Expression Blend(10)- 使用CallMethodAction Behavior

在Expression Blend(5)–自製Silverlight撥放程式範例中，我們利用Button的事件處理常式來叫用MediaElement 的Play、Pause、Stop方法撥放影片。在這個例子中，不撰寫Button的事件處理常式來撥放影片檔，改用CallMethodAction Behavior來達到這個目地。

例如目前Silverlight專案中，MainPage.xaml包含一個MediaElement 與3個Button

<UserControl
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
    xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
    x:Name="userControl" mc:Ignorable="d"
    x:Class="MyPlayer.MainPage"
    Width="640" Height="480">

    <Grid x:Name="LayoutRoot" Background="White">
        <MediaElement x:Name="Wildlife_wmv"
                      Margin="64,8,256,232"
                      Source="/Wildlife.wmv"
                      Stretch="Fill" Width="320" Height="240"
                      d:LayoutOverrides="HorizontalAlignment" AutoPlay="False">
       
        </MediaElement>
        <Button x:Name="btnPlay" Content="Play" HorizontalAlignment="Left"
                Height="40" Margin="118,0,0,168" VerticalAlignment="Bottom"
                Width="54" />
        <Button x:Name="btnPause" Content="Pause" Height="40"
                Margin="189,0,0,168" VerticalAlignment="Bottom"
                HorizontalAlignment="Left" Width="54"/>
        <Button x:Name="btnStop" Content="Stop" HorizontalAlignment="Left"
                Height="40" Margin="264,0,0,168" VerticalAlignment="Bottom"
                Width="54" />
    </Grid>
</UserControl>

MainPage.xaml.cs檔案包含程式如下:

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace MyPlayer {
    public partial class MainPage : UserControl {
        public MainPage ( ) {
            InitializeComponent ( );
        }
        public void Play ( ) {
            Wildlife_wmv.Play ( );
        }
        public void Pause ( ) {
            Wildlife_wmv.Pause ( );
        }
        public void Stop ( ) {
            Wildlife_wmv.Stop ( );
        }
    }
}

CallMethodAction Behavior是一個Conditional Behavior，這個Behavior會根據Trigger叫用Target Object的方法。Target Object的方法必須宣告為public，而且不可以有回傳值，也不能接收任何參數。

以下是使用CallMethodAction Behavior步驟

• Asserts-> Behaviors->CallMethodAction，將CallMethodAction Behavior拖曳到設計畫面MediaElement上方放開

• 設定CallMethodAction 的Trigger，點選SourceObject後方的Artboard element picker，拖曳到Play Button上點一下。

• EventName設Click

• 拖曳Common Properties->TargetObject到User Control (因為要叫用定義在User Control中的Play方法)

• 設MethodName為Play

• 目前您的MediaElement XAML看起來如下

<MediaElement x:Name="Wildlife_wmv" Margin="64,8,256,232" Source="/Wildlife.wmv" Stretch="Fill" Width="320" Height="240" d:LayoutOverrides="HorizontalAlignment" AutoPlay="False">
            <i:Interaction.Triggers>
                <i:EventTrigger SourceObject="{Binding ElementName=btnPlay}" EventName="Click">
                    <ei:CallMethodAction MethodName="Play" TargetObject="{Binding ElementName=userControl}"/>
                </i:EventTrigger>
            </i:Interaction.Triggers>       
        </MediaElement>

 

• 重複以上步驟加入CallMethodAction ，讓Pause、Stop按鈕能夠呼叫Pause與Stop方法。

 

• 按F5執行，你可以利用按鈕來控制撥放