java - Android 模拟器应用程序打开时显示空白屏幕

Question

我有一个正在运行的应用程序，但我想实现推送通知，因此必须更新 android studio 并放入产生错误的 firebase 依赖项，因此必须移动到 androidx 并将依赖项包更改为 androidx 包，这些更改解决了问题但是当我启动应用程序时，我看到一个空白的白色屏幕。下面是我的 MainActivity.java 文件中的代码。

package com.example.goldfish;

import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import androidx.appcompat.app.AppCompatActivity;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.os.Parcelable;
import android.provider.MediaStore;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.webkit.ValueCallback;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;
import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import android.widget.ProgressBar;
//import androidx.swiperefreshlayout.widget.SwipeRefreshLayout;

public class MainActivity extends AppCompatActivity{
    private static final int INPUT_FILE_REQUEST_CODE = 1;
    private static final int FILECHOOSER_RESULTCODE = 1;
    private static final String TAG = MainActivity.class.getSimpleName();
    private WebView webView;
    private ValueCallback<Uri> mUploadMessage;
    private Uri mCapturedImageURI = null;
    private ValueCallback<Uri[]> mFilePathCallback;
    private String mCameraPhotoPath;

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            if (requestCode != INPUT_FILE_REQUEST_CODE || mFilePathCallback == null) {
                super.onActivityResult(requestCode, resultCode, data);
                return;
            }
            Uri[] results = null;
            // Check that the response is a good one
            if (resultCode == Activity.RESULT_OK) {
                if (data == null) {
                    // If there is not data, then we may have taken a photo
                    if (mCameraPhotoPath != null) {
                        results = new Uri[]{Uri.parse(mCameraPhotoPath)};
                    }
                } else {
                    String dataString = data.getDataString();
                    if (dataString != null) {
                        results = new Uri[]{Uri.parse(dataString)};
                    }
                }
            }
            mFilePathCallback.onReceiveValue(results);
            mFilePathCallback = null;
        } else if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.KITKAT) {
            if (requestCode != FILECHOOSER_RESULTCODE || mUploadMessage == null) {
                super.onActivityResult(requestCode, resultCode, data);
                return;
            }
            if (requestCode == FILECHOOSER_RESULTCODE) {
                if (null == this.mUploadMessage) {
                    return;
                }
                Uri result = null;
                try {
                    if (resultCode != RESULT_OK) {
                        result = null;
                    } else {
                        // retrieve from the private variable if the intent is null
                        result = data == null ? mCapturedImageURI : data.getData();
                    }
                } catch (Exception e) {
                    Toast.makeText(getApplicationContext(), "activity :" + e,
                            Toast.LENGTH_LONG).show();
                }
                mUploadMessage.onReceiveValue(result);
                mUploadMessage = null;
            }
        }
        return;
    }
   // @Override
  /*  protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mSwipeRefreshLayout= (SwipeRefreshLayout) findViewById(R.id.swipe);
        mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                LoadWeb();
            }
        });
        LoadWeb();
    }
   protected void onCreate(Bundle savedInstanceState) {
        setContentView(R.layout.activity_main);
        mSwipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.container);
        mSwipeRefreshLayout.setOnRefreshListener(this);

        super.onCreate(savedInstanceState);
    }

    @Override
    public void onRefresh() {
        Toast.makeText(this, "Refresh", Toast.LENGTH_SHORT).show();
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                mSwipeRefreshLayout.setRefreshing(false);
            }
        }, 2000);
    }
*/
    public void LoadWeb(){
        webView = (WebView) findViewById(R.id.activity_main_webview);
        //private SwipeRefreshLayout mSwipeRefreshLayout;
        WebSettings webSettings = webView.getSettings();
        webView.loadUrl("https://google.com/"); //change with your website
       // swipe.setRefreshing(true);

