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Best Practices

JS Py
Hello World
Content:
• General
• Performance
- UI
- Graphics / Animations

• Getting Help

General

- Use the cfg object to enter specific app modes immediately (See CodingFeatures for more details)
- Use app.Script to load extra source files
- Use app.Add* eqivalents to app.Create* to make your code shorter and cleaner
- Use features that DS provides you instead of doing them yourself (ie. filtering ListFolder items)
- Frequently check the debug log for any warnings or errors - especially before releasing your app (see CreateDebug)
- Use the web IDE for coding if you have a laptop because it is much easier than typing and debugging on a phone

Performance

UI

- Wrap your UI creation in app.Hide and app.Show
- Use cfg.Dark and cfg.Light for an easy Light/Dark theme setting
- Use obj.Batch to do a whole bunch of configuration calls at one shot
- Add a (optionally animated) splash screen while your app loads UI
- Use app.SetDebug(false) in your release version
- Reduce the use of app.* calls (especially in loops) as it calls the backend bridge in most cases
- Use lay.SetChildMargins and lay.SetChildTextSize to apply these properties to all children
- When initializing list controls use a precompiled item list instead of calling AddItem multiple times
- Apply styling to buttons and text boxes using the “Html” option
- Use the premium app.CreateTheme method for styling controls

Graphics / Animations

- Use app.Animate instead of setInterval
- Use img.SetAutoUpdate(false) and use manual img.Update calls
- Switch to the CreateGameView control (using cfg.Game) as its generally faster and works in web browsers too
- use the “async” option to load images

Getting Help

- Check out this documentation and the DS Wiki for any hints
- Check if your issue has been resolved before by searching keywords on Google and on the OfficialForums
- For short questions check out the Chat extension in the mobile or WiFi IDE
- For more complex questions formalize your issue in the OfficialForums
  - Always be polite, respectful and never offend any person or group of people
  - Describe your issue in a way people can understand it without knowing anything about your individual project
  - Attach screenshots and demo SPKs to your question
  - Consider putting together a minimal demo showcasing your issue

Example - GetDeviceSpecs

// https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels
var allBuilds = JSON.parse('{' +
    '"1":{"level":1,"codename":"(no code name)","version":"1.0"}, ' +
    '"2":{"level":2,"codename":"(no code name)","version":"1.1"} , ' +
    '"3":{"level":3,"codename":"Cupcake","version":"1.5"}, ' +
    '"4":{"level":4,"codename":"Donut","version":"1.6"}, ' +
    '"5":{"level":5,"codename":"Eclair","version":"2.0"}, ' +
    '"6":{"level":6,"codename":"Eclair","version":"2.0.1"}, ' +
    '"7":{"level":7,"codename":"Eclair","version":"2.1"}, ' +
    ' "8":{"level":8,"codename":"Froyo","version":"2.2.x"}, ' +
    ' "9":{"level":9,"codename":"Gingerbread","version":"2.3 - 2.3.2"}, ' +
    ' "10":{"level":10,"codename":"Gingerbread","version":"2.3.3 - 2.3.7"}, ' +
    ' "11":{"level":11,"codename":"Honeycomb","version":"3.0"}, ' +
    ' "12":{"level":12,"codename":"Honeycomb","version":"3.1"}, ' +
    ' "13":{"level":13,"codename":"Honeycomb","version":"3.2.x"}, ' +
    ' "14":{"level":14,"codename":"Ice Cream Sandwich","version":"4.0.1 - 4.0.2"}, ' +
    ' "15":{"level":15,"codename":"Ice Cream Sandwich","version":"4.0.3 - 4.0.4"}, ' +
    ' "16":{"level":16,"codename":"Jelly Bean","version":"4.1.x"}, ' +
    ' "17":{"level":17,"codename":"Jelly Bean","version":"4.2.x"}, ' +
    ' "18":{"level":18,"codename":"Jelly Bean","version":"4.3.x"}, ' +
    ' "19":{"level":19,"codename":"KitKat","version":"4.4 - 4.4.4"}, ' +
    ' "20":{"level":20,"codename":"K or L","version":"4 or 5"}, ' +
    ' "21":{"level":21,"codename":"Lollipop","version":"5.0"}, ' +
    ' "22":{"level":22,"codename":"Lollipop","version":"5.1"}, ' +
    ' "23":{"level":23,"codename":"MarshMallow","version":"6.0"}, ' +
    ' "24":{"level":24,"codename":"Nougat","version":"7.0"}, ' +
    ' "25":{"level":25,"codename":"Nougat","version":"7.1"}, ' +
    ' "26":{"level":26,"codename":"Oreo","version":"8.0"}, ' +
    ' "27":{"level":27,"codename":"Oreo","version":"8.1"}, ' +
    ' "28":{"level":28,"codename":"Pie","version":"9"}, ' +
    ' "29":{"level":29,"codename":"Q","version":"10"}, ' +
    ' "30":{"level":30,"codename":"R","version":"11"}, ' +
    ' "31":{"level":31,"codename":"S","version":"12"}, ' +
    ' "32":{"level":32,"codename":"S_V2","version":"12"} ' +
    ' }');

