Android 数据存储与IO （二）

2.SD卡读写操作

1读写sd卡首先得添加读写权限

2.建一个布局文件，用来接收和展示数据

<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" android:paddingLeft="@dimen/activity_horizontal_margin"     android:paddingRight="@dimen/activity_horizontal_margin"     android:paddingTop="@dimen/activity_vertical_margin"     android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">     <Button         android:id="@+id/buttonWrite"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="写入数据"         android:layout_alignParentTop="true"         android:layout_centerHorizontal="true" />     <EditText         android:id="@+id/edit"         android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:layout_below="@+id/buttonWrite"         android:layout_alignParentLeft="true"         android:layout_alignParentStart="true" />     <Button         android:id="@+id/buttonReade"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="读取数据"         android:layout_below="@+id/edit"         android:layout_alignLeft="@+id/buttonWrite"         android:layout_alignStart="@+id/buttonWrite"         android:layout_marginTop="73dp" />     <TextView         android:id="@+id/textview"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="yu"         android:textSize="20sp"         android:layout_alignParentBottom="true"         android:layout_centerHorizontal="true"         android:layout_marginBottom="167dp" /> </RelativeLayout>

3.

package xiaocool.net.sdtest; import android.os.Bundle; import android.os.Environment; import android.support.v7.app.ActionBarActivity; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; import java.io.BufferedReader; import java.io.File; import java.io.FileInputStream; import java.io.InputStreamReader; import java.io.RandomAccessFile; public class MainActivity extends ActionBarActivity {     private final  String FILE_NAME="/xiaocool.bin";     private Button write,read;     private EditText editText;     private TextView textView;     @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         write=(Button)this.findViewById(R.id.buttonWrite);         read=(Button)this.findViewById(R.id.buttonReade);         editText=(EditText)this.findViewById(R.id.edit);         textView=(TextView)this.findViewById(R.id.textview);         write.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 Write(editText.getText().toString());                 editText.setText("");             }         });         read.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 textView.setText(Read());             }         });     }     //往sd卡写入数据的方法     private void Write(String content){     try{         //如果手机插入了sd卡，而且 具有访问sd卡的权限         if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){             //获取sd卡的目录             File sdCradDir=Environment.getExternalStorageDirectory();             File targetFile=new File(sdCradDir.getCanonicalPath()+FILE_NAME);             //以指定文件创建RandomAccessFile             RandomAccessFile raf=new RandomAccessFile(targetFile,"rw");             //将文件记录指针移到最后             raf.seek(targetFile.length());             //输出文件内容             raf.write(content.getBytes());             //关闭             raf.close();         }     }catch (Exception E){         E.printStackTrace();         }     }     //从sd卡读取数据     private String Read(){        try {            if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){                File sdCardDir=Environment.getExternalStorageDirectory();                //获取制定文件对应的输入流                FileInputStream file=new FileInputStream(sdCardDir.getCanonicalPath()+FILE_NAME);                //将制定的输入流包装成BufferReader                BufferedReader br=new BufferedReader(new InputStreamReader(file));                StringBuilder sb=new StringBuilder("");                String line=null;                //循环读取文件内容                while((line=br.readLine())!=null){                    sb.append(line);                }                //关闭                br.close();                return sb.toString();            }        }catch (Exception E){            E.printStackTrace();        }         return null;     }     @Override     public boolean onCreateOptionsMenu(Menu menu) {         // Inflate the menu; this adds items to the action bar if it is present.         getMenuInflater().inflate(R.menu.menu_main, menu);         return true;     }     @Override     public boolean onOptionsItemSelected(MenuItem item) {         // Handle action bar item clicks here. The action bar will         // automatically handle clicks on the Home/Up button, so long         // as you specify a parent activity in AndroidManifest.xml.         int id = item.getItemId();         //noinspection SimplifiableIfStatement         if (id == R.id.action_settings) {             return true;         }         return super.onOptionsItemSelected(item);     } }