How do you properly write and use a View subclass in Android?

问题

I am trying to implement one of the solutions found here.

My problem is that I'm not sure if I am implementing and using my subclass correctly. I am subclassing a WebView here:

public class myWebView extends WebView{

  public myWebView(Context context) {
    super(context);
    // TODO Auto-generated constructor stub
}

  @Override
protected void onSizeChanged(int w, int h, int ow, int oh) {
    // TODO Auto-generated method stub

      scrollTo(xScroll - (widthScroll/2), yScroll - (heightScroll/2));


    super.onSizeChanged(w, h, ow, oh);
}

   }}

It should be private but forget that for now. I have the code inside of one of my activities that has an inner webview in the view hierarchy. Outside of the onCreate method of that activity.

Inside the onCreate method, I have:myWebView mapImage = (myWebView) findViewById(R.id.mapcroppic);

This gives me a ClassCastException for that call. (Does the xml layout file need to use <myWebView>? Can it?) How do I use this the correct way?

回答1:

(Does the xml layout file need to use <myWebView>? Can it?) How do I use this the correct way?

Yes:

<your.package.name.myWebView
    android:layout_with="blah"/>

Well, that works if the myWebView is a public class. If it's an inner one:

<view class="your.package.name.myWebView.YourActivity$myWebView" />

来源：https://stackoverflow.com/questions/4731082/how-do-you-properly-write-and-use-a-view-subclass-in-android