var osObj = allBuilds[app.GetOSVersion()]
try
{
    var osInfo = "Android " + osObj.version + " (" +
    osObj.codename + ") API level " +
    osObj.level
}
catch(err){var osInfo = app.GetOSVersion();}

var lay, txt, scroller
//Called when application is started.
function OnStart()
{
    //Create a layout with objects vertically centered.
    lay = app.CreateLayout("linear", "VCenter,FillXY");

    // create viewr for specs
    scroller = app.CreateScroller(1, 0.8);
    var specs = getDeviceSpecs();
    txt = app.CreateText(specs, 1, 0.8, "left,multiLine");
    txt.SetPadding(0.02, 0.01, 0.02, 0.01);
    //txt.SetTextColor("#ff446666");
    scroller.AddChild(txt);
    lay.AddChild(scroller);

    //Create a button and add it to layout.
    var btn = app.CreateButton("[fa-copy]", -1, -1, "fontAwesome");
    btn.SetTextSize( 32 )

    btn.SetOnTouch(btn_OnTouch);
    lay.AddChild(btn);

    //Add layout to app.    
    app.AddLayout(lay);
    OnConfig()
}

function btn_OnTouch()
{
    app.SetClipboardText(txt.GetText( ) );
    app.ShowPopup("Copied to clipboard")
}

function getBuilderVersion()
{
    var msg = "Apk Builder plugin not installed";
    var path = app.GetPrivateFolder("Plugins") +
        "/apkbuilder/Version.txt"
    if(app.FileExists(path))
    {
        msg = "Apk Builder version " + app.ReadFile( path )
    }
    else if(app.IsAPK())
    {
        msg = "APK built with " + app.GetDSVersion().toFixed(2);
    }
    return msg
}
function getDeviceSpecs()
{
    var os = app.GetOSVersion();
    var model = app.GetModel();
    var tablet = app.IsTablet();
    var fromapk = app.IsAPK();
    var isChrome = app.IsChrome();
    var isPrem = app.IsPremium();
    var isTV = app.IsTV();
    var dsversion = app.GetDSVersion().toFixed(2);
    //Get screen dimensions.
    var sw = app.GetScreenWidth();
    var sh = app.GetScreenHeight();
    var dens = app.GetScreenDensity();
    //Get display dimensions.
    var dw = app.GetDisplayWidth();
    var dh = app.GetDisplayHeight();
    //Get drive details
    var intfld = app.GetInternalFolder();
    var extfld = app.GetExternalFolder();
    var intspace = app.GetFreeSpace("internal");
    var extspace = app.GetFreeSpace("external");
    var mem = app.GetMemoryInfo().total.toLocaleString("en-US");

    //specs are formatted as a comment so we can paste
    //them somewhere convenient
    try { os = osInfo; }
    catch(err) {}
    var s = "/*\n" +
    "os=" + os + "\n" +
    getBuilderVersion() + "\n" +
    "tablet=" + tablet + "\n" +
    "model=" + model + "\n" +
    "isChrome=" + isChrome + "\n" +
    "isTV=" + isTV +"\n" +
    "DroidScript=" + dsversion + "\n" +
    "Storage access=" + storageScoped() + "\n" +
    "screen width=" + sw + "\n" +
    "screen height=" + sh + "\n" +
    "screen density=" + dens + "\n" +
    "display width=" + dw + "\n" +
    "display height=" + dh + "\n" +
    "internal folder=" + intfld + "\n" +
    "external folder=" + extfld + "\n" +
    "int free space=" + intspace + "\n" +
    "ext free space=" + extspace + "\n" +
    "memory=" + mem +"\n" +
    "premium=" + isPrem +"\n" +
    "country code=" + app.GetCountryCode() + "\n" +
    "country=" + app.GetCountry() + "\n" +
    "language code=" + app.GetLanguageCode() + "\n" +
    "language=" + app.GetLanguage() + "\n" +
    "wifi=" + app.GetIPAddress() + "\n" +
    "userAgent='" + navigator.userAgent + "'\n" +
    "*/";
    return(s);
}

