package com.example.cdcarddemoavtivity;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import java.io.File;
import java.io.FileOutputStream;
import java.util.ArrayList;
import java.util.List;

public class SDCardDemoActivity extends AppCompatActivity implements View.OnClickListener {
    private static final String TAG = "SDCardDemoActivity";
    private Button button;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.avtivity_cd_card);
        button = (Button) this.findViewById(R.id.write_data_button);
        button.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.write_data_button:
                Log.d(TAG, "获取权限");
                Toast.makeText(this, "获取读写权限", Toast.LENGTH_SHORT).show();
                r_w_permission(v);
                break;
        }
    }

    //存文件方法
    public void sd_card() {
        //获取sd卡路径
        File sdCard = Environment.getExternalStorageDirectory();
        Log.d(TAG, "Ext_file_path == " + sdCard);
            try {
                //把数据写到sd卡上
//                File filePath = new File("/storage/emulated/0");
                File file = new File(sdCard, "info.text");
                FileOutputStream fos = new FileOutputStream(file);
                fos.write("11111".getBytes());
                fos.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    //查询是否有读写权限
    private void r_w_permission(View v) {
        List<String> permissionList = new ArrayList<>();
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_CALENDAR) != PackageManager.PERMISSION_GRANTED) {
            //如果不等于说明没有权限。需要申请权限
            //ActivityCompat.requestPermissions 方法 用于申请权限，第二个参数为 所需权限数组，也就是可申请一个，或多个权限。第三个参数为 requestCode 回调的时候使用
            permissionList.add(Manifest.permission.READ_CALENDAR);
        }
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_CALENDAR) != PackageManager.PERMISSION_GRANTED) {
            permissionList.add(Manifest.permission.WRITE_CALENDAR);
        }
        if (!permissionList.isEmpty()) {
            ActivityCompat.requestPermissions(this,
                    permissionList.toArray(new String[permissionList.size()]), 1);
        } else {
            sd_card();
        }
    }

    /**
     * 处理权限要实现 onRequestPermissionsResult 方法，该方法有三个参数
     * <p>
     * requestCode 和申请权限时 requestCode 对应，
     * permissions 申请的权限数组
     * grantResults 申请结果
     *
     * @param requestCode  请求码
     * @param permissions   请求权限
     * @param grantResults  授权结果
     */
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        switch (requestCode) {
            case 1:
                int resultLength = grantResults.length;
                if (resultLength > 0) {
                    for (int grantCode : grantResults) {
                        if (grantCode == PackageManager.PERMISSION_GRANTED) {
                            Toast.makeText(this, "授权成功", Toast.LENGTH_SHORT).show();
                            sd_card();
                        } else {
                            Toast.makeText(this, "授权失败", Toast.LENGTH_SHORT).show();
                        }
                    }
                }
                break;
            default:
                break;
        }
    }
}

一楼说得对

首先是权限声明，在清单文件里进行配置。

然后是如果6.0+的版本，某些权限是需要动态获取的

https://www.sunofbeach.net/a/1192351879502237696

如果是Android10以上的版本

https://developer.android.com/about/versions/10/privacy

以上