        //code from youtube for performance
        webSettings.setJavaScriptEnabled(true);
        webSettings.setLoadWithOverviewMode(true);
        webSettings.setUseWideViewPort(true);
        webSettings.setSupportZoom(true);
        webView.getSettings().setBuiltInZoomControls(false);
        webView.getSettings().setDisplayZoomControls(false);
        webSettings.setLayoutAlgorithm(WebSettings.LayoutAlgorithm.NARROW_COLUMNS);
        webView.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);
        webSettings.setDomStorageEnabled(true);
        webView.setScrollBarStyle(WebView.SCROLLBARS_OUTSIDE_OVERLAY);
        webView.setScrollbarFadingEnabled(true);
        webView.getSettings().setRenderPriority(WebSettings.RenderPriority.HIGH);
        webView.getSettings().setAppCacheEnabled(true);

        webSettings.setSavePassword(true);
        webSettings.setSaveFormData(true);
        webSettings.setEnableSmoothTransition(true);
        if (Build.VERSION.SDK_INT >= 19) {
            webView.setLayerType(View.LAYER_TYPE_HARDWARE, null);
        }
        else if(Build.VERSION.SDK_INT >=11 && Build.VERSION.SDK_INT < 19) {
            webView.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        }
        //end of performance improvement code
        webSettings.setLoadWithOverviewMode(true);
        webSettings.setAllowFileAccess(true);
        webView.setWebViewClient(new Client());
        webView.setWebChromeClient(new ChromeClient());
        int Permission_All = 1;
        String[] Permissions = {Manifest.permission.MEDIA_CONTENT_CONTROL, Manifest.permission.CAMERA};
        if (!hasPermissions(this, Permissions)) {
            ActivityCompat.requestPermissions(this, Permissions, Permission_All);
        }
    }

    private File createImageFile() throws IOException {
        // Create an image file name
        String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
        String imageFileName = "JPEG_" + timeStamp + "_";
        File storageDir = Environment.getExternalStoragePublicDirectory(
                Environment.DIRECTORY_PICTURES);
        File imageFile = File.createTempFile(
                imageFileName,  /* prefix */
                ".jpg",         /* suffix */
                storageDir      /* directory */
        );
        return imageFile;
    }


    public class ChromeClient extends WebChromeClient {
        // For Android 5.0
        public boolean onShowFileChooser(WebView view, ValueCallback<Uri[]> filePath, WebChromeClient.FileChooserParams fileChooserParams) {
            // Double check that we don't have any existing callbacks
            if (mFilePathCallback != null) {
                mFilePathCallback.onReceiveValue(null);
            }
            mFilePathCallback = filePath;
            Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
            if (takePictureIntent.resolveActivity(getPackageManager()) != null) {
                // Create the File where the photo should go
                File photoFile = null;
                try {
                    photoFile = createImageFile();
                    takePictureIntent.putExtra("PhotoPath", mCameraPhotoPath);
                } catch (IOException ex) {
                    // Error occurred while creating the File
                    Log.e(TAG, "Unable to create Image File", ex);
                }
                // Continue only if the File was successfully created
                if (photoFile != null) {
                    mCameraPhotoPath = "file:" + photoFile.getAbsolutePath();
                    takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT,
                            Uri.fromFile(photoFile));
                } else {
                    takePictureIntent = null;
                }
            }
            Intent contentSelectionIntent = new Intent(Intent.ACTION_GET_CONTENT);
            contentSelectionIntent.addCategory(Intent.CATEGORY_OPENABLE);
            contentSelectionIntent.setType("image/*");
            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, INPUT_FILE_REQUEST_CODE);
            return true;
        }