function storageScoped() {
    return app.IsScoped()?"Scoped":"Traditional";
}

//called when screen rotates
//also called at startup to fix Chromebook display size anomaly
function OnConfig()
{
    var fixwid = lay.GetAbsWidth()/app.GetDisplayWidth();
    var fixhigh = lay.GetAbsHeight()/app.GetDisplayHeight();
    var wid = 1, high = 0.8;
    if (fixwid<1) wid *= fixwid; // chromebook not using full width
    if (fixhigh<1) high *= fixhigh; // or height
    scroller.SetSize( wid,high );
    txt.SetSize( wid, high );
}
# https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels
allBuilds = JSON.parse('' +
    '"1":"level":1,"codename":"(no code name)","version":"1.0", ' +
    '"2":"level":2,"codename":"(no code name)","version":"1.1", ' +
    '"3":"level":3,"codename":"Cupcake","version":"1.5", ' +
    '"4":"level":4,"codename":"Donut","version":"1.6", ' +
    '"5":"level":5,"codename":"Eclair","version":"2.0", ' +
    '"6":"level":6,"codename":"Eclair","version":"2.0.1", ' +
    '"7":"level":7,"codename":"Eclair","version":"2.1", ' +
    ' "8":"level":8,"codename":"Froyo","version":"2.2.x", ' +
    ' "9":"level":9,"codename":"Gingerbread","version":"2.3 - 2.3.2", ' +
    ' "10":"level":10,"codename":"Gingerbread","version":"2.3.3 - 2.3.7", ' +
    ' "11":"level":11,"codename":"Honeycomb","version":"3.0", ' +
    ' "12":"level":12,"codename":"Honeycomb","version":"3.1", ' +
    ' "13":"level":13,"codename":"Honeycomb","version":"3.2.x", ' +
    ' "14":"level":14,"codename":"Ice Cream Sandwich","version":"4.0.1 - 4.0.2", ' +
    ' "15":"level":15,"codename":"Ice Cream Sandwich","version":"4.0.3 - 4.0.4", ' +
    ' "16":"level":16,"codename":"Jelly Bean","version":"4.1.x", ' +
    ' "17":"level":17,"codename":"Jelly Bean","version":"4.2.x", ' +
    ' "18":"level":18,"codename":"Jelly Bean","version":"4.3.x", ' +
    ' "19":"level":19,"codename":"KitKat","version":"4.4 - 4.4.4", ' +
    ' "20":"level":20,"codename":"K or L","version":"4 or 5", ' +
    ' "21":"level":21,"codename":"Lollipop","version":"5.0", ' +
    ' "22":"level":22,"codename":"Lollipop","version":"5.1", ' +
    ' "23":"level":23,"codename":"MarshMallow","version":"6.0", ' +
    ' "24":"level":24,"codename":"Nougat","version":"7.0", ' +
    ' "25":"level":25,"codename":"Nougat","version":"7.1", ' +
    ' "26":"level":26,"codename":"Oreo","version":"8.0", ' +
    ' "27":"level":27,"codename":"Oreo","version":"8.1", ' +
    ' "28":"level":28,"codename":"Pie","version":"9", ' +
    ' "29":"level":29,"codename":"Q","version":"10", ' +
    ' "30":"level":30,"codename":"R","version":"11", ' +
    ' "31":"level":31,"codename":"S","version":"12", ' +
    ' "32":"level":32,"codename":"S_V2","version":"12"' +
    '')

osObj = allBuilds[app.GetOSVersion()]
try:
    osInfo = "Android " + osObj.version + " (" +
    osObj.codename + ") API level " +
    osObj.level
except err)osInfo = app.GetOSVersion(: pass

lay, txt, scroller
# Called when application is started.
def OnStart():
    # Create a layout with objects vertically centered.
    lay = app.CreateLayout("linear", "VCenter,FillXY")

