数据存储——四种存储方式——存储卡的文件操作——在存储卡上读写文本文件...

叁歲伎倆 2023-09-28 14:31 11阅读 0赞

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添加权限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
        <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
        
        <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />

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第一个页面布局：

第一个页面代码：

package com.example.myapplication;
    
    import android.content.Intent;
    import android.os.Environment;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.text.TextUtils;
    import android.view.View;
    import android.widget.CheckBox;
    import android.widget.CompoundButton;
    import android.widget.EditText;
    import android.widget.TextView;
    
    public class MainActivity extends AppCompatActivity implements View.OnClickListener, CompoundButton.OnCheckedChangeListener
    {
        private EditText et_name;
        private EditText et_age;
        private EditText et_height;
        private EditText et_weight;
        private boolean isMarried = false;
        private String[] typeArray = {"未婚", "已婚"};
        private String mPath; // 私有目录路径
        private TextView tv_path;
    
        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
    
    
            et_name = findViewById(R.id.et_name);
            et_age = findViewById(R.id.et_age);
            et_height = findViewById(R.id.et_height);
            et_weight = findViewById(R.id.et_weight);
            tv_path = findViewById(R.id.tv_path);
            CheckBox ck_married = findViewById(R.id.ck_married);
    
            ck_married.setOnCheckedChangeListener(this);
            findViewById(R.id.btn_save).setOnClickListener(this);
    
            // 获取当前App的私有下载目录
            mPath = getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS).toString() + "/";
        }
    
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            isMarried = isChecked;
        }
    
        @Override
        public void onClick(View v)
        {
            if (v.getId() == R.id.btn_save) {
                String name = et_name.getText().toString();
                String age = et_age.getText().toString();
                String height = et_height.getText().toString();
                String weight = et_weight.getText().toString();
                if (TextUtils.isEmpty(name)) {
                    ToastUtil.show(this, "请先填写姓名");
                    return;
                } else if (TextUtils.isEmpty(age)) {
                    ToastUtil.show(this, "请先填写年龄");
                    return;
                } else if (TextUtils.isEmpty(height)) {
                    ToastUtil.show(this, "请先填写身高");
                    return;
                } else if (TextUtils.isEmpty(weight)) {
                    ToastUtil.show(this, "请先填写体重");
                    return;
                }
                String content = String.format("　姓名：%s\n　年龄：%s\n　身高：%scm\n　体重：%skg\n　婚否：%s\n　注册时间：%s\n",
                        name, age, height, weight, typeArray[isMarried?1:0], DateUtil.getNowDateTime("yyyy-MM-dd HH:mm:ss"));
                String file_path = mPath + DateUtil.getNowDateTime("") + ".txt";
                FileUtil.saveText(file_path, content); // 把字符串内容保存为文本文件
                tv_path.setText("用户注册信息文件的保存路径为：\n" + file_path);
                ToastUtil.show(this, "数据已写入存储卡文件");
            }
    
            startActivity(new Intent(this,MainActivity2.class));
    
        }
    
    }

工具类：

package com.example.myapplication;
    
    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileOutputStream;
    import java.io.FilenameFilter;
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Comparator;
    import java.util.List;
    import java.util.Locale;
    
    public class FileUtil {
    
        // 把字符串保存到指定路径的文本文件
        public static void saveText(String path, String txt) {
            // 根据指定的文件路径构建文件输出流对象
            try (FileOutputStream fos = new FileOutputStream(path)) {
                fos.write(txt.getBytes()); // 把字符串写入文件输出流
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    
        // 从指定路径的文本文件中读取内容字符串
        public static String openText(String path) {
            String readStr = "";
            // 根据指定的文件路径构建文件输入流对象
            try (FileInputStream fis = new FileInputStream(path)) {
                byte[] b = new byte[fis.available()];
                fis.read(b); // 从文件输入流读取字节数组
                readStr = new String(b); // 把字节数组转换为字符串
            } catch (Exception e) {
                e.printStackTrace();
            }
            return readStr; // 返回文本文件中的文本字符串
        }
    
