> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/xamarin/ui-customization/thumbnail-slider.md).

# Thumbnail slider

Learn how to add a PDF page slider in Xamarin.Android with this tutorial. Customize slider buttons, set up layout, and create event listeners for a seamless user experience. The Apryse Xamarin SDK str

You can use the slider to get a thumbnail review of pages before they are actually shown in the viewer.

{% tabs %}
{% tab title="Android" %}

## Adding PDF page slider in Xamarin.Android

{% hint style="info" %}
**This tutorial only applies to Xamarin.Android. See Xamarin.iOS equivalent here .**
{% endhint %}

[`ThumbnailSlider`](https://sdk.apryse.com/api/xamarinandroid/tools/api/pdftron.PDF.Widget.Seekbar.DocumentSlider.html) is a [`LinearLayout`](https://developer.android.com/reference/android/widget/LinearLayout.html) that contains an [`AppCompatSeekBar`](https://developer.android.com/reference/androidx/appcompat/widget/AppCompatSeekBar/) to change pages, and two [`AppCompatImageButton`](https://developer.android.com/reference/androidx/appcompat/widget/AppCompatImageButton/) on the left and right side. When sliding the seekbar, it displays a small page preview on top of the thumbnail slider.

![](https://653871032-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FgjsBtuYmcKhWOdM9VCg4%2Fuploads%2Fgit-blob-8d9a5332f5f0f19b7366a42dff2c60c5f53be78a%2F2a26a9c2e25e146ff678eb03af5c39fc52d55587-420x540.gif?alt=media)

## Show thumbnail slider

To set up your layout with the thumbnail slider, add a `<ThumbnailSlider>` element to your XML layout. For example, your layout may look like this:

{% code lineNumbers="true" %}

```xml
<com.pdftron.pdf.controls.ThumbnailSlider android:id="@+id/thumbnailSlider" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true"/>
```

{% endcode %}

Then, attach a [`PDFViewCtrl`](https://sdk.apryse.com/api/xamarinandroid/pdfnet/api/pdftron.PDF.PDFViewCtrl.html) to the thumbnail slider. If [`PDFViewCtrl`](https://sdk.apryse.com/api/xamarinandroid/pdfnet/api/pdftron.PDF.PDFViewCtrl.html) is in the same layout, you can set it by adding the [`app:pdfviewctrlId`](#change-thumbnail-slider-buttons) attribute:

{% code lineNumbers="true" %}

```xml
<com.pdftron.pdf.controls.ThumbnailSlider android:id="@+id/thumbnailSlider" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true" app:pdfviewctrlId="@id/pdfviewctrl"/>
```

{% endcode %}

If [`PDFViewCtrl`](https://sdk.apryse.com/api/xamarinandroid/pdfnet/api/pdftron.PDF.PDFViewCtrl.html) is **not** in the same layout, you can programmatically set it to a thumbnail slider by calling `setPdfViewCtrl(PDFViewCtrl)`:

{% code lineNumbers="true" %}

```csharp
var thumbnailSlider = FindViewById<ThumbnailSlider>(Resource.Id.thumbnailSlider);
thumbnailSlider.SetPdfViewCtrl(mPdfViewCtrl);
```

{% endcode %}

## Change thumbnail slider buttons

You can change the image drawable of the left menu item and right menu item buttons by adding the [`app:leftMenuItemDrawable`](https://docs.apryse.com) and [`app:rightMenuItemDrawable`](https://docs.apryse.com) attributes in your xml layout.

**Example**

{% code lineNumbers="true" %}

```xml
<com.pdftron.pdf.controls.ThumbnailSlider android:id="@+id/thumbnailSlider" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true" app:leftMenuItemDrawable="@drawable/left_icon" app:rightMenuItemDrawable="@drawable/right_icon"/>
```

{% endcode %}

Additionally, you can remove the left and right slider buttons by setting the drawables to null:

{% code lineNumbers="true" %}

```csharp
<com.pdftron.pdf.controls.ThumbnailSlider android:id="@+id/thumbnailSlider" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true" app:leftMenuItemDrawable="@null" app:rightMenuItemDrawable="@null"/>
```

{% endcode %}

You can also change the buttons programmatically by calling `setMenuItem(@DrawableRes int, @MenuItemPosition int)`. The second parameter determines the position of the button which is either `POSITION_LEFT` or `POSITION_RIGHT`.

