android小功能实现之文件读写

新建一个Android工程。


一 布局
先看效果图：

打开main.xml修改内容如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <TextView android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/filename" />

    <EditText android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/filename" />

    <TextView android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/file_content" />

    <EditText android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:minLines="3"
        android:id="@+id/save_file_content" />

    <Button android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_save"
        android:id="@+id/button_save"/>

    <Button android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_read"
        android:id="@+id/button_read"/>

    <EditText android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:minLines="3"
        android:id="@+id/read_file_content" />
</LinearLayout>

二 定义字符串
打开strings.xml添加内容如下：

<resources>
    <string name="app_name">File</string>
    <string name="action_settings">Settings</string>


    <string name="filename">文件名称</string>
    <string name="file_content">文件内容</string>
    <string name="button_save">保存</string>
    <string name="save_success">保存成功</string>
    <string name="save_fail">保存失败</string>


    <string name="button_read">读取</string>
    <string name="read_success">读取成功</string>
    <string name="read_fail">读取失败</string>
</resources>

三 功能实现
新建一个类FileService，用于文件的读写，完整代码如下：

public class FileService {
    public Context context;

       public  FileService(Context context){
           this.context = context;
       }

    /**
     * 保存字符串到文件
     * @param name 文件名
     * @param content 文件内容
     */
    public void save(String name, String content) throws Exception{
        // MODE_PRIVATE 创建出来的文件，仅能被本应用访问，而且新写入的内容会覆盖原来的内容
         FileOutputStream os = context.openFileOutput(name, Context.MODE_PRIVATE);
        // 默认保存在/data/data/<package_name>/files目录
        os.write(content.getBytes());
        os.close();
    }

    /***
     * 读取文件内容
     * @param name 文件名
     * @return
     * @throws Exception
     */
    public String read(String name) throws  Exception{
        FileInputStream is = context.openFileInput(name);
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        byte[] buf = new byte[1024];
        int len = 0;
        while( (len = is.read(buf)) != -1){
            os.write(buf,0, len);
        }
        byte[] data = os.toByteArray();
        String content = new String(data);
        return  content;
    }
}

四　测试代码
修改MainActivity.java代码如下：

    public EditText nameText;
    public EditText saveContentText;
    public EditText readContentText;
    public Button button_read;
    public String filename;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        nameText = (EditText)this.findViewById(R.id.filename);
        saveContentText = (EditText)this.findViewById(R.id.save_file_content);
        readContentText = (EditText)this.findViewById(R.id.read_file_content);

        Button button_save = (Button) this.findViewById(R.id.button_save);
        button_save.setOnClickListener(new ButtonSaveClickListener());

        button_read = (Button) this.findViewById(R.id.button_read);
        button_read.setClickable(false);
        button_read.setOnClickListener(new ButtonReadClickListener());
    }

    private final class ButtonSaveClickListener implements View.OnClickListener{
        public void onClick(View v){
            String name = nameText.getText().toString();
            String content = saveContentText.getText().toString();
            FileService service = new FileService(getApplicationContext());
            try {
                filename = name;
                service.save(name, content);
                filename = name;
                button_read.setClickable(true);
                Toast.makeText(getApplicationContext(),R.string.save_success, Toast.LENGTH_LONG).show();
            }catch (Exception e){
                Toast.makeText(getApplicationContext(),R.string.save_fail, Toast.LENGTH_LONG).show();
                e.printStackTrace();
            }
        }
    }

    private final class ButtonReadClickListener implements View.OnClickListener{
        public void onClick(View v){
            FileService service = new FileService(getApplicationContext());
            try {
                String content = service.read(filename);
                readContentText.setText(content);
                Toast.makeText(getApplicationContext(),R.string.read_success, Toast.LENGTH_LONG).show();
            }catch (Exception e){
                Toast.makeText(getApplicationContext(),R.string.read_fail, Toast.LENGTH_LONG).show();
                e.printStackTrace();
            }
        }
    }

运行结果如图：