使用流进行文件读写 注意：raw里面的文件只能读取，不能修改
文件操作
文件操作的实质：
使用方式：
使用文件系统进行文件操作
使用raw资源文件(raw资源文件夹下文件不会被编译，保持原数据)
使用外部存储设备
ContentProvider：四大组件之一
用于提供外部应用访问本应用数据库的接口
用于访问其他应用程序数据的类代码部分：
part1：
activity_main.xml
<?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="https://schemas.android.com/apk/res/android" xmlns:app="https://schemas.android.com/apk/res-auto" xmlns:tools="https://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity"> <Button android:id="@+id/button" android:layout_width="match_parent" android:layout_height="wrap_content" android:onClick="showFileOperator" android:text="演示文件操作" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" /> <Button android:id="@+id/button7" android:layout_width="match_parent" android:layout_height="wrap_content" android:onClick="showContentProvider" android:text="演示ContentProvider" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toBottomOf="@+id/button" /> </androidx.constraintlayout.widget.ConstraintLayout> 效果图：
raw_demo.txt
activity_file_operator.xml
<?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="https://schemas.android.com/apk/res/android" xmlns:app="https://schemas.android.com/apk/res-auto" xmlns:tools="https://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".FileOperatorActivity"> <EditText android:id="@+id/et_input" android:layout_width="300dp" android:layout_height="50dp" android:layout_marginTop="80dp" android:ems="10" android:hint="请输入" android:inputType="textPersonName" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" /> <TextView android:id="@+id/tv_out" android:layout_width="wrap_content" android:layout_height="50dp" android:layout_marginTop="20dp" app:layout_constraintEnd_toEndOf="@+id/et_input" app:layout_constraintStart_toStartOf="@+id/et_input" app:layout_constraintTop_toBottomOf="@+id/et_input" /> <Button android:id="@+id/button2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="30dp" android:onClick="write" android:text="写入" app:layout_constraintStart_toStartOf="@+id/et_input" app:layout_constraintTop_toBottomOf="@+id/tv_out" /> <Button android:id="@+id/button3" android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="read" android:text="读取" app:layout_constraintEnd_toEndOf="@+id/et_input" app:layout_constraintTop_toTopOf="@+id/button2" /> <Button android:id="@+id/button4" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="30dp" android:onClick="readRaw" android:text="raw文件读取" app:layout_constraintStart_toStartOf="@+id/button2" app:layout_constraintTop_toBottomOf="@+id/button2" /> <Button android:id="@+id/button5" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="30dp" android:onClick="writeExternal" android:text="外部文件写入" app:layout_constraintStart_toStartOf="@+id/button4" app:layout_constraintTop_toBottomOf="@+id/button4" /> <Button android:id="@+id/button6" android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="readExternal" android:text="外部文件读取" app:layout_constraintEnd_toEndOf="@+id/button3" app:layout_constraintTop_toTopOf="@+id/button5" /> </androidx.constraintlayout.widget.ConstraintLayout> 效果图：
FileOperatorActivity.java
import androidx.appcompat.app.AppCompatActivity; import android.os.Bundle; import android.os.Environment; import android.util.Log; import android.view.View; import android.widget.EditText; import android.widget.TextView; import android.widget.Toast; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; public class FileOperatorActivity extends AppCompatActivity { private EditText et_input; private TextView tv_out; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_file_operator); et_input = findViewById(R.id.et_input); tv_out = findViewById(R.id.tv_out); } /** * 演示文件写入 * @param view */ public void write(View view){ String content = et_input.getText().toString(); FileOutputStream out = null; try { out = openFileOutput("demo.txt", MODE_PRIVATE); out.write(content.getBytes()); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (out != null) { try { out.close(); } catch (IOException e) { e.printStackTrace(); } } } } /** * 演示文件读取 * @param view */ public void read(View view){ FileInputStream input = null; try { input = openFileInput("demo.txt"); int i = input.read(); StringBuffer content = new StringBuffer(); while(i != -1) { content.append((char) i); i = input.read(); } tv_out.setText(content.toString()); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (input != null) { try { input.close(); } catch (IOException e) { e.printStackTrace(); } } } } /** * 演示raw文件夹下文件读取 * @param view */ public void readRaw(View view){ InputStream inputStream = getResources().openRawResource(R.raw.raw_demo); try { int i = inputStream.read(); StringBuffer content = new StringBuffer(); while(i != -1) { content.append((char)i); i = inputStream.read(); } tv_out.setText(content.toString()); } catch (IOException e) { e.printStackTrace(); } finally { if (inputStream != null) { try { inputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } } /** * 演示外部文件写入 * @param view */ public void writeExternal(View view) { //获取外部设备状态,判断外部存储设备是否可用 String state = Environment.getExternalStorageState(); if (state.equals(Environment.MEDIA_MOUNTED)) { //就是输入输出流的使用 //获取路径 File file = getExternalFilesDir(null); File demo = new File(file,"demo.txt"); String content = et_input.getText().toString(); FileOutputStream out = null; try { out = new FileOutputStream(demo); out.write(content.getBytes()); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (out != null) { try { out.close(); } catch (IOException e) { e.printStackTrace(); } } } Toast.makeText(this, "写入完成", Toast.LENGTH_SHORT).show(); } } /** * 演示外部文件读取 * @param view */ public void readExternal(View view) { //判断存储设备是否可用 String state = Environment.getExternalStorageState(); if (state.equals(Environment.MEDIA_MOUNTED)) { File file = new File(getExternalFilesDir(null),"demo.txt"); FileInputStream fileInputStream = null; try { fileInputStream = new FileInputStream(file); int i = fileInputStream.read(); StringBuffer content = new StringBuffer(); while(i != -1) { content.append((char)i); i = fileInputStream.read(); } tv_out.setText(content.toString()); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (fileInputStream != null) { try { fileInputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } } } } 效果图：
写入-读取：
RAW文件读取：
外部文件写入-外部文件读取：
part2：
MainAcitivity.java
import androidx.appcompat.app.AppCompatActivity; import android.content.ContentResolver; import android.content.Intent; import android.net.Uri; import android.os.Bundle; import android.view.View; public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } /** * 跳转文件操作演示 * @param view */ public void showFileOperator(View view){ Intent intent = new Intent(this, FileOperatorActivity.class); startActivity(intent); } /** * 演示ContentProvider * @param view */ public void showContentProvider(View view) { /* * * 1.获取ContentResolver * 2.执行操作 * */ ContentResolver resolver = getContentResolver(); Uri uri = Uri.parse("content://com.example.day12.demo"); resolver.delete(uri, null, null); } } AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="https://schemas.android.com/apk/res/android" package="com.example.day12"> <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=".FileOperatorActivity"></activity> <activity android:name=".MainActivity"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <!-- authorities:就是URI name:指向自定义的ContentProvider exported:是否允许外部访问 --> <provider android:authorities="com.example.day12.demo" android:name="com.example.day12.MyContentProvider" android:exported="true"/> </application> </manifest> MyContentProvider.java
import android.content.ContentProvider; import android.content.ContentValues; import android.database.Cursor; import android.net.Uri; import android.util.Log; import androidx.annotation.NonNull; import androidx.annotation.Nullable; public class MyContentProvider extends ContentProvider { /* * https://www.baidu.com/ * https://:协议名称 * www.baidu.com:地址 * 以上两部分组成URI * * ContentProvider就是通过URI进行访问的 * content://xxxxxxxxx * */ /** * 创建时调用，用于初始化必要的数据 * @return */ @Override public boolean onCreate() { Log.i("demo", "onCreate方法被调用了"); return false; } /** * 查询数据库 * @param uri * @param projection * @param selection * @param selectionArgs * @param sortOrder * @return */ @Nullable @Override public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) { return null; } /** * 获取请求类型的 * @param uri * @return */ @Nullable @Override public String getType(@NonNull Uri uri) { return null; } /** * 向数据库插入数据 * @param uri * @param values * @return */ @Nullable @Override public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) { return null; } /** * 从数据库删除数据 * @param uri * @param selection * @param selectionArgs * @return */ @Override public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) { Log.i("demo", "delete方法被调用了"); return 0; } /** * 更新数据库数据 * @param uri * @param values * @param selection * @param selectionArgs * @return */ @Override public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) { return 0; } } 效果图：
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