我刚刚开始使用
Android SDK.我想用WebView创建一个只显示本地网页的简单应用程序.我已经使用了我在网上找到的例子来制作它.
该应用程序工作得很好,直到我想添加一个后退按钮.当按下电话后退按钮时,应用程序崩溃.
这是我的MainActivity.java
package com.hspd.avhor;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.webkit.WebView;
import android.webkit.WebViewClient;
public class MainActivity extends Activity {
WebView wv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
WebView wv = (WebView)findViewById(R.id.hspd_webview);
wv.setWebViewClient(new WebViewClient() {
@Override
public boolean shouldOverrideUrlLoading(WebView view,String url){
view.loadUrl(url);
return true;
}
});
wv.loadUrl("file:///android_asset/one.htm");
}
@Override
public void onBackPressed()
{
if(wv.canGoBack())
wv.goBack();
else
super.onBackPressed();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main,menu);
return true;
}
}
这是我的activity_main.xml：
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fillViewport="true"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<WebView
android:id="@+id/hspd_webview"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</ScrollView>
这是我在logcat中的错误：
04-22 17:48:06.953: W/dalvikvm(799): threadid=1: thread exiting with uncaught exception (group=0x40a71930) 04-22 17:48:06.972: E/AndroidRuntime(799): FATAL EXCEPTION: main 04-22 17:48:06.972: E/AndroidRuntime(799): java.lang.NullPointerException 04-22 17:48:06.972: E/AndroidRuntime(799): at com.hspd.avhor.MainActivity.onKeyDown(MainActivity.java:41) 04-22 17:48:06.972: E/AndroidRuntime(799): at android.view.KeyEvent.dispatch(KeyEvent.java:2609) 04-22 17:48:06.972: E/AndroidRuntime(799): at android.app.Activity.dispatchKeyEvent(Activity.java:2375) 04-22 17:48:06.972: E/AndroidRuntime(799): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1847) 04-22 17:48:06.972: E/AndroidRuntime(799): at android.view.ViewRootImpl.deliverKeyEventPostIme(ViewRootImpl.java:3701) 04-22 17:48:06.972: E/AndroidRuntime(799): at android.view.ViewRootImpl.handleImeFinishedEvent(ViewRootImpl.java:3651) 04-22 17:48:06.972: E/AndroidRuntime(799): at android.view.ViewRootImpl$ViewRootHandler.handleMessage(ViewRootImpl.java:2818) 04-22 17:48:06.972: E/AndroidRuntime(799): at android.os.Handler.dispatchMessage(Handler.java:99) 04-22 17:48:06.972: E/AndroidRuntime(799): at android.os.Looper.loop(Looper.java:137) 04-22 17:48:06.972: E/AndroidRuntime(799): at android.app.ActivityThread.main(ActivityThread.java:5041) 04-22 17:48:06.972: E/AndroidRuntime(799): at java.lang.reflect.Method.invokeNative(Native Method) 04-22 17:48:06.972: E/AndroidRuntime(799): at java.lang.reflect.Method.invoke(Method.java:511) 04-22 17:48:06.972: E/AndroidRuntime(799): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 04-22 17:48:06.972: E/AndroidRuntime(799): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 04-22 17:48:06.972: E/AndroidRuntime(799): at dalvik.system.NativeStart.main(Native Method)
提前致谢 ：)
解决方法
覆盖onKeyDown(params),检查按下的键是否为后退按钮,检查webview是否可以导航到上一页,如果是,则导航到上一页.如果没有要显示的网页,您可以完成活动
您可以使用以下
@Override
public boolean onKeyDown(int keyCode,KeyEvent event) {
if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) {
//if Back key pressed and webview can navigate to prevIoUs page
webView.goBack();
// go back to prevIoUs page
return true;
}
else
{
finish();
// finish the activity
}
return super.onKeyDown(keyCode,event);
}
编辑：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
<WebView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/wv"></WebView>
</LinearLayout>
编辑：2
这是一个有效的样本.在三星galaxy s3上测试过
activtiy_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity" > <WebView android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_centerHorizontal="true" android:layout_centerVertical="true" android:id="@+id/wv"/> </RelativeLayout>
主要活动
public class MainActivity extends Activity {
private WebView webView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
webView = (WebView) findViewById(R.id.wv);
webView.getSettings().setJavaScriptEnabled(true);
webView.setWebChromeClient(new WebChromeClient() {
public void onProgressChanged(WebView view,int progress) {
MainActivity.this.setProgress(progress * 1000);
}
});
webView.setWebViewClient(new WebViewClient() {
public void onReceivedError(WebView view,int errorCode,String description,String failingUrl) {
Toast.makeText(MainActivity.this,"Oh no! " + description,Toast.LENGTH_SHORT).show();
}
});
webView.loadUrl("http://slashdot.org/");
}
@Override
public boolean onKeyDown(int keyCode,KeyEvent event) {
if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) {
webView.goBack();
return true;
}
else
{
finish();
}
return super.onKeyDown(keyCode,event);
}
}
