IOS development _ iPhone development _ How to Implement the drop-down list on the iPhone interface

The Code is as follows:

# Import <uikit/uikit. h>
@ Interface dropdownlist: uiview <uitableviewdelegate, uitableviewdatasource> {
Uitextfield * textfield; // text input box
Nsarray * List; // drop-down list data
Bool showlist; // whether to display the drop-down list
Uitableview * listview; // drop-down list
Cgrect oldframe, newframe; // The rectangle of the entire control (including before and after the drop-down)
Uicolor * linecolor, * listbgcolor; // The border color and background color of the drop-down box
Cgfloat linewidth; // The Border width of the drop-down box.
Uitextborderstyle borderstyle; // text box border Style
}
@ Property (nonatomic, retain) uitextfield * textfield;
@ Property (nonatomic, retain) nsarray * List;
@ Property (nonatomic, retain) uitableview * listview;
@ Property (nonatomic, retain) uicolor * linecolor, * listbgcolor;
@ Property (nonatomic, assign) uitextborderstyle borderstyle;
-(Void) drawview;
-(Void) setshowlist :( bool) B;
@ End
# Import "dropdownlist. H"
@ Implementation dropdownlist
@ Synthesize textfield, list, listview, linecolor, listbgcolor, borderstyle;
-(ID) initwithframe :( cgrect) frame {

If (Self = [Super initwithframe: frame]) {
// Data in the default drop-down list
List = [[nsarray alloc] initwithobjects: @ "1", @ "2", @ "3", @ "4", nil];

Borderstyle = uitextborderstyleroundedrect;

Showlist = no; // the drop-down list is not displayed by default.
Oldframe = frame; // initial size of the widget when no pull-down is performed
// When the drop-down box is displayed, the control size is calculated.
Newframe = cgrectmake (frame. Origin. X, frame. Origin. Y, frame. Size. Width, frame. Size. Height * 5 );

Linecolor = [uicolor lightgraycolor]; // the border line of the default list is gray.
Listbgcolor = [uicolor whitecolor]; // the background color of the default list box is white.
Linewidth = 1; // The Border width of the default list is 1.

// Set the background color to transparent, otherwise there will be a Black edge
Self. backgroundcolor = [uicolor clearcolor];
[Self drawview]; // call a method to draw controls

}
Returnself;
}
-(Void) drawview {
// Text box
Textfield = [[uitextfield alloc]
Initwithframe: cgrectmake (0, 0,
Oldframe. Size. Width,
Oldframe. Size. Height)];
Textfield. borderstyle = borderstyle; // you can specify the border style of the text box.
[Self addsubview: textfield];
[Textfield addtarget: Self action: @ selector (dropdown) forcontrolevents: uicontroleventalltouchevents];

// Drop-down list
Listview = [[uitableview alloc] initwithframe:
Cgrectmake (linewidth, oldframe. Size. height + linewidth,
Oldframe. Size. Width-linewidth * 2,
Oldframe. Size. Height * 4-linewidth * 2)];
Listview. datasource = self;
Listview. Delegate = self;
Listview. backgroundcolor = listbgcolor;
Listview. separatorcolor = linecolor;
Listview. Hidden =! Showlist; // The listview is hidden at the beginning, and then displayed or hidden based on the value of showlist.

[Self addsubview: listview];
[Listview release];
}
-(Void) dropdown {
[Textfield resignfirstresponder];
If (showlist) {// If the drop-down box is displayed, nothing will be done
Return;
} Else {// If the drop-down list is not displayed
// Put the dropdownlist in front to prevent the drop-down box from being hidden by other controls

[Self. superview bringsubviewtofront: Self];
[Self setshowlist: Yes]; // display the drop-down list
}
}
# Pragma mark listviewdatasource method and delegate Method
-(Nsinteger) tableview :( uitableview *) Table numberofrowsinsection :( nsinteger) Section {
Return list. count;
}
-(Uitableviewcell *) tableview :( uitableview *) tableview cellforrowatindexpath :( nsindexpath *) indexpath {
Static nsstring * cellid = @ "listviewid ";
Uitableviewcell * cell = [tableview dequeuereusablecellwithidentifier: cellid];
If (cell = nil ){
Cell = [[[uitableviewcell alloc] initwithstyle: uitableviewcellstyledefault
Reuseidentifier: cellid] autorelease];
}
// Text tag
Cell. textlabel. Text = (nsstring *) [list objectatindex: indexpath. Row];
Cell. textlabel. font = textfield. Font;

Cell. selectionstyle = uitableviewcellselectionstylegray;
Return cell;
}
-(Cgfloat) tableview :( uitableview *) tableview heightforrowatindexpath :( nsindexpath *) indexpath {
Return oldframe. Size. height;
}
// When selecting a row from the drop-down list, set the value in the text box to hide the drop-down list
-(Void) tableview :( uitableview *) tableviewdidselectrowatindexpath :( nsindexpath *) indexpath {
// Nslog (@ "select ");
Textfield. Text = (nsstring *) [list objectatindex: indexpath. Row];
// Nslog (@ "textfield. Text = % @", textfield. Text );
[Self setshowlist: No];
}
-(Bool) showlist {// setshowlist: No indicates hiding, and setshowlist: Yes indicates displaying
Return showlist;
}
-(Void) setshowlist :( bool) B {
Showlist = B;
Nslog (@ "showlist is set ");
If (showlist ){
Self. Frame = newframe;
} Else {
Self. Frame = oldframe;
}
Listview. Hidden =! B;
}
/*

// Only override drawrect: If you perform custom drawing.
// An empty implementation adversely affects performance during animation.
-(Void) drawrect :( cgrect) rect {
// Drawing code.
}
*/
-(Void) dealloc {
[Super dealloc];
}
@ End