Hello. I will start writing articles today. I plan to use Qiita as a programming memo. I have been using Android for about 2 years. I am a graduate student who will start working next year.
This time, I will explain how to save and load files in Android's internal storage. The content of each article about Android storage is slightly different, and I think that some people may get lost, so I will write a standard one.
The development environment is as follows. ＊Android Studio 4.0.1 ＊targetSdkVersion 28 ＊Google Nexus 5x
Android has internal storage and external storage.
■ Internal storage
■ External storage
There are the following three types of storage used for storage.
Each storage is saved in the following in the structure of Device File Explorer of Android Studio.
To save a file, get an instance of `FileOutputStream``` using the ```openFileOutput ()` method. This will allow you to open the stream. Also, if you use ```openFileOutput () `` `, the path will be automatically acquired and saved even if you do not specify the path of the internal storage.
FileOutputStream fileOutputstream = openFileOutput("text.txt", Context.MODE_PRIVATE);
** First argument **
"/path/file name"
** Second argument **
| value | Description |
|---|---|
| MODE_WORLD_READABLE | Can be referenced from other apps |
| MODE_WORLD_WRITEABLE | Can be written from other apps |
| MODE_PRIVATE | Not accessible from other apps |
| MODE_APPEND | If there is a file, add it |
Also, if you want to specify multiple modes, you can specify multiple modes by connecting pipes.
mode_private | mode_append
After that, convert the character string you want to write to the file to a byte type array and write it to the stream using `write ()`.
fileOutputStream.write(str.getBytes());
To read a file, get an instance of `FileInputStream``` using the ```openFileInput ()` method. This will allow you to open the stream.
FileInputStream fileInputStream = openFileInput("text.txt");
inputstreamreaderReads a byte from the stream and decodes it to the specified character. ItbufferedreaderPut it in and read it line by line. To increase conversion efficiencybufferedreaderInsideinputstreamreaderIt seems good to wrap.
BufferedReader reader = new BufferedReader(new InputStreamReader(fileInputStream, "UTF-8"));
String lineBuffer;
while (true){
lineBuffer = reader.readLine();
if (lineBuffer != null){
text += lineBuffer;
}
else {
break;
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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=".MainActivity">
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="50dp"
android:layout_marginTop="100dp"
android:text="Save File"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="100dp"
android:layout_marginTop="100dp"
android:text="Read File"
app:layout_constraintStart_toEndOf="@+id/button1"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="120dp"
android:text=""
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/editText" />
<EditText
android:id="@+id/editText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="30dp"
android:ems="10"
android:inputType="textPersonName"
android:text="Name"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
MainActivity.java
package com.example.keita.myapplication;
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.TextView;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
public class MainActivity extends AppCompatActivity {
private TextView textView;
private Button button1;
private Button button2;
private EditText editText;
private String fileName = "test.txt";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.textView = findViewById(R.id.textView);
this.editText = findViewById(R.id.editText);
this.button1 = findViewById(R.id.button1);
this.button2 = findViewById(R.id.button2);
this.button1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String text = editText.getText().toString();
saveFile(fileName, text);
}
});
this.button2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String str = readFile(fileName);
textView.setText(str);
}
});
}
private void saveFile(String file, String str){
try {
FileOutputStream fileOutputStream = openFileOutput(file, MODE_PRIVATE | MODE_APPEND);
fileOutputStream.write(str.getBytes());
} catch (IOException e) {
e.printStackTrace();
}
}
private String readFile(String file){
String text = null;
try {
FileInputStream fileInputStream = openFileInput(file);
BufferedReader reader = new BufferedReader(new InputStreamReader(fileInputStream, "UTF-8"));
String lineBuffer;
while (true){
lineBuffer = reader.readLine();
if (lineBuffer != null){
text += lineBuffer;
}
else {
break;
}
}
} catch (IOException e) {
e.printStackTrace();
}
return text;
}
}
Recommended Posts