        // openFileChooser for Android 3.0+
        public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType) {
            mUploadMessage = uploadMsg;
            // Create AndroidExampleFolder at sdcard
            // Create AndroidExampleFolder at sdcard
            File imageStorageDir = new File(
                    Environment.getExternalStoragePublicDirectory(
                            Environment.DIRECTORY_PICTURES)
                    , "AndroidExampleFolder");
            if (!imageStorageDir.exists()) {
                // Create AndroidExampleFolder at sdcard
                imageStorageDir.mkdirs();
            }
            // Create camera captured image file path and name
            File file = new File(
                    imageStorageDir + File.separator + "IMG_"
                            + String.valueOf(System.currentTimeMillis())
                            + ".jpg");
            mCapturedImageURI = Uri.fromFile(file);
            // Camera capture image intent
            final Intent captureIntent = new Intent(
                    android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
            captureIntent.putExtra(MediaStore.EXTRA_OUTPUT, mCapturedImageURI);
            Intent i = new Intent(Intent.ACTION_GET_CONTENT);
            i.addCategory(Intent.CATEGORY_OPENABLE);
            i.setType("image/*");
            // Create file chooser intent
            Intent chooserIntent = Intent.createChooser(i, "Image Chooser");
            // Set camera intent to file chooser
            chooserIntent.putExtra(Intent.EXTRA_INITIAL_INTENTS
                    , new Parcelable[] { captureIntent });
            // On select image call onActivityResult method of activity
            startActivityForResult(chooserIntent, FILECHOOSER_RESULTCODE);
        }
        // openFileChooser for Android < 3.0
        public void openFileChooser(ValueCallback<Uri> uploadMsg) {
            openFileChooser(uploadMsg, "");
        }
        //openFileChooser for other Android versions
        public void openFileChooser(ValueCallback<Uri> uploadMsg,
                                    String acceptType,
                                    String capture) {
            openFileChooser(uploadMsg, acceptType);
        }
    }

    public boolean onKeyDown(int keyCode, KeyEvent event) {
        // Check if the key event was the Back button and if there's history
        if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) {
            webView.goBack();
            return true;
        }
        // If it wasn't the Back key or there's no web page history, bubble up to the default
        // system behavior (probably exit the activity)
        return super.onKeyDown(keyCode, event);
    }

    public class Client extends WebViewClient {
        ProgressDialog progressDialog;

        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            // If url contains mailto link then open Mail Intent
            if (url.contains("mailto:")) {
                // Could be cleverer and use a regex
                //Open links in new browser
                view.getContext().startActivity(
                        new Intent(Intent.ACTION_VIEW, Uri.parse(url)));
                // Here we can open new activity
                return true;
            }else {
                // Stay within this webview and load url
                view.loadUrl(url);
                return true;
            }
        }

        //Show loader on url load
        public void onPageStarted(WebView view, String url, Bitmap favicon) {
            // Then show progress  Dialog
            // in standard case YourActivity.this
//            if (progressDialog == null) {
//                progressDialog = new ProgressDialog(MainActivity.this);
//                progressDialog.setMessage("Loading...");
//                progressDialog.show();
//            }
//            view.setVisibility(webView.INVISIBLE);
        }

        // Called when all page resources loaded
        public void onPageFinished(WebView view, String url) {
            try {
                // Close progressDialog
//                if (progressDialog.isShowing()) {
//                    progressDialog.dismiss();
//                    progressDialog = null;
//                }
//                spinner.setVisibility(View.GONE);
//
//                view.setVisibility(webView.VISIBLE);
//                super.onPageFinished(view, url);
             //   swipe.setRefreshing(false);
                if (findViewById(R.id.splach_screen).getVisibility() == View.VISIBLE) {
// show webview
                    findViewById(R.id.swipe).setVisibility(View.VISIBLE);
// hide splash screen
                    findViewById(R.id.splach_screen).setVisibility(View.GONE);
                }
            } catch (Exception exception) {
                exception.printStackTrace();
            }
        }

    }

    //User Media Permission....as_060319
    public  static boolean hasPermissions (Context context, String... permissions){
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && context != null && permissions != null) {
            for(String permission: permissions) {
                if (ActivityCompat.checkSelfPermission(context, permission) != PackageManager.PERMISSION_GRANTED) {
                    return false;
                }
            }
        }
            return true;
    }
}

任何帮助或见解将非常感激。

Answer 1

根据android的生命周期首先调用 Oncreate，我们使用 setcontentview(R.layout.activity_main) 来设置 contentview 和布局，但似乎您已经注释掉了 oncreate 方法。