安卓视频WebView FullScreen不工作-未调用onShowCustomView()

public class CustomWebChromeClient extends WebChromeClient {
    private View mCustomView;
    private Activity mActivity;

    public CustomWebChromeClient(Activity activity) {
        mActivity = activity;
    }

    @Override
    public void onShowCustomView(View view, CustomViewCallback callback) {
        if (mCustomView != null) {
            callback.onCustomViewHidden();
            return;
        }

        mCustomView = view;
        mCustomView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_FULLSCREEN);
        mActivity.setContentView(mCustomView);
    }

    @Override
    public void onHideCustomView() {
        if (mCustomView == null) {
            return;
        }

        mCustomView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_VISIBLE);
        mActivity.setContentView(mCustomView);
        mCustomView = null;
    }
}

WebView webView = findViewById(R.id.webView);
webView.setWebChromeClient(new CustomWebChromeClient(this));