如何实例化自定义WebView

Question

我正在尝试创建一个覆盖onScrollChanged方法的自定义WebView。但是当我尝试实例化它时，我得到以下错误:

06-13 17:30:09.977: E/AndroidRuntime(20366): FATAL EXCEPTION: main
06-13 17:30:09.977: E/AndroidRuntime(20366): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{br.com.facilit.target.app.android/br.com.facilit.target.app.android.BrowserActivity}: java.lang.NullPointerException
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1880)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.os.Handler.dispatchMessage(Handler.java:99)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.os.Looper.loop(Looper.java:137)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.app.ActivityThread.main(ActivityThread.java:4424)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at java.lang.reflect.Method.invokeNative(Native Method)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at java.lang.reflect.Method.invoke(Method.java:511)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at dalvik.system.NativeStart.main(Native Method)
06-13 17:30:09.977: E/AndroidRuntime(20366): Caused by: java.lang.NullPointerException
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.content.ContextWrapper.getResources(ContextWrapper.java:81)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.view.View.<init>(View.java:2696)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.view.View.<init>(View.java:2744)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.view.ViewGroup.<init>(ViewGroup.java:385)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.widget.AbsoluteLayout.<init>(AbsoluteLayout.java:52)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.webkit.WebView.<init>(WebView.java:1119)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.webkit.WebView.<init>(WebView.java:1102)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.webkit.WebView.<init>(WebView.java:1091)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.webkit.WebView.<init>(WebView.java:1081)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.webkit.WebView.<init>(WebView.java:1072)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at br.com.facilit.target.app.android.CustomizedWebView.<init>(CustomizedWebView.java:12)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at br.com.facilit.target.app.android.BrowserActivity.<init>(BrowserActivity.java:29)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at java.lang.Class.newInstanceImpl(Native Method)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at java.lang.Class.newInstance(Class.java:1319)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.app.Instrumentation.newActivity(Instrumentation.java:1023)
06-13 17:30:09.977: E/AndroidRuntime(20366):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1871)
06-13 17:30:09.977: E/AndroidRuntime(20366):    ... 11 more

我的自定义webview代码:

public class CustomizedWebView extends WebView {
    public CustomizedWebView(Context context) {
        super(context);
    }
    public CustomizedWebView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        Log.d(Constants.BROWSER_ACTIVITY, "SCROLL CHANGED");
        super.onScrollChanged(l, t, oldl, oldt);
    }
}

如何实例化它:

public class BrowserActivity extends Activity {
    private MetaDados metaDado;
    String url;
    CustomizedWebView webView = new CustomizedWebView(this);
    ProgressBar progressUrl;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_browser);
        final ActionBar actionBar = getActionBar();
        actionBar.setDisplayHomeAsUpEnabled(true);
        progressUrl = (ProgressBar) findViewById(R.id.progressUrl);
        Bundle extras = getIntent().getExtras();
        if (extras != null) {
            metaDado = extras.getParcelable("metaDado");
        }
        TextView browserTitle = (TextView) findViewById(R.id.browser_title);
        browserTitle.setText(metaDado.getName());
        webView = (CustomizedWebView) findViewById(R.id.webView1);
        webView.getSettings().setJavaScriptEnabled(true);
        webView.getSettings().setBuiltInZoomControls(true);
        webView.getSettings().setSupportZoom(true);
        webView.getSettings().setUseWideViewPort(true);
        webView.getSettings().setLoadWithOverviewMode(true);
        if (metaDado.getType().equals(Constants.FULL)) {
            url = "file://" + Constants.DEST_PATH_PARENT + "/" + metaDado.getUuidInstituicao() + "/full/"
                    + metaDado.getOfflineUuid() + "/index.html";
        } else if (metaDado.getType().equals(Constants.PRES)) {
            url = "file://" + Constants.DEST_PATH_PARENT + "/" + metaDado.getUuidInstituicao() + "/pres/"
                    + metaDado.getOfflineUuid() + "/" + metaDado.getOfflineUuid() + "/index.html";
        }
        webView.setWebViewClient(new WebViewClient() {
            @Override
            public void onPageStarted(WebView view, String url, Bitmap favicon) {
                progressUrl.setVisibility(View.VISIBLE);
                super.onPageStarted(view, url, favicon);
            }
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                view.loadUrl(url);
                return true;
            }
            @Override
            public void onPageFinished(WebView view, String url) {
                super.onPageFinished(view, url);
                progressUrl.setVisibility(View.GONE);
            }
        });
        webView.loadUrl(url);
        addListeners();
    }
    private void addListeners() {
        Button goBack = (Button) findViewById(R.id.back);
        Button goForward = (Button) findViewById(R.id.forward);
        goForward.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                if (webView.canGoForward()) {
                    webView.goForward();
                }
            }
        });
        goBack.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                if (webView.canGoBack()) {
                    webView.goBack();
                }
            }
        });
    }
}

My xml file:

 <br.com.facilit.target.app.android.CustomizedWebView
     android:id="@+id/webView1"
     android:layout_below="@id/header"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     android:clickable="true"
     />

Answer 1

删除

CustomizedWebView webView = new CustomizedWebView(this);

如果看起来不需要，或者将new CustomizedWebView(this)移动到onCreate(savedInstanceState)

中调用

在活动类初始化期间，您的上下文没有完全初始化