Question

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
             prism:ViewModelLocator.AutowireViewModel="True"
             x:Class="VFood.Views.EntregadorEdit"
             Title="{Binding Title}">

    <ContentPage.ToolbarItems>
        <OnPlatform x:TypeArguments="ToolbarItem">
            <OnPlatform.iOS>
                <ToolbarItem x:Name="SalvarItemIOS" Name="Done" Command="{Binding SalvarCommand}" Order="Primary" Priority="0"/>
                <ToolbarItem x:Name="RemoveItemIOS" Name="Trash" Command="{Binding RemoveCommand}" Order="Primary" Priority="1"/>
            </OnPlatform.iOS>
            <OnPlatform.Android>
                <ToolbarItem x:Name="SalvarItemDroid" Icon="ic_check" Command="{Binding SalvarCommand}" Order="Primary" Priority="0"/>
                <ToolbarItem x:Name="RemoveItemDroid" Icon="ic_delete" Command="{Binding RemoveCommand}" Order="Primary"  Priority="1"/>
            </OnPlatform.Android>
        </OnPlatform>
    </ContentPage.ToolbarItems>

    <ContentPage.Content>
        <StackLayout Spacing="8">
            <StackLayout.Padding>
                <OnPlatform x:TypeArguments="Thickness"  Android="16,16,16,16" iOS="10,10,10,10"/>
            </StackLayout.Padding>
            <Entry Placeholder="Nome" Text="{Binding Entregador.Nome}"/>
            <Entry Placeholder="Telefone" Text="{Binding Entregador.Telefone}" Keyboard="Telephone" />
        </StackLayout>
    </ContentPage.Content>

</ContentPage>

假设我有一个这样的代码。在数组的每个元素中，都有一个具有唯一编号<?xml version="1.0" encoding="utf-8" ?> <ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms" prism:ViewModelLocator.AutowireViewModel="True" x:Class="VFood.Views.EntregadorEdit" Title="{Binding Title}"> <ContentPage.ToolbarItems> <OnPlatform x:TypeArguments="ToolbarItem"> <OnPlatform.iOS>  <ToolbarItem x:Name="RemoveItemIOS" Name="Trash" Command="{Binding RemoveCommand}" Order="Primary" Priority="1"/> </OnPlatform.iOS> <OnPlatform.Android>  <ToolbarItem x:Name="RemoveItemDroid" Icon="ic_delete" Command="{Binding RemoveCommand}" Order="Primary" Priority="1"/> </OnPlatform.Android> </OnPlatform> </ContentPage.ToolbarItems> <ContentPage.Content> <StackLayout Spacing="8"> <StackLayout.Padding> <OnPlatform x:TypeArguments="Thickness" Android="16,16,16,16" iOS="10,10,10,10"/> </StackLayout.Padding> <Entry Placeholder="Nome" Text="{Binding Entregador.Nome}"/> <Entry Placeholder="Telefone" Text="{Binding Entregador.Telefone}" Keyboard="Telephone" /> </StackLayout> </ContentPage.Content> </ContentPage>的变量。现在，我想使用这个数字来访问整个元素（并可能操纵它的其他变量）。我怎么能这样做？

Answer 1

在数组的每个元素中，都有一个唯一的变量号码(bar)。

由于您可以控制您的唯一键，因此可以很容易地实现这一点如果您按照排序顺序排列数组，则可以使用C库函数bsearch进行快速查找。

（注意：请在代码中初始化int var;。）

现在我想使用这个数字来访问整个元素（和也许操纵它的其他变量）

这可以像为函数get_foo指定键一样简单：

Foo *obj =  get_foo(3);

简单示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define ARRAY_SIZE 5
typedef struct Foo Foo;

struct Foo{
    int bar;  // key
    int var2; // etc...
    int var3; // etc...
};

Foo array[ARRAY_SIZE];

static int compare_keys(const void *va, const void *vb) {
    const Foo *a = va, *b = vb;
    return (a->bar -  b->bar);
}

Foo * get_foo(int key) {
    Foo *foo = bsearch(&key, array, sizeof array / sizeof array[0],
        sizeof array[0], compare_keys);
    return foo; 
}

int main(void){
    int var = 0;

    while(var < ARRAY_SIZE)
    {
        array[var].bar =    var;     // an unique key number 
        array[var].var2 = 2*var;     // some data
        array[var].var3 = 3*var;     // some data
        var++;
    }

    // The array of structures should be sorted by the value of the unique key 
    // verification that we can look up all the valid keys.
    for (int i = 0; i < sizeof array / sizeof array[0]; ++i) {
        Foo * v = get_foo(array[i].bar);

        if(v)
            printf("key: %3d ->  values:  %2d,  %3d\n", array[i].bar, v->var2, v->var3 );
        else
           printf("Key not found %2d \n", array[i].bar); 
    } 

    // finding a particular object is simple:
    printf("\nFind object for key = %2d \n", 3); 
    Foo *obj =  get_foo(3);
    if(obj)
        printf("key: %3d ->  values:  %2d,  %3d\n", 3, obj->var2, obj->var3 );

    return 0;
}

测试：

key:   0 ->  values:   0,    0                                                                                                                 
key:   1 ->  values:   2,    3                                                                                                                 
key:   2 ->  values:   4,    6                                                                                                                 
key:   3 ->  values:   6,    9                                                                                                                 
key:   4 ->  values:   8,   12                                                                                                                 

Find object for key =  3                                                                                                                       
key:   3 ->  values:   6,    9

使用存储在其结构中的变量访问数组元素

1 个答案: