解决Android7.0更新后无法安装的问题

 if (!apkfile.exists()) {
      Toast.makeText(mContext, "下载的安装包不存在", Toast.LENGTH_SHORT).show();
      return;
    }
 Intent install = new Intent(Intent.ACTION_VIEW);
      install.setDataAndType(Uri.fromFile(apkfile), "application/vnd.android.package-archive");
      install.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
      mContext.startActivity(install);

 if (!apkfile.exists()) {
      Toast.makeText(mContext, "下载的安装包不存在", Toast.LENGTH_SHORT).show();
      return;
    }
    //判读版本是否在7.0以上
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
      //在AndroidManifest中的android:authorities值
      Uri apkUri = FileProvider.getUriForFile(mContext,
          "你的包名.provider", apkfile);
      Intent install = new Intent(Intent.ACTION_VIEW);
      install.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
      //添加这一句表示对目标应用临时授权该Uri所代表的文件
      install.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
      install.setDataAndType(apkUri, "application/vnd.android.package-archive");
      mContext.startActivity(install);
    } else {
      Intent install = new Intent(Intent.ACTION_VIEW);
      install.setDataAndType(Uri.fromFile(apkfile), "application/vnd.android.package-archive");
      install.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
      mContext.startActivity(install);
    }

 <provider
      android:name=".service.MyFileProvider"
      android:authorities="你的包名.provider"
      android:exported="false"
      android:grantUriPermissions="true">
      <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths" />
    </provider>

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <paths>
    <external-path path="" name="download"/>
  </paths>
</resources>

 if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
      //TODO 更新
    } else {
      if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
          == PackageManager.PERMISSION_GRANTED) {
        //TODO 更新 
      } else {//申请权限
        ActivityCompat.requestPermissions(this,
            new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
      }
    }
//权限请求结果
  @Override
  public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);

    switch (requestCode) {
      case 1:
        if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
          //TODO 更新 
        } else {
         Toast.makeText(this, "暂无读写SD卡权限", Toast.LENGTH_SHORT).show();
        }
        break;
    }

  }