[英]Gtk+ Callback functions and signals help
我從這里得到以下示例,該示例在“增加-減少”標題下顯示了此示例。
#include <gtk/gtk.h>
gint count = 0;
char buf[5];
void increase(GtkWidget *widget, gpointer label)
{
count++;
sprintf(buf, "%d", count);
gtk_label_set_text(label, buf);
}
void decrease(GtkWidget *widget, gpointer label)
{
count--;
sprintf(buf, "%d", count);
gtk_label_set_text(label, buf);
}
int main(int argc, char** argv) {
GtkWidget *label;
GtkWidget *window;
GtkWidget *frame;
GtkWidget *plus;
GtkWidget *minus;
gtk_init(&argc, &argv);
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 250, 180);
gtk_window_set_title(GTK_WINDOW(window), "+-");
frame = gtk_fixed_new();
gtk_container_add(GTK_CONTAINER(window), frame);
plus = gtk_button_new_with_label("+");
gtk_widget_set_size_request(plus, 80, 35);
gtk_fixed_put(GTK_FIXED(frame), plus, 50, 20);
minus = gtk_button_new_with_label("-");
gtk_widget_set_size_request(minus, 80, 35);
gtk_fixed_put(GTK_FIXED(frame), minus, 50, 80);
label = gtk_label_new("0");
gtk_fixed_put(GTK_FIXED(frame), label, 190, 58);
gtk_widget_show_all(window);
g_signal_connect(window, "destroy",
G_CALLBACK (gtk_main_quit), NULL);
g_signal_connect(plus, "clicked",
G_CALLBACK(increase), label);
g_signal_connect(minus, "clicked",
G_CALLBACK(decrease), label);
gtk_main();
return 0;
}
我想知道的是g_signal_connect(plus, "clicked",G_CALLBACK(increase), label);
函數將“標簽”發送到函數void increase(GtkWidget *widget, gpointer label)
,其中其參數為void increase(GtkWidget *widget, gpointer label)
。 現在,在遞增函數中, gtk_label_set_text()
函數需要將數據類型GtkLabel
作為其第一個參數,但我只看到一個GtkWidget
變量和一個空指針label
作為遞增函數的參數。 如果是這樣,gtk_label_set_text()如何工作?
在C(但不是 C ++)中,可以將void*
隱式轉換為指向任何其他類型的指針。 在使用malloc
分配內存時,這很常見,這會返回void*
:
int *myIntArray = malloc(10 * sizeof(int)); // allocate array of 10 ints
您的代碼只是通過參數傳遞來完成相同的工作:
void gtk_label_set_text(GtkLabel *label, const char *text);
void *label = ...;
gtk_label_set_text(label, "some string"); // label is implicitly cast from
// void* to GtkLabel*
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