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

==========================================================================================

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" />

第一个页面布局：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="5dp" >
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="40dp" >
<TextView
android:id="@+id/tv_name"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:gravity="center"
android:text="姓名："
android:textColor="@color/black"
android:textSize="17sp" />
<EditText
android:id="@+id/et_name"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginBottom="3dp"
android:layout_marginTop="3dp"
android:layout_toRightOf="@+id/tv_name"
android:background="@drawable/editext_selector"
android:gravity="left|center"
android:hint="请输入姓名"
android:inputType="text"
android:maxLength="12"
android:textColor="@color/black"
android:textSize="17sp" />
RelativeLayout>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="40dp" >
<TextView
android:id="@+id/tv_age"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:gravity="center"
android:text="年龄："
android:textColor="@color/black"
android:textSize="17sp" />
<EditText
android:id="@+id/et_age"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginBottom="3dp"
android:layout_marginTop="3dp"
android:layout_toRightOf="@+id/tv_age"
android:background="@drawable/editext_selector"
android:gravity="left|center"
android:hint="请输入年龄"
android:inputType="number"
android:maxLength="2"
android:textColor="@color/black"
android:textSize="17sp" />
RelativeLayout>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="40dp" >
<TextView
android:id="@+id/tv_height"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:gravity="center"
android:text="身高："
android:textColor="@color/black"
android:textSize="17sp" />
<EditText
android:id="@+id/et_height"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginBottom="3dp"
android:layout_marginTop="3dp"
android:layout_toRightOf="@+id/tv_height"
android:background="@drawable/editext_selector"
android:gravity="left|center"
android:hint="请输入身高"
android:inputType="number"
android:maxLength="3"
android:textColor="@color/black"
android:textSize="17sp" />
RelativeLayout>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="40dp" >
<TextView
android:id="@+id/tv_weight"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:gravity="center"
android:text="体重："
android:textColor="@color/black"
android:textSize="17sp" />
<EditText
android:id="@+id/et_weight"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginBottom="3dp"
android:layout_marginTop="3dp"
android:layout_toRightOf="@+id/tv_weight"
android:background="@drawable/editext_selector"
android:gravity="left|center"
android:hint="请输入体重"
android:inputType="numberDecimal"
android:maxLength="5"
android:textColor="@color/black"
android:textSize="17sp" />
RelativeLayout>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="40dp" >
<CheckBox
android:id="@+id/ck_married"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:gravity="center"
android:checked="false"
android:text="已婚"
android:textColor="@color/black"
android:textSize="17sp" />
RelativeLayout>
<Button
android:id="@+id/btn_save"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="保存文本到存储卡"
android:textColor="@color/black"
android:textSize="17sp" />
<TextView
android:id="@+id/tv_path"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:textColor="@color/black"
android:textSize="17sp" />
LinearLayout>

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 getFileList(String path, String[] extendArray) {
List displayedCOntent= new ArrayList();
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() {
@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 fileExtensiOns= new ArrayList();
for (int i = 0; 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：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="5dp" >
<Button
android:id="@+id/btn_delete"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="删除所有文本文件"
android:textColor="@color/black"
android:textSize="17sp" />
<TextView
android:id="@+id/tv_content"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textColor="@color/black"
android:textSize="17sp" />
LinearLayout>

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 mFilelist = new ArrayList();
@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 ) {
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");
}
}
}