# Template Preview

> Add a merge preview to a WPF template designer: a ToggleButton, DataSourceManager.Merge, MergeSettings, read-only EditMode and paging through records.

- **Product:** TX Text Control .NET for WPF
- **Section:** Documentation
- **Kind:** Topic
- **Path:** TX Text Control .NET for WPF > Mail Merge and Reporting > Template Preview
- **3205 words**
- **Web URL:** https://docs.textcontrol.com/tx-text-control-dotnet-wpf/mail-merge/template-preview/
- **LLMs URL:** https://docs.textcontrol.com/tx-text-control-dotnet-wpf/mail-merge/template-preview/llms.txt
- **LLMs-Full URL:** https://docs.textcontrol.com/tx-text-control-dotnet-wpf/mail-merge/template-preview/llms-full.txt

---

Designers of a template want to know what it produces before anyone merges real data: does the table grow, do empty lines disappear, are the prices formatted? A preview answers this in the editor itself. It merges the template in the WPF `TextControl` with the sample data of the **Reporting** tab, shows a few merged records one after the other and returns to the template when the designer is done. A toggle button and two buttons in XAML, plus some code behind, are all it takes.

The preview uses the data loaded into the tab, as in [Create a Template](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/getting-started/mail-merge/template/#load-the-sample-data-into-the-tab). Merging the real data is a separate step with `MailMerge`, shown in [Merge Data into Fields](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/getting-started/mail-merge/fields/llms-full.txt).

### How a Preview Works

The WPF **Reporting** tab has no preview button, but its [DataSourceManager](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-wpf/ribbonreportingtab/datasourcemanager-property/llms-full.txt) merges a template with the data it holds. [Merge](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/datasourcemanager/merge-method/llms-full.txt) takes the template as a byte array in the internal TX Text Control format and returns a list with one merged document per record, limited to a number of records you choose. A preview therefore:

1. saves the template from the editor into a byte array and keeps it,
2. merges the byte array and loads a merged record into the editor,
3. loads the kept template again when the designer returns to it.

The TX Words *Reporting* sample for WPF works this way. Its **Merge and Export** button asks for the number of records and the empty elements to remove in a **Merge Settings** dialog box of the sample:

![TX Text Control Words for WPF with an invoice template, the Reporting tab, the Merge Settings dialog box with the number of records, Merge all records, Merge into single document and check boxes for removing empty blocks, fields, lines, images and trailing whitespace, and the Field Navigation sidebar](https://docs.textcontrol.com/assets/img/tx-text-control-dotnet-wpf/reporting-field-navigation.de82662a.webp)

A **Results** tab then pages through the merged records, and its **Export Merge Result** dialog box saves them as files:

![TX Text Control Words for WPF with a merged invoice, the Results tab with the buttons Exit, First Record, Previous Record, Next Record, Last Record and Export Merge Result, and the Export Merge Result dialog box](https://docs.textcontrol.com/assets/img/tx-text-control-dotnet-wpf/merge-results-tab.51e568c9.webp)

The source code of the sample is in *%USERPROFILE%\\Documents\\TX Text Control 34.0.NET for WPF\\CSharp\\TX Words\\Reporting*.

### Add a Preview

The following code extends the window of [Create a Template](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/getting-started/mail-merge/template/llms-full.txt), which has a `RibbonReportingTab` named `ribbonReportingTab1` and a `TextControl` named `textControl1`. Add a toggle button and two buttons to the `DockPanel` of *MainWindow.xaml*, before the `TextControl` element:

```xml
<StackPanel DockPanel.Dock="Top" Orientation="Horizontal">
    <ToggleButton x:Name="previewToggle" Content="Preview"
                  Checked="previewToggle_Checked" Unchecked="previewToggle_Unchecked" />
    <Button x:Name="previousRecordButton" Content="Previous" Click="previousRecordButton_Click" />
    <Button x:Name="nextRecordButton" Content="Next" Click="nextRecordButton_Click" />
</StackPanel>
```

The handlers go into *MainWindow.xaml.cs*:

```csharp
using System.Collections.Generic;
using System.Windows;
using TXTextControl;
using TXTextControl.DocumentServer.DataSources;
```

```csharp
private byte[] template;
private IList<byte[]> previews;
private int previewIndex;

private void previewToggle_Checked(object sender, RoutedEventArgs e)
{
    DataSourceManager dataSourceManager = ribbonReportingTab1.DataSourceManager;

    if (!dataSourceManager.IsMergingPossible)
    {
        MessageBox.Show(this, "Load a data source into the Reporting tab first.");
        previewToggle.IsChecked = false;
        return;
    }

    // Keep the template to restore it later
    textControl1.Save(out template, BinaryStreamType.InternalUnicodeFormat);

    MergeSettings mergeSettings = new MergeSettings
    {
        RemoveEmptyFields = true,
        RemoveEmptyLines = false,
        RemoveEmptyImages = false
    };

    // Merge the first five records, one document each
    previews = dataSourceManager.Merge(template, 5, textControl1, mergeSettings);
    previewIndex = 0;

    ShowRecord();
    textControl1.EditMode = EditMode.ReadAndSelect;
}

private void previewToggle_Unchecked(object sender, RoutedEventArgs e)
{
    if (template == null)
    {
        return;
    }

    // Bring back the template and make it editable again
    textControl1.Load(template, BinaryStreamType.InternalUnicodeFormat);
    textControl1.EditMode = EditMode.Edit;
    template = null;
    previews = null;
    Title = "Template";
}

private void ShowRecord()
{
    textControl1.Load(previews[previewIndex], BinaryStreamType.InternalUnicodeFormat);
    Title = $"Preview: record {previewIndex + 1} of {previews.Count}";
}

private void nextRecordButton_Click(object sender, RoutedEventArgs e)
{
    if (previews != null && previewIndex < previews.Count - 1)
    {
        previewIndex++;
        ShowRecord();
    }
}

private void previousRecordButton_Click(object sender, RoutedEventArgs e)
{
    if (previews != null && previewIndex > 0)
    {
        previewIndex--;
        ShowRecord();
    }
}
```