**Example**

{% code lineNumbers="true" %}

```csharp
thumbnailSlider.SetMenuItem(Resource.Drawable.left_icon, ThumbnailSlider.PositionLeft);
```

{% endcode %}

## Thumbnail slider listeners

### Buttons listener

You can add a menu item clicked event listener by calling [`MenuItemClicked`](https://sdk.apryse.com/api/xamarinandroid/tools/api/pdftron.PDF.Controls.NativeThumbnailSlider.html#pdftron_PDF_Controls_NativeThumbnailSlider_MenuItemClicked) to be notified when one of the left or right buttons is clicked.

{% code lineNumbers="true" %}

```csharp
thumbnailSlider.MenuItemClicked += (sender, e) =>
{
    if (e.MenuItemPosition == ThumbnailSlider.PositionLeft)
    {
        // The left button was clicked.
    }
    else
    {
        // The right button was clicked.
    }
}
```

{% endcode %}

### Seekbar listener

You can set a thumbnail slider seekbar event listener by calling [`ThumbSliderStartTrackingTouch`](https://sdk.apryse.com/api/xamarinandroid/tools/api/pdftron.PDF.Controls.NativeThumbnailSlider.html#pdftron_PDF_Controls_NativeThumbnailSlider_ThumbSliderStartTrackingTouch) and [`ThumbSliderStopTrackingTouch`](https://sdk.apryse.com/api/xamarinandroid/tools/api/pdftron.PDF.Controls.NativeThumbnailSlider.html#pdftron_PDF_Controls_NativeThumbnailSlider_ThumbSliderStopTrackingTouch):

{% code lineNumbers="true" %}

```csharp
thumbnailSlider.ThumbSliderStartTrackingTouch += (sender, e) =>
{
    // Called when tracking on the seekbar has started
}
thumbnailSlider.ThumbSliderStopTrackingTouch += (sender, e) =>
{
    // Called when tracking on the seekbar has stopped
}
```

{% endcode %}

## Appearance style

### Customize slider colors

You can customize the color of the left and right menu buttons as well as the seekbar by setting a custom style to the `thumbnail_slider` attribute in your apps's theme. The custom style must extend `ThumbnailSliderStyle`. For example:

{% code lineNumbers="true" %}

```xml
<style name="PDFTronAppTheme" parent="PDFTronAppThemeBase"> <item name="colorPrimary">@color/app_color_primary_day</item> <item name="colorPrimaryDark">@color/app_color_primary_dark_day</item> <item name="colorAccent">@color/app_color_accent</item> <!-- Set your custom style in your app theme --> <item name="thumbnail_slider">@style/CustomThumbnailSliderStyle</item> </style>

<style name="CustomThumbnailSliderStyle" parent="ThumbnailSliderStyle"> <!-- Change the background color of the slider--> <item name="colorBackground">@android:color/red</item> <!-- Change the color of the seekbar and seekbar icon in the slider--> <item name="seekbarColor">@android:color/black</item> <!-- Change the color of the menu button left of the slider --> <item name="leftMenuItemColor">@android:color/black</item> <!-- Change the color of the menu button right of the slider --> <item name="rightMenuItemColor">@android:color/black</item> <!-- Change the description of the menu button left of the slider --> <item name="leftMenuItemContentDescription">"LeftDescription"</item> <!-- Change the color of the menu button right of the slider --> <item name="rightMenuItemContentDescription">"RightDescription"</item> <!-- Change the icon of the menu button left of the slider --> <item name="leftMenuItemDrawable">@drawable/ic_thumbnails_grid_black_24dp</item> <!-- Change the icon of the menu button right of the slider --> <item name="rightMenuItemDrawable">@drawable/ic_list_white_24dp</item> </style>
```

{% endcode %}

### Customize seekbar attributes

If you want to further customize the seekbar's layout attributes and appearance, such as padding and height, you can override the default seekbar style `Resource.Style.ThumbnailSliderStyle.Seekbar` by declaring the following in `Resources/Values/styles.xml`:

**Example**

For API < 21:

{% code lineNumbers="true" %}

```xml
<style name="ThumbnailSliderStyle.Seekbar" parent="Widget.AppCompat.SeekBar" > <!-- add paddingTop and paddingBottom for api < 21 here for avoiding seekbar becomes too thick--> <item name="android:paddingTop">16dp</item> <item name="android:paddingBottom">16dp</item> <item name="android:minHeight">2dp</item> <item name="android:maxHeight">2dp</item> <item name="android:layout_gravity">center</item> </style>
```

