像内部存储一样,我们能够从设备外部存储器(例如sdcard)中保存或读取数据。 FileInputStream和FileOutputStream类用于读取和写入数据到文件中。
在android外部存储中读写数据的示例
activity_main.xml
从面板上拖出2个edittext,2个textviews和2个按钮,现在activity_main.xml文件将如下所示:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="example.srcmini02.com.externalstorage.MainActivity">
<EditText
android:id="@+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:layout_marginRight="20dp"
android:layout_marginTop="24dp"
android:ems="10" >
<requestFocus />
</EditText>
<EditText
android:id="@+id/editText2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignRight="@+id/editText1"
android:layout_below="@+id/editText1"
android:layout_marginTop="24dp"
android:ems="10" />
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/editText1"
android:layout_alignBottom="@+id/editText1"
android:layout_alignParentLeft="true"
android:text="File Name:" />
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/editText2"
android:layout_alignBottom="@+id/editText2"
android:layout_alignParentLeft="true"
android:text="Data:" />
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/editText2"
android:layout_below="@+id/editText2"
android:layout_marginLeft="70dp"
android:layout_marginTop="16dp"
android:text="save" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/button1"
android:layout_alignBottom="@+id/button1"
android:layout_toRightOf="@+id/button1"
android:text="read" />
</RelativeLayout>
提供外部存储的权限
你需要提供WRITE_EXTERNAL_STORAGE权限。
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="example.srcmini02.com.externalstorage">
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
活动类
让我们编写代码以从android外部存储中写入和读取数据。
package example.srcmini02.com.externalstorage;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
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;
public class MainActivity extends AppCompatActivity {
EditText editTextFileName, editTextData;
Button saveButton, readButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editTextFileName=findViewById(R.id.editText1);
editTextData=findViewById(R.id.editText2);
saveButton=findViewById(R.id.button1);
readButton=findViewById(R.id.button2);
//Performing action on save button
saveButton.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View arg0) {
String filename=editTextFileName.getText().toString();
String data=editTextData.getText().toString();
FileOutputStream fos;
try {
File myFile = new File("/sdcard/"+filename);
myFile.createNewFile();
FileOutputStream fOut = new FileOutputStream(myFile);
OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
myOutWriter.append(data);
myOutWriter.close();
fOut.close();
Toast.makeText(getApplicationContext(), filename + "saved", Toast.LENGTH_LONG).show();
} catch (FileNotFoundException e) {e.printStackTrace();}
catch (IOException e) {e.printStackTrace();}
}
});
//Performing action on Read Button
readButton.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View arg0) {
String filename=editTextFileName.getText().toString();
StringBuffer stringBuffer = new StringBuffer();
String aDataRow = "";
String aBuffer = "";
try {
File myFile = new File("/sdcard/"+filename);
FileInputStream fIn = new FileInputStream(myFile);
BufferedReader myReader = new BufferedReader(
new InputStreamReader(fIn));
while ((aDataRow = myReader.readLine()) != null) {
aBuffer += aDataRow + "\n";
}
myReader.close();
} catch (IOException e) {
e.printStackTrace();
}
Toast.makeText(getApplicationContext(), aBuffer, Toast.LENGTH_LONG).show();
}
});
}
}