The code works as follows:

- The `Checked` and `Unchecked` events of the `ToggleButton` switch between the preview and the template.
- [IsMergingPossible](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/datasourcemanager/ismergingpossible-property/llms-full.txt) is `false` while the requirements of `Merge` aren't met, for example before data is loaded. The toggle button is then reset.
- `textControl1.Save` writes the template with its fields and blocks into `template`, in `BinaryStreamType.InternalUnicodeFormat`.
- `Merge` merges at most five records into five documents. The `WPF.TextControl` is passed for licensing.
- [MergeSettings](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/mergesettings/llms-full.txt) control what the merge removes. [RemoveEmptyLines](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/mergesettings/removeemptylines-property/llms-full.txt) and [RemoveEmptyImages](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/mergesettings/removeemptyimages-property/llms-full.txt) are `true` by default here and `false` by default in `MailMerge`; the code sets both to `false`, so the preview looks like a merge with the default settings of `MailMerge`.
- [EditMode](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-wpf/textcontrol/editmode-property/llms-full.txt) set to `ReadAndSelect` keeps users from editing the preview, whose changes would be lost.
- `ShowRecord` loads one merged document and shows its number in the title of the window.

Press **F5**, load data into the Reporting tab and click **Preview**. The first record appears; **Next** and **Previous** page through the others, and a second click on **Preview** restores the template.

### Merge Settings

`MergeSettings` has these properties:

| Property | Default | What it does |
|---|---|---|
| [AsSingleDocument](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/mergesettings/assingledocument-property/llms-full.txt) | `false` | Combines the records into one document; each record starts on a new page after a section break |
| [RemoveEmptyBlocks](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/mergesettings/removeemptyblocks-property/llms-full.txt) | `true` | Removes the content of merge blocks without data |
| [RemoveEmptyFields](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/mergesettings/removeemptyfields-property/llms-full.txt) | `true` | Removes fields without data |
| [RemoveEmptyImages](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/mergesettings/removeemptyimages-property/llms-full.txt) | `true` | Removes images without merge data |
| [RemoveEmptyLines](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/mergesettings/removeemptylines-property/llms-full.txt) | `true` | Removes lines that are empty after the merge |
| [RemoveTrailingWhitespace](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/mergesettings/removetrailingwhitespace-property/llms-full.txt) | `true` | Removes trailing whitespace |

With `AsSingleDocument`, the returned list holds a single document with all records, which designers scroll through instead of paging. [MergeCulture](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/datasourcemanager/mergeculture-property/llms-full.txt) of the `DataSourceManager` sets the culture that formats numbers and dates; by default, it is the culture of the current thread.

### Find Fields Without Data in the Preview

During `Merge`, the `DataSourceManager` raises [FieldMerged](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/datasourcemanager/fieldmerged-event/llms-full.txt) and [DataRowMerged](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-documentserver-datasources/datasourcemanager/datarowmerged-event/llms-full.txt) with the same arguments as the events of `MailMerge`. A `FieldMerged` handler can collect the fields whose `Merged` property is `false` and show them beside the preview; [Template Design](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/mail-merge/template-design/#test-a-template) does the same with `MailMerge`.

### Preview With MailMerge

`DataSourceManager.Merge` uses the data the designer loaded into the tab. When the preview must use the data and settings of your real merge, merge with `MailMerge` in a `ServerTextControl` and load the result into the editor, as [Merge Data into Fields](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/getting-started/mail-merge/fields/llms-full.txt) does. The description of the TX Words sample also recommends `MailMerge` for merging real documents, and uses the `DataSourceManager` for its preview only.

### Next Steps

- [Reporting Ribbon and WPF Dialog Boxes](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/mail-merge/ribbon-dialogs/llms-full.txt): the tab whose data the preview merges.
- [Template Design](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/mail-merge/template-design/llms-full.txt): test templates before they are used.
- [Merge Events](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/mail-merge/events/llms-full.txt): follow a merge with events.

---

## Nearby

- **Previous:** [Reporting Ribbon and WPF Dialog Boxes](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/mail-merge/ribbon-dialogs/llms-full.txt)
- **Next:** [Merge Events](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/mail-merge/events/llms-full.txt)