Question

我开发了一个来自android stuido的简单webview应用程序，它将在线时加载页面的url并在离线时显示缓存文件。但是我得到了

的常数错误

print "".join(typed_num)

以下是我的Mainactivity .java代码

 Null pointer Exception
    at java.lang.reflect.Method.invoke(Native Method)                                                                           
atcom.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit
.java:726)                                                                                 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

并从我的manifest.xml文件

package com.example.sagar.cdproutine;

import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.WebSettings;
import android.webkit.WebView;

public class MainActivity extends AppCompatActivity {

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

        Context context = null;
        WebView webView = new WebView(context);
        webView.getSettings().setAppCacheMaxSize(5 * 1024 * 1024); // 5MB
        webView.getSettings().setAppCachePath(
            getApplicationContext().getCacheDir().getAbsolutePath());
        webView.getSettings().setAllowFileAccess(true);
        webView.getSettings().setAppCacheEnabled(true);
        webView.getSettings().setJavaScriptEnabled(true);
        webView.getSettings().setCacheMode(WebSettings.LOAD_DEFAULT); // load online by default

        if (!isNetworkAvailable()) { // loading offline
            webView.getSettings().setCacheMode(
                WebSettings.LOAD_CACHE_ELSE_NETWORK);
        }

        webView.loadUrl("http://www.sagarrawal.com.np");
    }

    private boolean isNetworkAvailable() {
        ConnectivityManager connectivityManager = (ConnectivityManager)
        getSystemService(CONNECTIVITY_SERVICE);
        NetworkInfo activeNetworkInfo =
            connectivityManager.getActiveNetworkInfo();
        return activeNetworkInfo != null;
    }
}

我认为Context导致问题，但我不知道如何解决它。任何帮助都会受到很大的赞赏。

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.sagar.cdproutine">

<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>

Answer 1

我错过了什么吗？此处的此行为空，您将其传递给Web视图。

Context context = null;

尝试这样的事情：

WebView webView = new WebView（getApplicationContext（））;

Answer 2

正如David所提到的那样，不传递null Context

这是在OnCreate

webView = (WebView) findViewById(R.id.webView);
initWebView();//Initialize the WebView
webView.loadUrl(url);//pass your Url

对于initWebView（）;

private void initWebView() {
    webView.setWebChromeClient(new MyWebChromeClient(this));
    webView.setWebViewClient(new WebViewClient() {
        @Override
        public void onPageStarted(WebView view, String url, Bitmap favicon) {
            super.onPageStarted(view, url, favicon);        
        }

        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            webView.loadUrl(url);
            return true;
        }

        @Override
        public void onPageFinished(WebView view, String url) {
            super.onPageFinished(view, url);
        }

        @Override
        public void onReceivedError(WebView view, WebResourceRequest request, WebResourceError error) {
            super.onReceivedError(view, request, error);
        }
    });
    webView.clearCache(true);
    webView.clearHistory();
    webView.getSettings().setJavaScriptEnabled(true);
    webView.setHorizontalScrollBarEnabled(false);
}

对于MyWebChromeClient，请执行以下操作：

private class MyWebChromeClient extends WebChromeClient {
    Context context;

    public MyWebChromeClient(Context context) {
        super();
        this.context = context;
    }


}

另请参阅此引用 - link

编译时出现空指针异常

2 个答案: