android - 从 USB 可移动存储读取文件

Question

在我的应用程序中，我想从 usb 可移动存储中读取一个文件我有一个.txt，我想阅读它

void read() {
UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();
StringBuffer sb = new StringBuffer();
while (deviceIterator.hasNext()) {
    UsbDevice device = deviceIterator.next();
    String Model = device.getDeviceName();

    try {
        File file = new File(Model + "/a.txt");
        if (file.exists())
            Toast.makeText(getApplicationContext(), "Exist", Toast.LENGTH_LONG).show();
        else
            Toast.makeText(getApplicationContext(), "Not Exist", Toast.LENGTH_LONG).show();

        BufferedReader br = new BufferedReader(new FileReader(Model + "/a.txt"));
        String sCurrentLine;

        while ((sCurrentLine = br.readLine()) != null) {
            textView.append(sCurrentLine + "\n");
        }

    } catch (Exception e) {
        e.printStackTrace();
        Toast.makeText(getApplicationContext(), e.toString(), Toast.LENGTH_LONG).show();
    }
}
}

检查文件存在时返回false，打开读取文件时抛出异常

java.io.filenotfoundexception :/dev/bus/001/002/a.txt: 打开失败:EACCES(权限被拒绝)

在Manifest中有

<uses-permission android:name="android.permission.USB_PERMISSION" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_MEDIA_STORAGE" />

Answer 1

如果您在 Lollipop 之上或之上运行，您需要在 Java 代码中请求权限。查看此链接 https://stackoverflow.com/a/33162451/7457753