{% endcode %}

For API >= 21:

{% code lineNumbers="true" %}

```xml
<style name="ThumbnailSliderStyle.Seekbar" parent="Widget.AppCompat.SeekBar"> <item name="android:progressTint">?attr/colorPrimary</item> <item name="android:progressBackgroundTint">?attr/colorPrimary</item> <item name="android:colorControlActivated">?attr/colorPrimary</item> <item name="android:colorControlHighlight">?attr/colorPrimary</item> <item name="android:minHeight">2dp</item> <item name="android:maxHeight">2dp</item> <item name="android:layout_gravity">center</item> </style>
```

{% endcode %}

### Customize the thumb and progress bar

The seekbar progress bar drawable can be customized by overriding the `seek_track_material.xml` drawable file. Similarly, the seekbar thumbnail drawable can be changed by overriding the `seek_thumb.xml` drawable file. For reference, the source code for these drawables can be found in the `lib\src\PDFViewCtrlTools\res\drawable` folder of the SDK package.

## XML attributes

| Attribute                             | Description                                                                                                                               | Format    |
| ------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------- | --------- |
| `app:pdfviewctrlId`                   | Specifies the `PDFViewCtrl` view id                                                                                                       | Reference |
| `app:leftMenuItemContentDescription`  | Specifies the content description of left menu item.                                                                                      | String    |
| `app:rightMenuItemContentDescription` | Specifies the content description of right menu item.                                                                                     | String    |
| `app:leftMenuItemDrawable`            | Specifies left menu item drawable resource.                                                                                               | Reference |
| `app:rightMenuItemDrawable`           | Specifies right menu item drawable resource.                                                                                              | Reference |
| `app:colorBackground`                 | Specifies background color. Uses default system background color if not defined.                                                          | Color     |
| `app:seekbarColor`                    | Specifies seekbar progress bar and thumb color. Default value: `?attr/colorPrimary` in day mode and `@android:color/white` in night mode. | Color     |
| `app:leftMenuItemColor`               | Specifies left menu item color. Default value: `?attr/colorPrimary` in day mode and `@android:color/white` in night mode.                 | Color     |
| `app:rightMenuItemColor`              | Specifies right menu item color. Default value: `?attr/colorPrimary` in day mode and `@android:color/white` in night mode.                | Color     |
| `app:shadowEnabled`                   | Specifies whether the shadow will appear. Default value: `true`.                                                                          | Boolean   |
| {% endtab %}                          |                                                                                                                                           |           |

{% tab title="iOS" %}

## Adding PDF page slider in Xamarin.iOS

{% hint style="info" %}
**This tutorial only applies to Xamarin.iOS. See Xamarin.Android equivalent here .**
{% endhint %}

The [`PTThumbnailSliderViewController`](https://sdk.apryse.com/api/xamarinios/tools/api/pdftron.PDF.Controls.PTThumbnailSliderViewController.html) class allows the user to quickly navigate through a document. When using the slider control, a small page preview pop will be shown on top of the thumbnail slider.

Note: If you are using the new UI, we recommend the `PTDocumentSliderViewController` class, which displays a scroll indicator for the current scroll position and allows the user to quickly skip through pages.

![](https://653871032-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FgjsBtuYmcKhWOdM9VCg4%2Fuploads%2Fgit-blob-f9febe07a85d44675b5ad03e550640c736bf7123%2Fd737ad4d9851f59b5429599867cdb1e68b062fc8-750x615.png?alt=media)

*The thumbnail slider control is part of the Tools library, so make sure you have* [*added the Tools library to your project*](/xamarin/ui-customization/setup.md)*.*

## Show a thumbnail slider

To create and set up a thumbnail slider, supply a `PTPDFViewCtrl` instance to the `PTThumbnailSliderViewController` designated initializer:

{% code lineNumbers="true" %}

```csharp
var thumbnailSlider = new pdftron.PDF.Controls.PTThumbnailSliderViewController(mPdfViewCtrl);

AddChildViewController(thumbnailSlider);
View.AddSubview(thumbnailSlider.View);

thumbnailSlider.View.TranslatesAutoresizingMaskIntoConstraints = false;

NSLayoutConstraint.ActivateConstraints(new NSLayoutConstraint[] {
    thumbnailSlider.View.LeadingAnchor.ConstraintEqualTo(this.View.LeadingAnchor),
    thumbnailSlider.View.WidthAnchor.ConstraintEqualTo(this.View.WidthAnchor),
    thumbnailSlider.View.BottomAnchor.ConstraintEqualTo(this.View.BottomAnchor)
});
thumbnailSlider.DidMoveToParentViewController(this);
```

{% endcode %}

## Populate with thumbnail images

The thumbnail images shown in the thumbnail slider view controller are generated by the `GetThumbAsync:` method of the `PTPDFViewCtrl` class. When ready, the thumbnail images are provided to the `pdfviewCtrl`'s delegate via the `pdfViewCtrl:gotThumbAsync:thumbImage:` method.

