Android学习 数据存储之_文件存储
正在学习android的数据存储，记录分享如下:
效果图如下
内部存储
CallopenFileOutput()with the name of the file and the operating mode. This returns a FileOutputStream.
Write to the file withwrite().Close the stream withclose().
To read a file from internal storage:
CallopenFileInput()and pass it the name of the file to read. This returns a FileInputStream.
Read bytes from the file with read().Then close the stream with close().
外部
和内部相比 有几点不同
1.查看外部存储设备是否可用，getExternalStorageState()
2.在清单文件中要加上读写外部存储的权限
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
3.指定具体的存储路径，比如用绝对存储路径
File newfile =new File(dir.getAbsolutePath() + "/" + exFileName);
主要代码如下【仅供参考】
public class MainActivity extends ActionBarActivity {
private static final String FILE_NAME = "fileInDome.txt";
private static final String TAG = "com.example.filestorage.MainActivity";
private EditText etInput;
private EditText etContent;
private static boolean isRbIn = true;
private String exFileName = "fileExDome.txt";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
etInput = (EditText) findViewById(R.id.et_files);
etContent = (EditText) findViewById(R.id.et_content);
Button btRead = (Button) findViewById(R.id.bt_read);
Button btWrite = (Button) findViewById(R.id.bt_write);
btRead.setOnClickListener(new btClickListener());
btWrite.setOnClickListener(new btClickListener());
}
private class btClickListener implements OnClickListener {
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.bt_read:
read_files();
break;
case R.id.bt_write:
write_files();
break;
default:
break;
}
}
}
public void read_files() {
if (isRbIn) {
FileInputStream fis = null;
try {
fis = openFileInput(FILE_NAME);
if (fis.available() == 0)
return;
byte[] readBytes = new byte[fis.available()];
while (fis.read(readBytes) != -1)
;
String readContent = new String(readBytes);
etContent.setText(readContent);
Toast.makeText(this, "文件读取成功，文件长度为：" + readContent.length(), 0)
.show();
fis.close();
} catch (Exception e) {
e.printStackTrace();
}
} else {
// 外部存储
FileInputStream fis =null;
Log.i(TAG, "读取外部存储 isExternalStorageWritable");
if (isExternalStorageWritable()) {
File dir = new File("/sdcard/");
Log.i(TAG, "读取外部存储 /sdcard/");
if(dir.exists() && dir.canWrite()){
Log.i(TAG, "读取外部存储");
try {
fis = new FileInputStream(dir.getAbsolutePath() + "/" + exFileName);
if(fis.available() == 0)
return;
Log.i(TAG, "" + fis.available());
byte[] readBytes =new byte[fis.available()];
while(fis.read(readBytes) !=-1)
;
String readContent =new String(readBytes);
etContent.setText(readContent);
Toast.makeText(this,
"从SD卡读取成功，文件长度为：" + readContent.length(), 0).show();
etInput.setText("");
fis.close();
} catch (Exception e) {
e.printStackTrace();
}
}
} else {
Toast.makeText(this, "外部存储不可写", 0).show();
}
}
}
public void write_files() {
if (isRbIn) {
FileOutputStream fos = null;
try {
// 内部存储
fos = openFileOutput(FILE_NAME, MODE_PRIVATE);
String text = etInput.getText().toString();
fos.write(text.getBytes());
Toast.makeText(this, "文件写入成功，文件长度为：" + text.length(), 0).show();
etInput.setText("");
} catch (Exception e) {
e.printStackTrace();
} finally {
if (fos != null) {
try {
fos.flush();
fos.close();
} catch (Exception e2) {
e2.printStackTrace();
}
}
}
} else {
// 外部存储
FileOutputStream fos =null;
Log.i(TAG, "写入外部存储 isExternalStorageWritable");
if (isExternalStorageWritable()) {
File dir = new File("/sdcard/");
Log.i(TAG, "写入外部存储 /sdcard/");
if(dir.exists() && dir.canWrite()){
Log.i(TAG, "写入外部存储");
File newfile =new File(dir.getAbsolutePath() + "/" + exFileName);
try {
fos = new FileOutputStream(newfile);
String text = etInput.getText().toString();
fos.write(text.getBytes());
Toast.makeText(this,
"文件写入SD卡成功，文件长度为：" + text.length(), 0).show();
etInput.setText("");
fos.close();
} catch (Exception e) {
e.printStackTrace();
}
}
} else {
Toast.makeText(this, "外部存储不可写", 0).show();
}
}
}
/* Checks if external storage is available for read and write */
public boolean isExternalStorageWritable() {
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
return true;
}
return false;
}
public void onRadioButtonClicked(View view) {
switch (view.getId()) {
case R.id.rb_in:
Log.i(TAG, "内部存储");
isRbIn = true;
break;
case R.id.rb_ex:
Log.i(TAG, "外部存储");
isRbIn = false;
break;
default:
break;
}
}
}
参考 https://developer.android.com/