Android开发学习笔记整理（13）-文件操作和ContentProvider

文件操作

文件操作的实质：

使用流进行文件读写

使用方式：

• (1) 使用文件系统
• (2) 使用raw资源文件
• (3) 使用外部存储设备

使用文件系统进行文件操作

• (1) 获取输入(openFileInput) / 输出流(openFileOutput)
• (2) 进行文件读/写
• (3) 关闭输入/输出流

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)

• (1) 获取输入
• (2) 进行文件读
• (3) 关闭输入

注意：raw里面的文件只能读取，不能修改

使用外部存储设备

• (1) 获取外部存储设备的状态
• (2) 创建输入输出流进行读写
• (3) 关闭流

ContentProvider：四大组件之一

• URI：https://www. baidu. com/
• 什么是ContentProvider？
  用于提供外部应用访问本应用数据库的接口
• 自定义ContentProvider
• 什么是ContentResoIver？
  用于访问其他应用程序数据的类
• 使用ContentResoIver
• UriMatcher

代码部分：

part1：

activity_main.xml

<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=".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

<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=".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

<manifest xmlns:android="http://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>

        
        <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：