动态请求权限

package com.bwie.dynamicpermissionsapply;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Environment;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;

public class MainActivity extends AppCompatActivity {

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

    public void btnPermissions(View view) {
        getPermissions();

    }

    public void writeScard() {
        try {
            OutputStream os = new FileOutputStream(new File(Environment.getExternalStorageDirectory(), "xx.txt"));

            os.write(("哈哈哈哈哈哈哈").getBytes());
            os.flush();
            os.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void getPermissions() {

        //这句话的意思就是  如果没有获得写入sdcard的权限
        if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.WRITE_EXTERNAL_STORAGE) !=
                PackageManager.PERMISSION_GRANTED ||
                ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) !=
                        PackageManager.PERMISSION_GRANTED) {

            if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) ||
                    ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.READ_EXTERNAL_STORAGE)) {

                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE
                        , Manifest.permission.READ_CALENDAR}, 100);
            } else {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE
                        , Manifest.permission.READ_CALENDAR}, 100);
            }


        } else {
            //如果已经授权  直接读取sdcard的文件就行了

            readSdcard();

        }


    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        if (requestCode == 100) {


            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                System.out.println("写入授权成功");
                writeScard();
            } else if (grantResults.length > 0 && grantResults[1] == PackageManager.PERMISSION_GRANTED) {
                System.out.println("读取授权成功");
                readSdcard();
            } else {
                Toast.makeText(this, "没有得到授权", Toast.LENGTH_SHORT).show();
            }
        }

    }

    public void readSdcard() {
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(new File(Environment.getExternalStorageDirectory(), "xx.txt"))));
            String s = br.readLine();

            Toast.makeText(this, "读取到内容是：" + s, Toast.LENGTH_SHORT).show();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}