Android Studio App 在模拟器中不断崩溃

Question

我正在开发一个 Android 应用程序，有一天它在模拟器中不断崩溃。 幸运的是，我在 github 上拥有一切，并在一个单独的分支上工作。 所以我以为我只是 go 一个月后我新的它工作了 100%，但这并没有帮助。 我的应用程序在模拟器内启动时仍然崩溃。

调试：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: ch.xxx.xxx, PID: 8013
java.lang.RuntimeException: Unable to start activity ComponentInfo{ch.xxx.xxx/ch.xxx.xxx.SecondActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.webkit.WebSettings android.webkit.WebView.getSettings()' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:223)
    at android.app.ActivityThread.main(ActivityThread.java:7656)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.webkit.WebSettings android.webkit.WebView.getSettings()' on a null object reference
    at ch.xxx.xxx.SecondActivity.StartWebView(SecondActivity.java:88)
    at ch.xxx.xxx.SecondActivity.CheckInternetState(SecondActivity.java:81)
    at ch.xxx.xxx.SecondActivity.onCreate(SecondActivity.java:51)
    at android.app.Activity.performCreate(Activity.java:8000)
    at android.app.Activity.performCreate(Activity.java:7984)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:223) 
    at android.app.ActivityThread.main(ActivityThread.java:7656) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

我做了一些研究，但没有找到任何东西。 如果信息太少，请写下您需要的评论。

编辑：

XML：

<?xml version="1.0" encoding="utf-8"?>

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.CAMERA2" />
<uses-permission android:name="android.permission.WRITE_INTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_INTERNAL_STORAGE" />
<uses-feature android:name="android.hardware.camera"
    android:required="false" />
<application
    android:allowBackup="true"
    android:hardwareAccelerated="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/Theme.DOCDevices"
    android:usesCleartextTraffic="true">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".noconnectionActivity" />
    <activity android:name=".SecondActivity" />
</application>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
android:background="#000000">

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#000000"
    android:visibility="visible">

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:layout_marginStart="150dp"
        android:layout_marginLeft="150dp"
        android:alpha="1"
        android:scaleType="centerInside"
        android:src="@drawable/blue_1"
        android:visibility="visible"></ImageView>
</RelativeLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

主视图.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#000000"
tools:context=".SecondActivity">

<WebView
    android:id="@+id/webView"
    style="@android:style/Widget.DeviceDefault.WebView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#000000"
    android:visibility="visible"></WebView>

</androidx.constraintlayout.widget.ConstraintLayout>

主要活动：

package ch.xxx.xxx;

import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.view.WindowManager;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

private static int SPLASH_SCREEN_TIME_OUT=2000;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
    //This method is used so that your splash activity
    //can cover the entire screen.

    setContentView(R.layout.activity_main);
    //this will bind your MainActivity.class file with activity_main.

    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            Intent i=new Intent(MainActivity.this,
                    SecondActivity.class);
            //Intent is used to switch from one activity to another.

            startActivity(i);
            //invoke the SecondActivity.

            finish();
            //the current activity will get finished.
        }
    }, SPLASH_SCREEN_TIME_OUT);

}

}

第二个活动：

package ch.xxx.xxx;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.ActivityNotFoundException;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.ConnectivityManager;
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.webkit.ValueCallback;
import android.webkit.WebChromeClient;
import android.webkit.WebResourceError;
import android.webkit.WebResourceRequest;
import android.webkit.WebView;
import android.widget.ImageView;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

public class SecondActivity extends AppCompatActivity {
public WebView webView;
ImageView iv;
ProgressDialog progressDialog;
private ValueCallback<Uri> mUploadMessage;
private Uri mCapturedImageURI = null;
private ValueCallback<Uri[]> mFilePathCallback;
private String mCameraPhotoPath;
private static final int INPUT_FILE_REQUEST_CODE = 1;
private static final int FILECHOOSER_RESULTCODE = 1;
Timer t = new Timer();


