来自另一个类的java 安卓调用函数

Question

我有一个主“tabHost”布局，它的框架内容设置在另一个包含webview的布局“content”上。 “Tabbar”类设置tabhost布局，“second”类设置其框架内容

问题是，当我在“Tabbar”类中尝试使用以下在参数上崩溃的代码设置webview高度时

WebView webviewA = (WebView) findViewById(R.id.webviewA);     
LayoutParams params = (LayoutParams) webviewA.getLayoutParams();
params.height -= 300;

已尝试从Tabbar中调用webviewA函数，如下所示：

Tabbar类

second recalcula = new second();
recalcula.recalcula();

二等舱

public void recalcula (){
    webviewA = (WebView) findViewById(R.id.webviewA);
    LayoutParams params = (LayoutParams) webviewA.getLayoutParams();
    params.height -= 300;
    webviewA.setLayoutParams(params);
}

也会在params上崩溃。。。我做错了什么？谢谢

logcat错误

   07-06 10:14:39.893: E/AndroidRuntime(11023): FATAL EXCEPTION: main
    07-06 10:14:39.893: E/AndroidRuntime(11023): java.lang.NullPointerException
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at com.xxxxx.projecte1.second.recalcula(second.java:70)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at com.xxxxx.projecte1.TabBar.onReceiveAd(TabBar_iOSActivity.java:493)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at com.google.ads.internal.d.B(SourceFile:1116)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at com.google.ads.internal.c$e.run(SourceFile:187)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at 安卓.os.Handler.handleCallback(Handler.java:587)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at 安卓.os.Handler.dispatchMessage(Handler.java:92)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at 安卓.os.Looper.loop(Looper.java:138)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at 安卓.app.ActivityThread.main(ActivityThread.java:3701)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at java.lang.reflect.Method.invokeNative(Native Method)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at java.lang.reflect.Method.invoke(Method.java:507)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:878)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:636)
    07-06 10:14:39.893: E/AndroidRuntime(11023):    at dalvik.system.NativeStart.main(Native Method)