android 读写文件、列出根目录文件及新版本权限

想列出android 内部存储根目录(内部存储也是sd卡形式)

            File path = Environment.getExternalStorageDirectory();

            File[] files=path.listFiles();
            for(int i=0;i<files.length;i++){
                str1 += files[i].getAbsolutePath()+",";
            }
            textView.setText("bb"+str1);

发现老是提示报错 ，debug 发现eacces，是权限问题

1、先在AndroidManifest.xml 里

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

还加了

<application
    android:allowBackup="true"
    android:requestLegacyExternalStorage="true"

发现还没有用，即使在手机权限里加上还不行

2、加上下面代码好了，新版本需要用下面的方式

 private  final int REQUEST_EXTERNAL_STORAGE = 1;
    private  String[] PERMISSIONS_STORAGE = {
            Manifest.permission.READ_EXTERNAL_STORAGE,
            Manifest.permission.WRITE_EXTERNAL_STORAGE };
    public  void verifyStoragePermissions(Activity activity) {
        // Check if we have write permission
        int permission = ActivityCompat.checkSelfPermission(activity,
                Manifest.permission.WRITE_EXTERNAL_STORAGE);
        if (permission != PackageManager.PERMISSION_GRANTED) {
            // We don't have permission so prompt the user
            ActivityCompat.requestPermissions(activity, PERMISSIONS_STORAGE,
                    REQUEST_EXTERNAL_STORAGE);
        }
    }

然后在

onCreate 里调用

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        verifyStoragePermissions(this);

3、后面处理读写文件也ok了

try {
                File urlFile = new File(str3+"/sd/test.txt");
                Log.e("-----------","111");
                InputStreamReader isr = new InputStreamReader(new FileInputStream(urlFile), "UTF-8");
                BufferedReader br = new BufferedReader(isr);
                Log.e("-----------","112221");
                String str = "";
                String mimeTypeLine = null ;
                while ((mimeTypeLine = br.readLine()) != null) {
                    str = str+mimeTypeLine;
                }
                Log.e("-----------",str);
                textView.setText(str);
            } catch (Exception e) {
                e.printStackTrace();
            }

 4 一个显示目录的 Activity

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        verifyStoragePermissions(this);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView textView = this.findViewById(R.id.tv1);

        //String str =getApplicationContext().getFilesDir().getAbsolutePath();

        String str1 = Environment.getExternalStorageDirectory().getAbsolutePath();

        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){

            File path = Environment.getExternalStorageDirectory();

            File[] files=path.listFiles();
            for(int i=0;i<files.length;i++){
                str1 += files[i].getAbsolutePath()+",";
            }
            textView.setText("bb"+str1);
        }

    }
    private  final int REQUEST_EXTERNAL_STORAGE = 1;
    private  String[] PERMISSIONS_STORAGE = {
            Manifest.permission.READ_EXTERNAL_STORAGE,
            Manifest.permission.WRITE_EXTERNAL_STORAGE };
    public  void verifyStoragePermissions(Activity activity) {
        // Check if we have write permission
        int permission = ActivityCompat.checkSelfPermission(activity,
                Manifest.permission.WRITE_EXTERNAL_STORAGE);
        if (permission != PackageManager.PERMISSION_GRANTED) {
            // We don't have permission so prompt the user
            ActivityCompat.requestPermissions(activity, PERMISSIONS_STORAGE,
                    REQUEST_EXTERNAL_STORAGE);
        }
    }

}