安卓——数据存储之文件存储

痛定思痛。 2022-05-27 23:35 224阅读 0赞

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遇到的小插曲：找不到创建的文件在哪里怎么办？

看了这篇博客：[https://blog.csdn.net/xdqkid/article/details/53745569][https_blog.csdn.net_xdqkid_article_details_53745569]

原来得在手机中手动设置程序的权限

然后创建的文件并没有在预期的目录下，而是在stroge里

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File类的小试

package com.example.lenovo.filedemo1;
    
    import android.annotation.SuppressLint;
    import android.app.Activity;
    import android.os.Bundle;
    import android.os.Environment;
    import android.util.Log;
    import android.widget.Toast;
    
    import java.io.File;
    import java.io.IOException;
    
    public class MainActivity extends Activity {
    
        @SuppressLint("WrongConstant")
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
           /* File file=new File("/mnt/sdcard/test.txt");
            if(!file.exists()){
                try {
                    file.createNewFile();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }else{
                Toast.makeText(MainActivity.this,"文件已经存在",Toast.LENGTH_SHORT).show();
            }*/
    
           /*
           File file=this.getFilesDir();//当前应用程序默认存储的目录
           Log.i("main",file.toString());
           */
    
           // File file=this.getCacheDir();//当前应用程序默认缓存文件的存储目录
           // Log.i("main",file.toString());
    
            //得到外部的存储位置，该位置的数据跟内置的使用是一样的
            File file=this.getExternalCacheDir();
            Log.i("main",file.toString());

}
    }

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activity\_main.xml

<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout 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="com.example.lenovo.filedemo2.MainActivity">
    
        <EditText
            android:id="@+id/editText1"
            android:layout_width="wrap_content"
            android:layout_height="300dp"
            android:layout_alignParentRight="true"
            android:layout_alignParentLeft="true"
            android:layout_alignParentTop="true"
            android:ems="10"
             />
    
        <Button
            android:id="@+id/write"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/editText1"
            android:layout_centerHorizontal="true"
            android:text="写入并读取出来" />
    
        <TextView
            android:id="@+id/conentValue"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentStart="true"
            android:layout_below="@+id/write"
            android:text="TextView" />
    
    </RelativeLayout>

MainActivity.java

package com.example.lenovo.filedemo2;
    
    import android.app.Activity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.Button;
    import android.widget.EditText;
    import android.widget.TextView;
    
    import java.io.ByteArrayOutputStream;
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.FileOutputStream;
    import java.io.IOException;
    
    public class MainActivity extends Activity {
        EditText editText;
        Button button;
        TextView textView;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            editText=(EditText)findViewById(R.id.editText1);
            button=(Button)findViewById(R.id.write);
            textView=(TextView)findViewById(R.id.conentValue);
    
            button.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    WriteFile(editText.getText().toString());
                    textView.setText(readFiles());
                }
            });
        }
    
        //保存文件
        public void WriteFile(String content){
    
            try {
                //默认写到了/data/data/<包名>.<程序名>/files文件下
                FileOutputStream fileOutputStream=openFileOutput("a.txt",MODE_PRIVATE);//如果文件不存在，默认会自动创建
                fileOutputStream.write(content.getBytes());
                fileOutputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
    
        }
    
        //读取文件内容
        public String readFiles(){
            String content=null;
            FileInputStream fileInputStream;
            ByteArrayOutputStream byteArrayOutputStream;
            try {
                 fileInputStream=openFileInput("a.txt");
                 byteArrayOutputStream=new ByteArrayOutputStream();
                byte [] buffer=new byte[1024];
                int len=0;
                while((len=fileInputStream.read(buffer))!=-1){
                    byteArrayOutputStream.write(buffer,0,len);
                }
                content=byteArrayOutputStream.toString();
                fileInputStream.close();
                byteArrayOutputStream.close();
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return  content;
        }
    }

[70]: /images/20220528/4a239dd5fa77405da15583c001a6b566.png
[70 1]: /images/20220528/054eac7d84d24104a42daaa90b50e2d0.png
[https_blog.csdn.net_xdqkid_article_details_53745569]: https://blog.csdn.net/xdqkid/article/details/53745569
[70 2]: /images/20220528/72f15c2c491540708d53e33da500d02b.png
[70 3]: /images/20220528/bd6c92ce6a8c4a0e812db4a9ea804c95.png
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[70 8]: /images/20220528/edaf669c6cab4f47a946e0d129f1a996.png