        // 把位图数据保存到指定路径的图片文件
        public static void saveImage(String path, Bitmap bitmap) {
            // 根据指定的文件路径构建文件输出流对象
            try (FileOutputStream fos = new FileOutputStream(path)) {
                // 把位图数据压缩到文件输出流中
                bitmap.compress(Bitmap.CompressFormat.JPEG, 80, fos);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    
        // 从指定路径的图片文件中读取位图数据
        public static Bitmap openImage(String path) {
            Bitmap bitmap = null; // 声明一个位图对象
            // 根据指定的文件路径构建文件输入流对象
            try (FileInputStream fis = new FileInputStream(path)) {
                bitmap = BitmapFactory.decodeStream(fis); // 从文件输入流中解码位图数据
            } catch (Exception e) {
                e.printStackTrace();
            }
            return bitmap; // 返回图片文件中的位图数据
        }
    
        public static List<File> getFileList(String path, String[] extendArray) {
            List<File> displayedContent = new ArrayList<File>();
            File[] files = null;
            File directory = new File(path);
            if (extendArray != null && extendArray.length > 0) {
                FilenameFilter fileFilter = getTypeFilter(extendArray);
                files = directory.listFiles(fileFilter);
            } else {
                files = directory.listFiles();
            }
    
            if (files != null) {
                for (File f : files) {
                    if (!f.isDirectory() && !f.isHidden()) {
                        displayedContent.add(f);
                    }
                }
            }
            // 按照最后修改时间排序
            Collections.sort(displayedContent, new Comparator<File>() {
                @Override
                public int compare(File o1, File o2) {
                    return (o1.lastModified() > o2.lastModified()) ? -1 : 1;
                }
            });
            return displayedContent;
        }
    
        public static FilenameFilter getTypeFilter(String[] extendArray) {
            final ArrayList<String> fileExtensions = new ArrayList<String>();
            for (int i = 0; i < extendArray.length; i++) {
                fileExtensions.add(extendArray[i]);
            }
            FilenameFilter fileNameFilter = new FilenameFilter() {
                @Override
                public boolean accept(File directory, String fileName) {
                    boolean matched = false;
                    File f = new File(String.format("%s/%s",
                            directory.getAbsolutePath(), fileName));
                    matched = f.isDirectory();
                    if (!matched) {
                        for (String s : fileExtensions) {
                            s = String.format(".{0,}\\%s$", s);
                            s = s.toUpperCase(Locale.getDefault());
                            fileName = fileName.toUpperCase(Locale.getDefault());
                            matched = fileName.matches(s);
                            if (matched) {
                                break;
                            }
                        }
                    }
                    return matched;
                }
            };
            return fileNameFilter;
        }
    
    }

package com.example.myapplication;
    
    import android.content.Context;
    import android.widget.Toast;
    
    public class ToastUtil
    {
    
        public static void show(Context ctx, String desc)
        {
            Toast.makeText(ctx, desc, Toast.LENGTH_SHORT).show();
        }
    }

第二个页面布局：

第二个页面代码：

package com.example.myapplication;
    
    import android.os.Environment;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.View;
    import android.widget.TextView;
    
    import java.io.File;
    import java.util.ArrayList;
    import java.util.List;
    
    
    public class MainActivity2 extends AppCompatActivity implements View.OnClickListener
    {
    
        private final static String TAG = "FileReadActivity";
        private TextView tv_content;
        private String mPath; // 私有目录路径
        private List<File> mFilelist = new ArrayList<File>();
    
        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main2);
    
    
            tv_content = findViewById(R.id.tv_content);
            findViewById(R.id.btn_delete).setOnClickListener(this);
            // 获取当前App的私有下载目录
            mPath = getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS).toString() + "/";
            showFileContent(); // 显示最新的文本文件内容
        }
    
        // 显示最新的文本文件内容
        private void showFileContent() {
            // 获得指定目录下面的所有文本文件
            mFilelist = FileUtil.getFileList(mPath, new String[]{".txt"});
            if (mFilelist.size() > 0) {
                // 打开并显示选中的文本文件内容
                String file_path = mFilelist.get(0).getAbsolutePath();
                String content = FileUtil.openText(file_path);
                String desc = String.format("找到最新的文本文件，路径为%s，内容如下：\n%s",
                        file_path, content);
                tv_content.setText(desc);
            } else {
                tv_content.setText("私有目录下未找到任何文本文件");
            }
        }
    
        @Override
        public void onClick(View v) {
            if (v.getId() == R.id.btn_delete) {
                for (int i = 0; i < mFilelist.size(); i++) {
                    String file_path = mFilelist.get(i).getAbsolutePath();
                    File f = new File(file_path);
                    if (!f.delete()) {
                        Log.d(TAG, "file_path=" + file_path + ", delete failed");
                    }
                }
                ToastUtil.show(this, "已删除私有目录下的所有文本文件");
            }
        }
    
    }

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