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    CheckInternetState();
    TimerTask tt = new TimerTask() {
        @Override
        public void run() {
            switchView();
        }
    };
    t.scheduleAtFixedRate(tt, 1, 1000);
}

public void switchView() {
    Intent obj = new Intent(SecondActivity.this, noconnectionActivity.class);
    if (!DetectConnection.checkInternetConnection(this)) {
        t.cancel();
        startActivity(obj);
        webView = null;
    }
}

public void CheckInternetState() {
    if (!DetectConnection.checkInternetConnection(this)) {
        setContentView(R.layout.activity_no_connection);
    } else {
        //        Show Spinner when app is loading
        progressDialog = new ProgressDialog(this);
        progressDialog.setCancelable(true);
        progressDialog.setMessage("Loading...");
        progressDialog.show();

//             Start WebView
        StartWebView();
    }
}

public void StartWebView() {
    //        WebView to View xxx Website
    webView = (WebView) findViewById(R.id.webView);
    webView.getSettings().setJavaScriptEnabled(true);
    webView.clearCache(true);
    webView.loadUrl("http://www.doccardiacdevice.com/scan_Mobile"); // website on app launch
    webView.setWebViewClient(new xWebViewClient()); //we would be overriding WebViewClient() with custom methods
    webView.setWebChromeClient(new chromeView()); //we would be overriding WebChromeClient() with custom methods.
}

class xWebViewClient extends android.webkit.WebViewClient {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl(url);
        return true;
    }

    @Override
    public void onPageStarted(WebView view, String url, Bitmap favicon) {
        super.onPageStarted(view, url, favicon);
        progressDialog.show(); //showing the progress bar once the page has started loading
    }

    @Override
    public void onPageFinished(WebView view, String url) {
        super.onPageFinished(view, url);
        progressDialog.dismiss(); // hide the progress bar once the page has loaded
    }

    @Override
    public void onReceivedError(WebView view, WebResourceRequest request, WebResourceError error) {
        super.onReceivedError(view, request, error);
        webView.loadData("", "text/html", "utf-8"); // replace the default error page with plan content
        progressDialog.dismiss(); // hide the progress bar on error in loading
        Toast.makeText(getApplicationContext(), "Internet issue", Toast.LENGTH_SHORT).show();
        setContentView(R.layout.activity_no_connection);
    }
}

public class chromeView 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);
                Log.d("test", "Test1");

            } catch (IOException ex) {
                // Error occurred while creating the File
                Toast.makeText(getApplicationContext(), "\"Unable to create Image File", Toast.LENGTH_SHORT).show();

            }

            // 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) {
        Log.d("test", "Test2");

        mUploadMessage = uploadMsg;

        try {
            // 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);
        } catch (Exception e) {
            Log.d("test", e.getMessage());
        }

    }

    // 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);
    }

}

@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 || data.getDataString() == 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
public void onBackPressed() {
    if (webView.canGoBack()) {
        webView.goBack();
    } else {
        finish();
    }
}

private File createImageFile() throws IOException {
    try {
        // Create an image file name
        String timeStamp = new SimpleDateFormat("yyyyMMddHHmmss").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;
    } catch (Exception e) {
        Log.d("test", e.getMessage());
        return null;
    }
}

public static class DetectConnection {
    public static boolean checkInternetConnection(Context context) {
        ConnectivityManager con_manager = (ConnectivityManager)
                context.getSystemService(Context.CONNECTIVITY_SERVICE);

        return (con_manager.getActiveNetworkInfo() != null
                && con_manager.getActiveNetworkInfo().isAvailable()
                && con_manager.getActiveNetworkInfo().isConnected());
    }
}

}

Answer 1

在您的SecondActivity中，您正在执行以下操作：

setContentView(R.layout.activity_main);

并且在activity_main里面没有WebView 。

在CheckInternetState你调用setContentView(R.layout.activity_no_connection); 如果没有互联网连接。 我会说这是错误的。 无需再次尝试setContentView ，只需在该Activity的主布局中添加这些视图，并根据检查显示/隐藏这些视图。

以及导致崩溃的主要问题。 如果连接没有问题，请在CheckInternetState中调用StartWebView(); 它试图找到你的WebView ：

 webView = (WebView) findViewById(R.id.webView);

但是因为你从来没有真正调用过setContentView(R.layout.mainview); （实际放置WebView的位置）您的应用程序因错误而崩溃：

NullPointerException: Attempt to invoke virtual method 'android.webkit.WebSettings android.webkit.WebView.getSettings()' on a null object reference

因为你的WebView是 null。