本地文件存储
作者：互联网
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void operate(View v){
Intent it=null;
switch (v.getId()){
case R.id.share_btn:
it = new Intent(this,ShareActivity.class);
break;
case R.id.external_btn:
it = new Intent(this,ExternalActivity.class);
break;
default:
it = new Intent(this,InternalActivity.class);
break;
}//开启其他活动
startActivity(it);
}
}/*SharePreference 持久化数据的更新 不能用在多进程，Google为多进程提供了一个数据同步互斥方案
，那就是基于Binder实现的ContentProvider
对应的xml文件位置一般都在程序私有目录/data/data/包名/shared_prefs目录下，后缀一定是.xml
、用于存放一些类似登录的配置信息、通过类似键值对的方式存储数据、MODE_PRIVATE常用
该文件也可以被其他activity调用，只要找到对应的文件。
SharedPreferences接口、SharedPreferences.Editor存储信息并提交。
*/
public class ShareActivity extends AppCompatActivity {
private EditText accEdt, pwdEdt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_share);
accEdt = findViewById(R.id.acc_edt);
pwdEdt = findViewById(R.id.pwd_edt);
//SharePreference的读取，每次运行先自动读取
//①获取SharePreference对象(参数1：文件名 参数2：模式)
SharedPreferences share = getSharedPreferences("myshare", MODE_PRIVATE);
//②根据key获取内容(参数1：key 参数2：当对应key不存在时，返回参数2的内容作为默认值)
String accStr = share.getString("account", "");//账户
String pwdStr = share.getString("pwd", "");
//set到控件
accEdt.setText(accStr);
pwdEdt.setText(pwdStr);
findViewById(R.id.login_btn).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//1.获取两个输入框的内容
String account = accEdt.getText().toString();
String pwd = pwdEdt.getText().toString();
//2.验证(admin 123) 对比账户名字和密码
if (account.equals("admin") && pwd.equals("123")) {
//2.1存储信息到SharePreference
//①获取SharePreference对象(参数1：文件名，本身就是xml文件 参数2：模式)
SharedPreferences share = getSharedPreferences("myshare", MODE_PRIVATE);
//②获取Editor对象
SharedPreferences.Editor edt = share.edit();
//③存储信息
edt.putString("account", account);
edt.putString("pwd", pwd);
//④指定提交操作
edt.commit();
Toast.makeText(ShareActivity.this, "登录成功", Toast.LENGTH_SHORT).show();
} else {
//2.2验证失败，提示用户
Toast.makeText(ShareActivity.this, "账号或密码错误", Toast.LENGTH_SHORT).show();
}
}
});
}
}
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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=".ShareActivity">
<TextView
android:id="@+id/textView7"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
android:layout_marginBottom="8dp"
android:text="账号："
android:textSize="18sp"
app:layout_constraintBottom_toTopOf="@+id/guideline3"
app:layout_constraintEnd_toStartOf="@+id/guideline5" />
<EditText
android:id="@+id/acc_edt"
android:layout_width="350dp"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
app:layout_constraintBottom_toTopOf="@+id/guideline3"
app:layout_constraintStart_toStartOf="@+id/guideline5" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
android:layout_marginBottom="8dp"
android:text="密码："
android:textSize="18sp"
app:layout_constraintBottom_toTopOf="@+id/guideline4"
app:layout_constraintEnd_toStartOf="@+id/guideline5" />
<EditText
android:id="@+id/pwd_edt"
android:layout_width="350dp"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:inputType="textPassword"
app:layout_constraintBottom_toTopOf="@+id/guideline4"
app:layout_constraintStart_toStartOf="@+id/guideline5" />
<Button
android:id="@+id/login_btn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="15dp"
android:text="登录"
app:layout_constraintTop_toTopOf="@+id/guideline4" />
<androidx.constraintlayout.widget.Guideline
android:id="@+id/guideline3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_constraintGuide_begin="93dp" />
<androidx.constraintlayout.widget.Guideline
android:id="@+id/guideline4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_constraintGuide_begin="179dp" />
<androidx.constraintlayout.widget.Guideline
android:id="@+id/guideline5"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_begin="88dp" />
</androidx.constraintlayout.widget.ConstraintLayout>/* 外部存储，实现写入和读出，动态权限申请 在Manifest加权限<uses-permission 对于外部存储私有目录的读写，不用获取权限就可以用，file和cache，应用数据和应用缓存所在目录 */
public class ExternalActivity extends AppCompatActivity {
EditText infoEdt;
TextView txt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_external);
infoEdt = findViewById(R.id.info_edt);
txt = findViewById(R.id.textView);
//动态权限
//检查自己是否有写入外部存储权限
int permisson = ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);
if (permisson != PackageManager.PERMISSION_GRANTED) {//没有权限
//动态去申请权限
ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
}
}
//申请权限的时候会触发该方法，通过对比请求码来完成一些事情
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
if (requestCode == 1) {
//做事情
}
}
public void operate(View v) {
//获取路径
String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Download/imooc.txt";
Log.e("TAG", path);
//用来判断内存卡存在
//if(Environment.getExternalStorageState().equals("mounted"))
switch (v.getId()) {
case R.id.save_btn:
//新建文件
File f = new File(path);
try {
if (!f.exists()) {
f.createNewFile();
}
//文件输出流（路径，是否追加）
FileOutputStream fos = new FileOutputStream(path, true);
//获取输入框的内容并以字符串类型
String str = infoEdt.getText().toString();
//以字节流方式写入输出流
fos.write(str.getBytes());
} catch (IOException ioe) {
ioe.printStackTrace();
}
break;
//读取并显示
case R.id.read_btn:
try {
FileInputStream fis = new FileInputStream(path);
byte[] b = new byte[1024];
int len = fis.read(b);
String str2 = new String(b, 0, len);
txt.setText(str2);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
break;
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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=".ExternalActivity">
<EditText
android:id="@+id/info_edt"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginTop="22dp"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
android:gravity="left|top"
android:hint="请输入待存储的内容..."
android:maxLines="12"
android:minLines="12"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/read_btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginTop="8dp"
android:layout_marginBottom="8dp"
android:onClick="operate"
android:text="读取"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toEndOf="@+id/save_btn"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/save_btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginTop="8dp"
android:layout_marginBottom="8dp"
android:onClick="operate"
android:text="保存"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="176dp"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
android:layout_marginBottom="32dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>内部存储 两个文件夹：app和data file和cache
public class InternalActivity extends AppCompatActivity {
EditText edt;
TextView txt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_internal);
edt = findViewById(R.id.editText);
txt = findViewById(R.id.textView);
}
public void operate(View v){
// data/data/包名/files
// getCacheDir() data/data/包名/cache
File f = new File(getFilesDir(),"getFilesDirs.txt");
switch (v.getId()){
case R.id.save_btn:
try {
if (!f.exists()) {
f.createNewFile();
}
FileOutputStream fos = new FileOutputStream(f);
fos.write(edt.getText().toString().getBytes());
fos.close();//多了个close
}catch (IOException e){
e.printStackTrace();
}
break;
case R.id.read_btn:
try {
FileInputStream fis = new FileInputStream(f);
byte[] b = new byte[1024];
int len = fis.read(b);
String str2 = new String(b,0,len);
txt.setText(str2);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
break;
}
}
}
布局文件一样。
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission
android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"
tools:ignore="ProtectedPermissions" />
标签：文件,存储,String,void,public,本地,new,edt,id 来源： https://blog.csdn.net/qq_41596457/article/details/118652811