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# Drop Site Example

The example shows how to distinguish the various MIME formats available in a drag and drop operation.

The Drop Site example accepts drops from other applications, and displays the MIME formats provided by the drag object.

There are two classes, `DropArea` and `DropSiteWindow`, and a `main()` function in this example. A `DropArea` object is instantiated in `DropSiteWindow`; a `DropSiteWindow` object is then invoked in the `main()` function.

## DropArea Class Definition

The `DropArea` class is a subclass of QLabel with a public slot, `clear()`, and a `changed()` signal. Missing snippet: draganddrop/dropsite/droparea.h. In addition, `DropArea` also contains a private instance of QLabel and reimplementations of four QWidget event handlers:

1. dragEnterEvent()
2. dragMoveEvent()
3. dragLeaveEvent()
4. dropEvent()

These event handlers are further explained in the implementation of the `DropArea` class. Missing snippet: draganddrop/dropsite/droparea.h.

## DropArea Class Implementation

In the `DropArea` constructor, we set the minimum size to 200x200 pixels, the frame style to both QFrame::Sunken and QFrame::StyledPanel, and we align its contents to the center. Missing snippet: draganddrop/dropsite/droparea.cpp. Also, we enable drop events in `DropArea` by setting the acceptDrops property to `true`. Then, we enable the autoFillBackground property and invoke the `clear()` function.

The dragEnterEvent() event handler is called when a drag is in progress and the mouse enters the `DropArea` object. For the `DropSite` example, when the mouse enters `DropArea`, we set its text to "<drop content>" and highlight its background. Missing snippet: draganddrop/dropsite/droparea.cpp. Then, we invoke acceptProposedAction() on `event`, setting the drop action to the one proposed. Lastly, we emit the `changed()` signal, with the data that was dropped and its MIME type information as a parameter.

For dragMoveEvent(), we just accept the proposed QDragMoveEvent object, `event`, with acceptProposedAction(). Missing snippet: draganddrop/dropsite/droparea.cpp. The `DropArea` class's implementation of dropEvent() extracts the `event`'s mime data and displays it accordingly. Missing snippet: draganddrop/dropsite/droparea.cpp. The `mimeData` object can contain one of the following objects: an image, HTML text, plain text, or a list of URLs. Missing snippet: draganddrop/dropsite/droparea.cpp.

- If `mimeData` contains an image, we display it in `DropArea` with setPixmap().
- If `mimeData` contains HTML, we display it with setText() and set `DropArea`'s text format as Qt::RichText.
- If `mimeData` contains plain text, we display it with setText() and set `DropArea`'s text format as Qt::PlainText. In the event that `mimeData` contains URLs, we iterate through the list of URLs to display them on individual lines.
- If `mimeData` contains other types of objects, we set `DropArea`'s text, with setText() to "Cannot display data" to inform the user.

We then set `DropArea`'s backgroundRole to QPalette::Dark and we accept `event`'s proposed action. Missing snippet: draganddrop/dropsite/droparea.cpp. The dragLeaveEvent() event handler is called when a drag is in progress and the mouse leaves the widget. Missing snippet: draganddrop/dropsite/droparea.cpp. For `DropArea`'s implementation, we clear invoke `clear()` and then accept the proposed event.

The `clear()` function sets the text in `DropArea` to "<drop content>" and sets the backgroundRole to QPalette::Dark. Lastly, it emits the `changed()` signal. Missing snippet: draganddrop/dropsite/droparea.cpp.

## DropSiteWindow Class Definition

The `DropSiteWindow` class contains a constructor and a public slot, `updateFormatsTable()`. Missing snippet: draganddrop/dropsite/dropsitewindow.h. The class also contains a private instance of `DropArea`, `dropArea`, QLabel, `abstractLabel`, QTableWidget, `formatsTable`, QDialogButtonBox, `buttonBox`, and two QPushButton objects, `clearButton` and `quitButton`.

## DropSiteWindow Class Implementation

In the constructor of `DropSiteWindow`, we instantiate `abstractLabel` and set its wordWrap property to `true`. We also call the adjustSize() function to adjust `abstractLabel`'s size according to its contents. Missing snippet: draganddrop/dropsite/dropsitewindow.cpp. Then we instantiate `dropArea` and connect its `changed()` signal to `DropSiteWindow`'s `updateFormatsTable()` slot. Missing snippet: draganddrop/dropsite/dropsitewindow.cpp. We now set up the QTableWidget object, `formatsTable`. Its horizontal header is set using a QStringList object, `labels`. The number of columms are set to two and the table is not editable. Also, the `formatTable`'s horizontal header is formatted to ensure that its second column stretches to occupy additional space available. Missing snippet: draganddrop/dropsite/dropsitewindow.cpp. Two QPushButton objects, `clearButton` and `quitButton`, are instantiated and added to `buttonBox` - a QDialogButtonBox object. We use QDialogButtonBox here to ensure that the push buttons are presented in a layout that conforms to the platform's style. Missing snippet: draganddrop/dropsite/dropsitewindow.cpp. The clicked() signals for `quitButton` and `clearButton` are connected to close() and `clear()`, respectively.

For the layout, we use a QVBoxLayout, `mainLayout`, to arrange our widgets vertically. We also set the window title to "Drop Site" and the minimum size to 350x500 pixels. Missing snippet: draganddrop/dropsite/dropsitewindow.cpp. We move on to the `updateFormatsTable()` function. This function updates the `formatsTable`, displaying the MIME formats of the object dropped onto the `DropArea` object. First, we set QTableWidget's rowCount property to 0. Then, we validate to ensure that the QMimeData object passed in is a valid object. Missing snippet: draganddrop/dropsite/dropsitewindow.cpp. Once we are sure that `mimeData` is valid, we iterate through its supported formats using the foreach keyword. This keyword has the following format:

            foreach(variable, container)

In our example, `format` is the `variable` and the `container` is a QStringList, obtained from `mimeData->formats()`.

Note: The formats() function returns a QStringList object, containing all the formats supported by the `mimeData`. Missing snippet: draganddrop/dropsite/dropsitewindow.cpp. Within each iteration, we create a QTableWidgetItem, `formatItem` and we set its flags to Qt::ItemIsEnabled, and its text alignment to Qt::AlignTop and Qt::AlignLeft.

A QString object, `text`, is customized to display data according to the contents of `format`. We invoke {QString}'s simplified() function on `text`, to obtain a string that has no additional space before, after or in between words. Missing snippet: draganddrop/dropsite/dropsitewindow.cpp. If `format` contains a list of URLs, we iterate through them, using spaces to separate them. On the other hand, if `format` contains an image, we display the data by converting the text to hexadecimal. Missing snippet: draganddrop/dropsite/dropsitewindow.cpp. Once `text` has been customized to contain the appropriate data, we insert both `format` and `text` into `formatsTable` with setItem(). Lastly, we invoke resizeColumnToContents() on `formatsTable`'s first column.

## The main() Function

Within the `main()` function, we instantiate `DropSiteWindow` and invoke its show() function. Missing snippet: draganddrop/dropsite/main.cpp.