在Manifest中也要加入权限，不加也会出问题

SDFile

package com.chuanxidemo.shaoxin.demo06;import android.Manifest;import android.content.pm.PackageManager;import android.os.Bundle;import android.os.Environment;import android.support.annotation.NonNull;import android.support.annotation.Nullable;import android.support.v4.app.ActivityCompat;import android.support.v4.content.ContextCompat;import android.support.v7.app.AppCompatActivity;import android.view.View;import android.widget.Button;import android.widget.Toast;import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;/** * Created by shaoxin on 2017/2/23. */public class SDFile extends AppCompatActivity {    private Button sdread;    private Button sdwrite;    private FileOutputStream outputStream;    private static int REQUEST_EXTERNAL_STRONGE = 1;    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.sdfile);        sdread = (Button) findViewById(R.id.sdread);        sdwrite = (Button) findViewById(R.id.sdwrite);        sdread.setOnClickListener(new MyClick());        sdwrite.setOnClickListener(new MyClick());    }//申请权限的方法包装，与clock 中的if语句的内容作用一样//    public static void verifyStoragePermissions(Activity activity) {////        if (ContextCompat.checkSelfPermission(activity, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {//            ActivityCompat.requestPermissions(activity, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE}, REQUEST_EXTERNAL_STRONGE);//        }//REQUEST_EXTERNAL_STRONGE是自定义个的一个对应码，用来验证请求是否通过//    }    @Override    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {        super.onRequestPermissionsResult(requestCode, permissions, grantResults); //根据请求是否通过的返回码进行判断，然后进一步运行程序        if (grantResults.length > 0 && requestCode == REQUEST_EXTERNAL_STRONGE && grantResults[0] == PackageManager.PERMISSION_GRANTED) {            writerSD();        }    }    public class MyClick implements View.OnClickListener {        @Override        public void onClick(View v) {            switch (v.getId()) {                case R.id.sdwrite:                    //获取SD路径                    //判断是否有SD卡                    if (ContextCompat.checkSelfPermission(SDFile.this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {                        ActivityCompat.requestPermissions(SDFile.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE}, REQUEST_EXTERNAL_STRONGE);                    }//REQUEST_EXTERNAL_STRONGE是自定义个的一个对应码，用来验证请求是否通过                    else {                        writerSD();                    }                    break;                case R.id.sdread:                    break;            }        }    }//封装了数据写入SD卡的方法    public void writerSD() {        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {        } else {            Toast.makeText(SDFile.this, "SD卡不存在", Toast.LENGTH_SHORT).show();        }        File file = Environment.getExternalStorageDirectory();        File newfile = new File(file, "1.txt");        try {            outputStream = new FileOutputStream(file);            outputStream.write("123".getBytes());        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        } finally {            if (outputStream != null) {                try {                    outputStream.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }    }}

sdfile.xml