Java 在Webview中加载ProgresBar

我有问题。 我在Main2活动中执行progressbar。 应用程序启动，但当网站加载时，progressbar不会消失。 我的应用程序崩溃了。 请帮忙* 我想更正我的代码，因为这是了解哪里出错的最好方法。 谢谢

代码如下：

    package musial.pzstis.com.pzstiz;

import android.app.Activity;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ProgressBar;

/*
 * Demo of creating an application to open any URL inside the application and clicking on any link from that URl
should not open Native browser but  that URL should open in the same screen.

- Load WebView with progress bar
 */
public class Main2Activity extends Activity {
    /** Called when the activity is first created. */

    WebView myWebView;
    ProgressBar progressBar;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        myWebView = (WebView) findViewById(R.id.webView);
        progressBar = (ProgressBar) findViewById(R.id.progressBar7);

        myWebView.setWebViewClient(new myWebClient());
        myWebView.getSettings().setJavaScriptEnabled(true);
        WebSettings webSettings = myWebView.getSettings();
        myWebView.loadUrl("https://docs.google.com/viewer?url=http%3A%2F%2Fpzstiz.swiebodzin.pl%2Fzastepstwa%2FPZSTiZ_zastepstwa.pdf");
        webSettings.setBuiltInZoomControls(true);
        webSettings.setSupportZoom(true);
        myWebView.getSettings().setCacheMode(WebSettings.LOAD_NO_CACHE);
        myWebView.getSettings().setRenderPriority(WebSettings.RenderPriority.HIGH);

    }

    public class myWebClient extends WebViewClient
    {
        @Override
        public void onPageStarted(WebView view, String url, Bitmap favicon) {
            // TODO Auto-generated method stub
            super.onPageStarted(view, url, favicon);
        }

        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            // TODO Auto-generated method stub
            progressBar.setVisibility(View.VISIBLE);
            view.loadUrl(url);
            return true;

        }

        @Override
        public void onPageFinished(WebView view, String url) {
            // TODO Auto-generated method stub
            super.onPageFinished(view, url);

            progressBar.setVisibility(View.GONE);
        }
    }

    // To handle "Back" key press event for WebView to go back to previous screen.
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event)
    {
        if ((keyCode == KeyEvent.KEYCODE_BACK) && myWebView.canGoBack()) {
            myWebView.goBack();
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }
}

有以下日志：

    02-14 20:43:38.592 20262-20299/musial.pzstis.com.pzstiz E/EGL_emulation: tid 20299: eglSurfaceAttrib(1174): error 0x3009 (EGL_BAD_MATCH)
02-14 20:43:44.672 20262-20262/musial.pzstis.com.pzstiz E/AndroidRuntime: FATAL EXCEPTION: main
                                                                          Process: musial.pzstis.com.pzstiz, PID: 20262
                                                                          java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setVisibility(int)' on a null object reference
                                                                              at musial.pzstis.com.pzstiz.Main2Activity$myWebClient.onPageFinished(Main2Activity.java:66)
                                                                              at com.android.webview.chromium.WebViewContentsClientAdapter.onPageFinished(WebViewContentsClientAdapter.java:531)
                                                                              at org.chromium.android_webview.AwContentsClientCallbackHelper$MyHandler.handleMessage(AwContentsClientCallbackHelper.java:188)
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                              at android.os.Looper.loop(Looper.java:154)
                                                                              at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                              at java.lang.reflect.Method.invoke(Native Method)
                                                                              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
02-14 20:43:44.777 1569-4538/system_process E/EGL_emulation: tid 4538: eglSurfaceAttrib(1174): error 0x3009 (EGL_BAD_MATCH)

---

如果progressbar出现空指针异常，我将以以下形式封装对progressbar的所有访问：

if(progressBar == null)
    progressBar = (ProgressBar) findViewById(R.id.progressBar7);
if(progressBar)
    progressBar.setVisibility(View.GONE);

在vour代码中实现：

public class Main2Activity extends Activity {
/** Called when the activity is first created. */

WebView myWebView;
ProgressBar progressBar;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);

    myWebView = (WebView) findViewById(R.id.webView);
    progressBar = (ProgressBar) findViewById(R.id.progressBar7);

    myWebView.setWebViewClient(new myWebClient(this));
    myWebView.getSettings().setJavaScriptEnabled(true);
    WebSettings webSettings = myWebView.getSettings();
    myWebView.loadUrl("https://docs.google.com/viewer?url=http%3A%2F%2Fpzstiz.swiebodzin.pl%2Fzastepstwa%2FPZSTiZ_zastepstwa.pdf");
    webSettings.setBuiltInZoomControls(true);
    webSettings.setSupportZoom(true);
    myWebView.getSettings().setCacheMode(WebSettings.LOAD_NO_CACHE);
    myWebView.getSettings().setRenderPriority(WebSettings.RenderPriority.HIGH);

}

public class myWebClient extends WebViewClient
{

    privat Activity main2ac;
    ProgressBar progressBar;

    public myWebClient(Activity handle){
        main2ac = handle;
    }

    @Override
    public void onPageStarted(WebView view, String url, Bitmap favicon) {
        // TODO Auto-generated method stub
        super.onPageStarted(view, url, favicon);
    }

    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
    // TODO Auto-generated method stub

        if(progressBar == null)
            progressBar = (ProgressBar)main2ac.findViewById(R.id.progressBar7);
        if(progressBar)
            progressBar.setVisibility(View.VISIBLE);
        view.loadUrl(url);
        return true;
    }

    @Override
    public void onPageFinished(WebView view, String url) {
        // TODO Auto-generated method stub
        super.onPageFinished(view, url);

        if(progressBar == null)
            progressBar = (ProgressBar)main2ac.findViewById(R.id.progressBar7);
        if(progressBar)
            progressBar.setVisibility(View.GONE);
    }
}

---

将progressBar传递到自定义webview：

myWebView.setWebViewClient(new myWebClient(progressBar));

将myWebClient类更改为：

public class myWebClient extends WebViewClient {
     private ProgressBar progressBar;

    public myWebClient(ProgressBar progressBar) {
        this.progressBar=progressBar;
        progressBar.setVisibility(View.VISIBLE);
    }
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        // TODO Auto-generated method stub
        view.loadUrl(url);
        return true;
    }

    @Override
    public void onPageFinished(WebView view, String url) {
        // TODO Auto-generated method stub
        super.onPageFinished(view, url);
        progressBar.setVisibility(View.GONE);
    }
}

---

希望这有帮助。

我不明白。Hmmm您可以在代码中添加/编辑吗？java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“void android.widget.ProgressBar.setVisibility（int）”，通过myWebView.setWebViewClient（新的myWebClient（ProgressBar））中的ProgressBar；现在，当我单击此按钮以停止此活动应用程序时。有来自监视器的代码。java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“void android.widget.ProgressBar.setVisibility（int）”，是否确实已在布局“activity\u main\u 2.xml”中添加id为“progressBar7”的ProgressBar？（只是检查一下）