一、运行效果图

二、核心代码

package com.example.filepersistencetest;

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

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity {
	private Button button;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		button = (Button) this.findViewById(R.id.button);
		button.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View arg0) {
				writeSDcard("Hello，恭喜您数据读取了！");
			}
		});

		if (Environment.MEDIA_MOUNTED.equals(state)) {

			mExternalStorageAvailable = mExternalStorageWriteable = true;
		} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
			// We can only read the media
			mExternalStorageAvailable = true;
			mExternalStorageWriteable = false;
		} else {
			// Something else is wrong. It may be one of many other states, but
			// all we need
			// to know is we can neither read nor write
			mExternalStorageAvailable = mExternalStorageWriteable = false;
		}
	}

	boolean mExternalStorageAvailable = false;
	boolean mExternalStorageWriteable = false;
	String state = Environment.getExternalStorageState();

	// 向SD卡写入数据
	private void writeSDcard(String str) {
		try {
			// 判断是否存在SD卡
			if (Environment.getExternalStorageState().equals(
					Environment.MEDIA_MOUNTED)) {
				// 获取SD卡的目录
				File sdDire = Environment.getExternalStorageDirectory();
				FileOutputStream outFileStream = new FileOutputStream(
						sdDire.getCanonicalPath() + "/test.txt");
				outFileStream.write(str.getBytes());
				outFileStream.close();
				Toast.makeText(this, "数据保存到text.txt文件了", Toast.LENGTH_LONG)
						.show();
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	// 要加权限
	void createExternalStoragePrivateFile() {
		File file = new File(getExternalFilesDir(null), "");
		try {
			InputStream is = getResources()
					.openRawResource((Integer) null);
			OutputStream os = new FileOutputStream(file);
			byte[] data = new byte[is.available()];
			is.read(data);
			os.write(data);
			is.close();
			os.close();
		} catch (IOException e) {
			Log.w("ExternalStorage", "Error writing " + file, e);
		}
	}

	// 要加权限
	void deleteExternalStoragePrivateFile() {
		File file = new File(getExternalFilesDir(null), "");
		if (file != null) {
			file.delete();
		}
	}

	boolean hasExternalStoragePrivateFile() {
		File file = new File(getExternalFilesDir(null), "");
		if (file != null) {
			return file.exists();
		}
		return false;
	}

}

三、遇到的问题。
刚开始不知道如何实现向外部sd卡中写入数据，上网百度，查看别人的博客还参考第一行代码。最后实现。