In your class adopting the `PTPDFViewCtrlDelegate` protocol (usually the same view controller containing the thumbnail slider view controller), add the following:

{% code lineNumbers="true" %}

```csharp
mPdfViewCtrl.GotThumbAsync += (sender, e) =>
{
    if (e.Image == null)
    {
        return;
    }
    this.thumbnailSlider?.SetThumbnail(e.Image, e.Page_num);
};
```

{% endcode %}

## Customization

The [`PTThumbnailSliderViewController`](https://sdk.apryse.com/api/xamarinios/tools/api/pdftron.PDF.Controls.PTThumbnailSliderViewController.html) provides a flexible API for displaying buttons on either side of the slider control. This is possible with the following properties:

[`LeadingToolbarItem`](https://sdk.apryse.com/api/xamarinios/tools/api/pdftron.PDF.Controls.PTThumbnailSliderViewController.html#pdftron_PDF_Controls_PTThumbnailSliderViewController_LeadingToolbarItem) - a single `UIBarButtonItem` to the left of the slider.[`LeadingToolbarItems`](https://sdk.apryse.com/api/xamarinios/tools/api/pdftron.PDF.Controls.PTThumbnailSliderViewController.html#pdftron_PDF_Controls_PTThumbnailSliderViewController_LeadingToolbarItems) - an array of `UIBarButtonItem`s to the left of the slider.[`TrailingToolbarItem`](https://sdk.apryse.com/api/xamarinios/tools/api/pdftron.PDF.Controls.PTThumbnailSliderViewController.html#pdftron_PDF_Controls_PTThumbnailSliderViewController_TrailingToolbarItem) - a single `UIBarButtonItem` to the right of the slider.[`TrailingToolbarItems`](https://sdk.apryse.com/api/xamarinios/tools/api/pdftron.PDF.Controls.PTThumbnailSliderViewController.html#pdftron_PDF_Controls_PTThumbnailSliderViewController_TrailingToolbarItems) - an array of `UIBarButtonItem`s to the right of the slider.

It is also possible to remove these buttons by setting the appropriate property to nil.

For example, to show a button to present a [`PTThumbnailsViewController`](https://sdk.apryse.com/api/xamarinios/tools/api/pdftron.PDF.Controls.PTThumbnailsViewController.html) on the left of the slider, and a button to present a [`PTNavigationListsViewController`](https://sdk.apryse.com/api/xamarinios/tools/api/pdftron.PDF.Controls.PTNavigationListsViewController.html) on the right:

{% code lineNumbers="true" %}

```csharp
// add a custom UIBarButtonItem to the left of the thumbnail slider
thumbnailSlider.LeadingToolbarItem = new UIBarButtonItem(UIImage.FromFile("icon.png"), UIBarButtonItemStyle.Plain, (sender, e) => {
	// perform custom action
});

// add an array of UIBarButtonItems to the right of the slider
var button1 = new UIBarButtonItem(UIImage.FromFile("icon1.png"), UIBarButtonItemStyle.Plain, (sender, e) => {
    // perform custom action
});
var button2 = new UIBarButtonItem(UIImage.FromFile("icon2.png"), UIBarButtonItemStyle.Plain, (sender, e) => {
    // perform custom action
});
documentViewController.ThumbnailSliderController.TrailingToolbarItems = new UIBarButtonItem[] {button1, button2};

// remove the buttons from the left of the slider by setting the property to null
documentViewController.ThumbnailSliderController.LeadingToolbarItems = null;
```

{% endcode %}

## The thumbnail slider delegate

The `PTThumbnailSliderViewDelegate` protocol allows the adopting class (usually the containing view controller, as in this guide) to be notified when the user is actively using the thumbnail slider. The thumbnail slider already handles changing the current page in response to user actions, but the delegate methods can be used to hide or show other content as appropriate.
{% endtab %}
{% endtabs %}


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