该程序实现将字符串保存到文件，读取文件。
首先要获取外部存储写权限
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
?MainActivity.java
package com.example.sdfiledemo;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import android.app.Activity;import android.os.Bundle;import android.os.Environment;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;import android.widget.TextView;import android.widget.Toast;import com.example.sdfiledemo.R.id;public class MainActivity extends Activity { Button write, read; EditText text; TextView lable; File dir, file; FileOutputStream fos; FileInputStream fis; ByteArrayOutputStream baos; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); write = (Button) findViewById(id.button1); read = (Button) findViewById(id.button2); text = (EditText) findViewById(id.editText1); lable = (TextView) findViewById(id.textView1); if (Environment.getExternalStorageState().equals(//查看SD卡是否挂载 Environment.MEDIA_MOUNTED)) { Toast.makeText(MainActivity.this, "SD卡已挂载!", Toast.LENGTH_SHORT) .show(); } dir = new File("/mnt/sdcard/mydir"); file = new File(dir.toString() + "/file.txt"); if (!dir.exists()) {// 若文件夹不存在，则创建目录 dir.mkdirs(); Toast.makeText(MainActivity.this, "mydir文件夹已经创建!", Toast.LENGTH_SHORT).show(); } write.setOnClickListener(new OnClickListener() { public void onClick(View v) { try { fos = new FileOutputStream(file, false);// 不追加 String str = text.getText().toString(); // 直接将字节数组写到文件中，文件若不存在会自动创建 fos.write(str.getBytes()); fos.close();// 关闭文件输出流 Toast.makeText(MainActivity.this, "文件已经写入!", Toast.LENGTH_SHORT).show(); } catch (Exception e) { e.printStackTrace(); } } }); read.setOnClickListener(new OnClickListener() { // 将文件字节读取到字节数组输出流中，以一个字节数组作缓冲 public void onClick(View v) { try { fis = new FileInputStream(file); byte[] buff = new byte[1024];// 设置一个缓冲 baos = new ByteArrayOutputStream(); int len; while ((len = fis.read(buff)) != -1) {// 如果buff没有读完 baos.write(buff, 0, len);// 就将buff内容保存到字节数组输出流中 } byte[] data = baos.toByteArray();// 得到字节数组输出流的数据 baos.close();// 关闭字节数组输出流 fis.close();// 关闭文件输出流 lable.setText(new String(data));// 将读出的内容显示 Toast.makeText(MainActivity.this, "文件已经读出!", Toast.LENGTH_SHORT).show(); } catch (Exception e) { e.printStackTrace(); } } }); }}?布局文件
<RelativeLayout 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" > <LinearLayout android:id="@+id/linearLayout1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentLeft="true" android:layout_alignParentRight="true" android:layout_alignParentTop="true" android:orientation="vertical" > <EditText android:id="@+id/editText1" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentLeft="true" android:layout_alignParentRight="true" android:layout_alignParentTop="true" android:ems="10" > <requestFocus /> </EditText> <Button android:id="@+id/button1" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentLeft="true" android:layout_alignParentRight="true" android:layout_below="@+id/editText1" android:text="Button" /> <TextView android:id="@+id/textView1" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentLeft="true" android:layout_alignParentRight="true" android:layout_below="@+id/linearLayout1" android:text="Large Text" android:textAppearance="?android:attr/textAppearanceLarge" /> <Button android:id="@+id/button2" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="Button" /> </LinearLayout></RelativeLayout>
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