    # create viewr for specs
    scroller = app.CreateScroller(1, 0.8)
    specs = getDeviceSpecs()
    txt = app.CreateText(specs, 1, 0.8, "left,multiLine")
    txt.SetPadding(0.02, 0.01, 0.02, 0.01)
    # txt.SetTextColor("#ff446666")
    scroller.AddChild(txt)
    lay.AddChild(scroller)

    # Create a button and add it to layout.
    btn = app.CreateButton("[fa-copy]", -1, -1, "fontAwesome")
    btn.SetTextSize( 32 )

    btn.SetOnTouch(btn_OnTouch)
    lay.AddChild(btn)

    # Add layout to app.    
    app.AddLayout(lay)
    OnConfig()

def btn_OnTouch():
    app.SetClipboardText(txt.GetText( ) )
    app.ShowPopup("Copied to clipboard")

def getBuilderVersion():
    msg = "Apk Builder plugin not installed"
    path = app.GetPrivateFolder("Plugins") +
        "/apkbuilder/Version.txt"
    if app.FileExists(path):
        msg = "Apk Builder version " + app.ReadFile( path )
    elif app.IsAPK():
        msg = "APK built with " + app.GetDSVersion().toFixed(2)
    return msg
def getDeviceSpecs():
    os = app.GetOSVersion()
    model = app.GetModel()
    tablet = app.IsTablet()
    fromapk = app.IsAPK()
    isChrome = app.IsChrome()
    isPrem = app.IsPremium()
    isTV = app.IsTV()
    dsversion = app.GetDSVersion().toFixed(2)
    # Get screen dimensions.
    sw = app.GetScreenWidth()
    sh = app.GetScreenHeight()
    dens = app.GetScreenDensity()
    # Get display dimensions.
    dw = app.GetDisplayWidth()
    dh = app.GetDisplayHeight()
    # Get drive details
    intfld = app.GetInternalFolder()
    extfld = app.GetExternalFolder()
    intspace = app.GetFreeSpace("internal")
    extspace = app.GetFreeSpace("external")
    mem = app.GetMemoryInfo().total.toLocaleString("en-US")

    # specs are formatted as a comment so we can paste
    # them somewhere convenient
    tryos = osInfo
    except err:
    s = "/*\n" +
    "os=" + os + "\n" +
    getBuilderVersion() + "\n" +
    "tablet=" + tablet + "\n" +
    "model=" + model + "\n" +
    "isChrome=" + isChrome + "\n" +
    "isTV=" + isTV +"\n" +
    "DroidScript=" + dsversion + "\n" +
    "Storage access=" + storageScoped() + "\n" +
    "screen width=" + sw + "\n" +
    "screen height=" + sh + "\n" +
    "screen density=" + dens + "\n" +
    "display width=" + dw + "\n" +
    "display height=" + dh + "\n" +
    "internal folder=" + intfld + "\n" +
    "external folder=" + extfld + "\n" +
    "int free space=" + intspace + "\n" +
    "ext free space=" + extspace + "\n" +
    "memory=" + mem +"\n" +
    "premium=" + isPrem +"\n" +
    "country code=" + app.GetCountryCode() + "\n" +
    "country=" + app.GetCountry() + "\n" +
    "language code=" + app.GetLanguageCode() + "\n" +
    "language=" + app.GetLanguage() + "\n" +
    "wifi=" + app.GetIPAddress() + "\n" +
    "userAgent='" + navigator.userAgent + "'\n" +
    "*/"
    return(s)

def storageScoped():
    return app.IsScoped()?"Scoped":"Traditional"

# called when screen rotates
# also called at startup to fix Chromebook display size anomaly
def OnConfig():
    fixwid = lay.GetAbsWidth()/app.GetDisplayWidth()
    fixhigh = lay.GetAbsHeight()/app.GetDisplayHeight()
    wid = 1, high = 0.8
    if fixwid<1: wid *= fixwid; # chromebook not using full width
    if fixhigh<1: high *= fixhigh; # or height
    scroller.SetSize( wid,high )
    txt.SetSize( wid, high )
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