constructor() {
        disable();
        // >> setting-specific-tracing-categories
        setCategories(categories.concat(
            categories.Binding,
            categories.Layout,
            categories.Style,
            categories.ViewHierarchy,
            categories.VisualTreeEvents
        ));
        enable();
        // << setting-specific-tracing-categories

        // >> trace-add-categories
        addCategories(categories.Navigation);
        // << trace-add-categories

        setTimeout(function () {
            console.log("-----------------------------------------------------");
            console.log("New trace category has been added");
            console.log("Category: NativeLifecycle");
            console.log("-----------------------------------------------------");
            alert("NativeLifecycle trace category has been added.");
            addCategories(categories.NativeLifecycle);
        }, 2000);

        write("I (heart) NativeScript!", categories.Debug);
    }

 onMeasure(widthMeasureSpec, heightMeasureSpec) {
   let utils = require("utils/utils"),
     width = utils.layout.getMeasureSpecSize(widthMeasureSpec),
     widthMode = utils.layout.getMeasureSpecMode(widthMeasureSpec),
     height = utils.layout.getMeasureSpecSize(heightMeasureSpec),
     heightMode = utils.layout.getMeasureSpecMode(heightMeasureSpec),
     nativeWidth = this.nativeView ? (this.nativeView.image ? this.nativeView.image.size.width : 0) : 0,
     nativeHeight = this.nativeView ? (this.nativeView.image ? this.nativeView.image.size.height : 0) : 0,
     measureWidth = Math.max(nativeWidth, this.minWidth as number),
     measureHeight = Math.max(nativeHeight, this.minHeight as number),
     finiteWidth = widthMode !== utils.layout.UNSPECIFIED,
     finiteHeight = heightMode !== utils.layout.UNSPECIFIED;
   if (nativeWidth !== 0 && nativeHeight !== 0 && (finiteWidth || finiteHeight)) {
     let scale = this.computeScaleFactor(width, height, finiteWidth, finiteHeight, nativeWidth, nativeHeight, this.stretch),
       resultW = Math.floor(nativeWidth * scale.width),
       resultH = Math.floor(nativeHeight * scale.height);
     measureWidth = finiteWidth ? Math.min(resultW, width) : resultW;
     measureHeight = finiteHeight ? Math.min(resultH, height) : resultH;
     let trace = require("trace");
     trace.write("Image stretch: " + this.stretch +
       ", nativeWidth: " + nativeWidth +
       ", nativeHeight: " + nativeHeight, trace.categories.Layout);
   }
   let view = require("ui/core/view");
   let widthAndState = view.View.resolveSizeAndState(measureWidth, width, widthMode, 0);
   let heightAndState = view.View.resolveSizeAndState(measureHeight, height, heightMode, 0);
   this.setMeasuredDimension(widthAndState, heightAndState);
 }

function _testTransition(navigationTransition: NavigationTransition) {
    var testId = `Transition[${JSON.stringify(navigationTransition)}]`;
    trace.write(`Testing ${testId}`, trace.categories.Test);
    var navigationEntry: NavigationEntry = {
        create: function (): Page {
            let page = new Page();
            page.id = testId;
            page.style.backgroundColor = new Color(255, Math.round(Math.random() * 255), Math.round(Math.random() * 255), Math.round(Math.random() * 255));
            return page;
        },
        animated: true,
        transition: navigationTransition
    }

    helper.navigateWithEntry(navigationEntry);
    TKUnit.wait(0.100);
}

export function rendererError(message: string): void {
    write(message, rendererTraceCategory, messageType.error);
}

export function rendererLog(msg): void {
    write(msg, rendererTraceCategory);
}

export function styleError(message: string): void {
    write(message, categories.Style, messageType.error);
}

export function routerLog(message: string): void {
    write(message, routerTraceCategory);
}

function log(message: string) {
    trace.write(message, CATEGORY);
}

export function listViewLog(message: string): void {
    write(message, listViewTraceCategory);
}