在应用中单击打开后，如何使用对话框从下载管理器中打开特定文件

Question

我正在尝试使用对话框中的“打开”按钮来打开特定文件。

这就是我尝试过的Open a file downloaded using download manager Android

package com.conquest.conquestcapital;

import android.Manifest;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.DownloadManager;
import android.content.ActivityNotFoundException;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Build;
import android.os.Environment;
import android.support.v4.app.ActivityCompat;
import android.support.v4.widget.SwipeRefreshLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.KeyEvent;
import android.webkit.DownloadListener;
import android.webkit.URLUtil;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

import java.io.File;



public class MainActivity extends AppCompatActivity
{
    WebView mWebView;

    SwipeRefreshLayout swipe;
    private Activity mActivity;
    private Context mContext;

    private static final int MY_PERMISSION_REQUEST_CODE = 123;



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


        swipe = (SwipeRefreshLayout) findViewById(R.id.swipe);
        swipe.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener()
        {
            public void onRefresh(){
                LoadWeb();
            }
        });

        LoadWeb();

    }

    public void LoadWeb() {
        mContext = getApplicationContext();
        mActivity = MainActivity.this;
        mWebView = (WebView) findViewById(R.id.webView);
        mWebView.getSettings().setJavaScriptEnabled(true);
        mWebView.getSettings().setAppCacheEnabled(true);
        mWebView.setVerticalScrollBarEnabled(true);
        mWebView.setHorizontalScrollBarEnabled(true);
        final String url = "https://www.conquestcapitalltd.com/";
        mWebView.loadUrl(url);
        swipe.setRefreshing(true);
        checkPermission();
        mWebView.setWebViewClient(new WebViewClient() {

            //public void onReveivedError(WebView view, int errorCode, String description, String failingUrl){
            //   mWebView.loadUrl("file://android_asset/error.html");
            //}

            public void onPageFinished(WebView view, String url) {
                //hide the swipe refreshlayout
                swipe.setRefreshing(false);
            }

        });
        mWebView.setDownloadListener(new DownloadListener() {
            @Override
            public void onDownloadStart(String url, String userAgent, String contentDescription,
                                        String mimetype, long contentLength) {
                DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
                request.allowScanningByMediaScanner();
                request.setNotificationVisibility(
                        DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
                final String fileName = URLUtil.guessFileName(url, contentDescription, mimetype);
                if (fileName != null && !TextUtils.isEmpty(fileName)) {
                    File file = new File(Environment.getExternalStorageDirectory().toString() + File.separator + Environment.DIRECTORY_DOWNLOADS, "/" + fileName);
                    if (file.exists()) {
                        AlertDialog.Builder warningMessage = new AlertDialog.Builder(MainActivity.this);
                        warningMessage.setMessage("The file already exists. Click open")
                                .setCancelable(false)
                                .setIcon(android.R.drawable.ic_dialog_alert)
                                .setPositiveButton("open", new DialogInterface.OnClickListener() {
                                    @Override
                                    public void onClick(DialogInterface dialog, int which) {
                                        File file = new File(Environment.getExternalStorageDirectory().toString() + File.separator + Environment.DIRECTORY_DOWNLOADS, "/" + fileName);
                                        Intent intent = new Intent(Intent.ACTION_VIEW);
                                        intent.setDataAndType(Uri.fromFile(file), "capital-company-profile-2016/pdf");
                                        intent.setFlags(Intent.FLAG_ACTIVITY_NO_HISTORY);
                                        try {
                                            startActivity(intent);
                                        } catch (ActivityNotFoundException e) {
                                            Toast.makeText(getApplicationContext(), "File not found", Toast.LENGTH_SHORT).show();

                                        }

                                    }
                                });




                        warningMessage.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int which) {
                                    dialog.cancel();
                                }
                        });
                        warningMessage.show();

                    } else {
                        request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, fileName);

                        DownloadManager dManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
                        dManager.enqueue(request);
                        Toast.makeText(getApplicationContext(), "Downloading File...", Toast.LENGTH_LONG).show();
                        Uri uri = Uri.parse(url);
                        Intent intent = new Intent(Intent.ACTION_VIEW, uri);
                        startActivity(intent);
                    }
                }
            }
        });
    }
    protected void checkPermission () {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
                if (shouldShowRequestPermissionRationale(Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
                    //Alert Dialog
                    AlertDialog.Builder builder = new AlertDialog.Builder(mActivity);
                    builder.setMessage("Write external storage permission is required.");
                    builder.setTitle("Please grant permission");
                    builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialogInterface, int i) {
                            ActivityCompat.requestPermissions(mActivity, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                                    MY_PERMISSION_REQUEST_CODE
                            );
                        }
                    });
                    builder.setNeutralButton("Cancel", null);
                    AlertDialog dialog = builder.create();
                    dialog.show();
                } else {
                    ActivityCompat.requestPermissions(
                            mActivity,
                            new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, MY_PERMISSION_REQUEST_CODE
                    );
                }
            } else {
                //permission already granted
            }

        }
    }


    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode){
            case MY_PERMISSION_REQUEST_CODE:{
                if(grantResults.length>0 && grantResults[0] == PackageManager.PERMISSION_GRANTED){
                }else{
                    //permission denied
                }
            }
        }
    }

    @Override
    public boolean onKeyDown(final int keyCode, final KeyEvent event) {
        if ((keyCode == KeyEvent.KEYCODE_BACK) && mWebView.canGoBack()) {
            mWebView.goBack();
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }
}

我希望当用户从Web视图中按下载时，出现一个对话框，再按一次下载时，会出现一个警告按钮，并且当单击“打开”时，用户可以在应用程序中打开文件。