我正在开发一个Webview应用程序，最终使文件选择器（从输入文件形式）起作用，但问题是只能起作用一次。

老实说，我真的是Android Studio的新手，最终使这段代码由我自己来实现，机器人，问题是输入文件的WebView文件选择器只能运行一次

希望您能帮我解释一下，要使它生效，我还需要做些什么，这是我的Mainactivity.java

package www.tribbr.tribbr;

import androidx.appcompat.app.AppCompatactivity;
import androidx.core.app.activityCompat;
import androidx.core.content.ContextCompat;
import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.webkit.ValueCallback;
import android.webkit.WebChromeclient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;


public class Mainactivity extends AppCompatactivity {

    private final static int FCR = 1;
    private WebView webView;
    private ValueCallback<Uri> mUM;
    private ValueCallback<Uri[]> mUMA;


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

        if (Build.VERSION.SDK_INT >= 23 && (ContextCompat.checkSelfPermission(this,Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED || ContextCompat.checkSelfPermission(this,Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED)) {
            activityCompat.requestPermissions(Mainactivity.this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE,Manifest.permission.CAMERA},1);
        }
        assert webView != null;

        webView=findViewById(R.id.webviewid);
        webView.setWebViewClient(new WebViewClient());
        webView.setWebViewClient(new MyAppWebViewClient());

        WebSettings WebSettings = webView.getSettings();
        WebSettings.setJavaScriptEnabled(true);
        WebSettings.setallowFileaccess(true);
        webView.getSettings().setSupportzoom(true);
        webView.getSettings().setBuiltInzoomControls(true);
        if (Build.VERSION.SDK_INT >= 21) {
            WebSettings.setMixedContentMode(0);
            webView.setLayerType(View.LAYER_TYPE_HARDWARE,null);
        } else if (Build.VERSION.SDK_INT >= 19) {
            webView.setLayerType(View.LAYER_TYPE_HARDWARE,null);
        } else if (Build.VERSION.SDK_INT < 19) {
            webView.setLayerType(View.LAYER_TYPE_SOFTWARE,null);
        }
        webView.setWebChromeclient(new WebChromeclient(){//For Android 3.0+
            public void openFileChooser(ValueCallback<Uri> uploadMsg) {

                mUM = uploadMsg;
                Intent i = new Intent(Intent.actION_GET_CONTENT);
                i.addCategory(Intent.CATEGORY_OPENABLE);
                i.setType("*/*");
                Mainactivity.this.startactivityForResult(Intent.createChooser(i,"File Chooser"),FCR);
            }

            // For Android 3.0+,above method not supported in some android 3+ versions,in such case we use this
            public void openFileChooser(ValueCallback uploadMsg,String acceptType) {

                mUM = uploadMsg;
                Intent i = new Intent(Intent.actION_GET_CONTENT);
                i.addCategory(Intent.CATEGORY_OPENABLE);
                i.setType("*/*");
                Mainactivity.this.startactivityForResult(
                        Intent.createChooser(i,"File Browser"),FCR);
            }

            //For Android 4.1+
            public void openFileChooser(ValueCallback<Uri> uploadMsg,String acceptType,String capture) {

                mUM = uploadMsg;
                Intent i = new Intent(Intent.actION_GET_CONTENT);
                i.addCategory(Intent.CATEGORY_OPENABLE);
                i.setType("*/*");
                Mainactivity.this.startactivityForResult(Intent.createChooser(i,Mainactivity.FCR);
            }

            //For Android 5.0+
            public boolean onShowFileChooser(
                    WebView webView,ValueCallback<Uri[]> filePathCallback,WebChromeclient.FileChooserParams fileChooserParams) {

                if (mUMA != null) {
                    mUMA.onReceiveValue(null);
                }

                mUMA = filePathCallback;
                // Intent takePictureIntent = new Intent(MediaStore.actION_IMAGE_CAPTURE);


                Intent contentSelectionIntent = new Intent(Intent.actION_GET_CONTENT);
                contentSelectionIntent.addCategory(Intent.CATEGORY_OPENABLE);
                contentSelectionIntent.setType("*/*");
//                Intent[] intentArray;
//
//                if (takePictureIntent != null) {
//                    intentArray = new Intent[]{takePictureIntent};
//                } else {
//                    intentArray = new Intent[0];
//                }

                Intent chooserIntent = new Intent(Intent.actION_CHOOSER);
                chooserIntent.putExtra(Intent.EXTRA_INTENT,contentSelectionIntent);
                // chooserIntent.putExtra(Intent.EXTRA_TITLE,"Image Chooser");
                // chooserIntent.putExtra(Intent.EXTRA_INITIAL_INTENTS,intentArray);
                startactivityForResult(chooserIntent,FCR);

                return true;
            }
        });

        webView.loadUrl("https://tribbr.me/login.php");
    }

    @Override
    public void onBackpressed() {
        if(webView.canGoBack()) {
            webView.goBack();
        } else {
            super.onBackpressed();
        }
    }


}                                                                           

希望此输入文件选择器可以多次工作。...非常感谢：）