android 6.0 写入SD卡的权限申请实例讲解

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package com.example.admin.sdapplication;

import android.Manifest;
import android.app.Dialog;
import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.os.Build;
import android.os.Bundle;
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.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;

public class SdkActivity extends AppCompatActivity implements View.OnClickListener{
 private Button btn_write;
 private Button btn_read;
 final int REQUEST_WRITE=1;//申请权限的请求码
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_sdk);

  btn_write= (Button) findViewById(R.id.btn_write);
  btn_read= (Button) findViewById(R.id.btn_read);
  btn_read.setOnClickListener(this);
  btn_write.setOnClickListener(this);
 }

 private void showAlert(){
  Dialog alertDialog = new AlertDialog.Builder(this).
    setTitle("权限说明").
    setMessage("我们需要这个权限给你提供存储服务").
    setIcon(R.drawable.ic_launcher).
    setPositiveButton("确定", new DialogInterface.OnClickListener() {

     @Override
     public void onClick(DialogInterface dialog, int which) {
      // TODO Auto-generated method stub
      //2、申请权限: 参数二：权限的数组；参数三：请求码
      ActivityCompat.requestPermissions(SdkActivity.this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},REQUEST_WRITE);
     }
    }).
    setNegativeButton("取消", new DialogInterface.OnClickListener() {

     @Override
     public void onClick(DialogInterface dialog, int which) {
      // TODO Auto-generated method stub
     }
    }).
    create();
  alertDialog.show();
 }
 @Override
 public void onClick(View view) {
  switch (view.getId()){
   case R.id.btn_read:
    String s= readToSdCard();
    Log.i("readTosdCard",s);
    break;
   case R.id.btn_write:
    //判断是否6.0以上的手机 不是就不用
    if(Build.VERSION.SDK_INT>=23){
     //判断是否有这个权限
     if(ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)!=PackageManager.PERMISSION_GRANTED){
      //第一请求权限被取消显示的判断，一般可以不写
      if (ActivityCompat.shouldShowRequestPermissionRationale(SdkActivity.this,
        Manifest.permission.WRITE_EXTERNAL_STORAGE)){
       Log.i("readTosdCard","我们需要这个权限给你提供存储服务");
       showAlert();
      }else {
       //2、申请权限: 参数二：权限的数组；参数三：请求码
       ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},REQUEST_WRITE);
      }
     }else {
      writeToSdCard();
     }
    } else{
     writeToSdCard();
    }
    break;
  }
 }

 //写数据
 public void writeToSdCard(){
  //1、判断sd卡是否可用
  if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
   //sd卡可用
   //2、获取sd卡路径
   File sdFile=Environment.getExternalStorageDirectory();
   File path=new File(sdFile,"a.txt");//sd卡下面的a.txt文件 参数 前面 是目录 后面是文件
   try {
    FileOutputStream fileOutputStream=new FileOutputStream(path);
    fileOutputStream.write("hello".getBytes());
   } catch (Exception e) {
    e.printStackTrace();
   }
  }
 }
 //读数据
 public String readToSdCard(){
  StringBuilder stringBuilder = null;
  if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
   File sdFile=Environment.getExternalStorageDirectory();
   File path=new File(sdFile,"a.txt");
   stringBuilder =new StringBuilder();
   try {
    FileInputStream fileInputStream=new FileInputStream(path);
    BufferedReader bufferedReader=new BufferedReader(new InputStreamReader(fileInputStream));

    String str;
    while ((str=bufferedReader.readLine())!=null){
     stringBuilder.append(str);
    }
   } catch (Exception e) {
    e.printStackTrace();
   }
  }
  return stringBuilder.toString();
 }
 //判断授权的方法 授权成功直接调用写入方法 这是监听的回调
 //参数 上下文 授权结果的数组 申请授权的数组
 @Override
 public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
  super.onRequestPermissionsResult(requestCode, permissions, grantResults);
  if(requestCode==REQUEST_WRITE&&grantResults[0]== PackageManager.PERMISSION_GRANTED){
   writeToSdCard();
  }

 }
}

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//第一请求权限被取消显示的判断，一般可以不写
if (ActivityCompat.shouldShowRequestPermissionRationale(SdkActivity.this,
  Manifest.permission.WRITE_EXTERNAL_STORAGE)){
 Log.i("readTosdCard","我们需要这个权限给你提供存储服务");
 showAlert();
}else {
 //2、申请权限: 参数二：权限的数组；参数三：请求码
 ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},REQUEST_WRITE);
}