本文概述
Android外部存储空间是我们执行读写操作的存储空间。外部存储器中的文件存储在/ sdcard或/ storage文件夹等中。保存在外部存储器中的文件是可读的, 并且可由用户修改。
在访问应用程序外部存储中的文件之前, 我们应检查设备中外部存储的可用性。
写入外部存储中的文件
java.io包提供openFileOutput()方法, 该方法返回FileOutputStream类的实例, 以将文件写入设备的外部存储中。通过调用getExternalFilesDir()获取仅由你的应用程序使用的目录。要将数据写入文件, 请调用FileOutputStream .write()方法。
var myExternalFile:File = File(getExternalFilesDir(filepath), fileName)
try {
val fileOutPutStream = FileOutputStream(myExternalFile)
fileOutPutStream.write(fileContent.toByteArray())
fileOutPutStream.close()
} catch (e: IOException) {
e.printStackTrace()
}
从外部存储读取文件内容
java.io包提供了openFileInput()方法, 该方法返回FileInputStream类的实例, 并从设备的外部存储读取文件。要从文件读取数据, 请调用BufferedReader()。readLine()。
var myExternalFile:File = File(getExternalFilesDir(filepath), fileName)
val filename = fileName.text.toString()
myExternalFile = File(getExternalFilesDir(filepath), filename)
var fileInputStream =FileInputStream(myExternalFile)
var inputStreamReader: InputStreamReader = InputStreamReader(fileInputStream)
val bufferedReader: BufferedReader = BufferedReader(inputStreamReader)
val stringBuilder: StringBuilder = StringBuilder()
var text: String? = null
while ({ text = bufferedReader.readLine(); text }() != null) {
stringBuilder.append(text)
}
fileInputStream.close()
外部存储访问权限
在AndroidManifest.xml文件中添加以下权限。
Kotlin Android读写外部存储示例
在此示例中, 我们将数据写入外部存储设备中的文件, 并从同一外部存储设备读取相同的文件内容。
activity_main.xml
在activity_main.xml文件中添加以下代码。在此文件中, 为输入文件名, 文件内容添加两个EditText, 并为保存和查看文件内容添加两个Button。
xmlns:app="/apk/res-auto"
xmlns:tools="/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".kotlinexternalstoragereadwrite.MainActivity">
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/textView2"
android:layout_alignParentTop="true"
android:layout_alignStart="@+id/textView2"
android:layout_marginTop="68dp"
android:text="File Name"
android:textAppearance="@style/Base.TextAppearance.AppCompat.Medium"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.027"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.065" />
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/editTextData"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginBottom="36dp"
android:layout_marginLeft="50dp"
android:layout_marginStart="50dp"
android:text="File Data"
android:textAppearance="@style/Base.TextAppearance.AppCompat.Medium"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.027"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView"
app:layout_constraintVertical_bias="0.167" />
android:id="@+id/editTextFile"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/editTextData"
android:layout_alignStart="@+id/editTextData"
android:layout_alignTop="@+id/textView"
android:ems="10"
android:inputType="none" />
android:id="@+id/editTextData"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_below="@+id/editTextFile"
android:layout_marginEnd="37dp"
android:layout_marginRight="37dp"
android:layout_marginTop="30dp"
android:ems="10"
android:inputType="none"
android:lines="5" />
android:id="@+id/button_save"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_marginBottom="68dp"
android:layout_toLeftOf="@+id/editTextData"
android:layout_toStartOf="@+id/editTextData"
android:text="Save" />
android:id="@+id/button_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/button_save"
android:layout_alignEnd="@+id/editTextData"
android:layout_alignRight="@+id/editTextData"
android:layout_marginEnd="43dp"
android:layout_marginRight="43dp"
android:text="View" />
MainActivity.kt
在MainActivity.kt类中添加以下代码。在此类中, 我们将通过单击保存按钮将文件名和数据保存在外部存储器中, 并通过单击查看按钮来检索文件内容。
package .kotlinexternalstoragereadwrite
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 android.os.Environment
import java.io.*
class MainActivity : AppCompatActivity() {
private val filepath = "MyFileStorage"
internal var myExternalFile: File?=null
private val isExternalStorageReadOnly: Boolean get() {
val extStorageState = Environment.getExternalStorageState()
return if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(extStorageState)) {
true
} else {
false
}
}
private val isExternalStorageAvailable: Boolean get() {
val extStorageState = Environment.getExternalStorageState()
return if (Environment.MEDIA_MOUNTED.equals(extStorageState)) {
true
} else{
false
}
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val fileName = findViewById(R.id.editTextFile) as EditText
val fileData = findViewById(R.id.editTextData) as EditText
val saveButton = findViewById(R.id.button_save) as Button
val viewButton = findViewById(R.id.button_view) as Button
saveButton.setOnClickListener(View.OnClickListener {
myExternalFile = File(getExternalFilesDir(filepath), fileName.text.toString())
try {
val fileOutPutStream = FileOutputStream(myExternalFile)
fileOutPutStream.write(fileData.text.toString().toByteArray())
fileOutPutStream.close()
} catch (e: IOException) {
e.printStackTrace()
}
Toast.makeText(applicationContext, "data save", Toast.LENGTH_SHORT).show()
})
viewButton.setOnClickListener(View.OnClickListener {
myExternalFile = File(getExternalFilesDir(filepath), fileName.text.toString())
val filename = fileName.text.toString()
myExternalFile = File(getExternalFilesDir(filepath), filename)
if(filename.toString()!=null && filename.toString().trim()!=""){
var fileInputStream =FileInputStream(myExternalFile)
var inputStreamReader: InputStreamReader = InputStreamReader(fileInputStream)
val bufferedReader: BufferedReader = BufferedReader(inputStreamReader)
val stringBuilder: StringBuilder = StringBuilder()
var text: String? = null
while ({ text = bufferedReader.readLine(); text }() != null) {
stringBuilder.append(text)
}
fileInputStream.close()
//Displaying data on EditText
Toast.makeText(applicationContext, stringBuilder.toString(), Toast.LENGTH_SHORT).show()
}
})
if (!isExternalStorageAvailable || isExternalStorageReadOnly) {
saveButton.isEnabled = false
}
}
}
AndroidManifest.xml
package=".kotlinexternalstoragereadwrite">
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">
输出：
