当ToString（）有协作对象时，为什么WPF数据绑定不会显示文本？ [英] Why won't WPF databindings show text when ToString() has a collaborating object?

问题描述

以一种简单的形式，我绑定到一些不同的对象 - 一些在列表框中;一些在文本块中。

In a simple form, I bind to a number of different objects -- some go in listboxes; some in textblocks.

这些对象中有几个对象在执行 ToString（）方法时调用的协作对象它的工作 - 通常是某种格式化程序。

A couple of these objects have collaborating objects upon which the ToString() method calls when doing its work -- typically a formatter of some kind.

当我浏览代码时，我看到当数据绑定正在设置时，

When I step through the code I see that when the databinding is being set up,

1. ToString（）被称为


2. 协作对象不 null 并在调试器中检查时返回预期结果


3. ，对象从 ToString返回预期结果）

1. ToString() is called
2. the collaborating object is not null and returns the expected result
3. when inspected in the debugger, the objects return the expected result from ToString()

但是文字不

我看到的唯一常见的线程是使用协作对象，而显示为预期的其他绑定只能从属性和方法工作的包含对象。

The only common thread I see is that these use a collaborating object, whereas the other bindings that show up as expected simply work from properties and methods of the containing object.

如果这是令人困惑的，这里是代码中的要点：

If this is confusing, here is the gist in code:

public class ThisThingWorks
{
    private SomeObject some_object;

    public ThisThingWorks(SomeObject s) { some_object = s; }

    public override string ToString() { return some_object.name; }
}

public class ThisDoesntWork
{
    private Formatter formatter;
    private SomeObject some_object;

    public ThisDoesntWork(SomeObject o, Formatter f) 
    {
        formatter = f; 
        some_object = o;
    }

    public override string ToString()
    {
        return formatter.Format(some_object.name);
    }
}

再次让我重申 - $ $ c> ToString（）方法在每个其他上下文中工作 - 但是当我绑定到WPF中的对象并希望显示

Again, let me reiterate -- the ToString() method works in every other context -- but when I bind to the object in WPF and expect it to display the result of ToString(), I get nothing.

该问题似乎是我在 TextBlock 绑定中看到的错误行为。如果我将 Text 属性绑定到声明为接口类型的 DataContext 的属性， ToString（）从未被调用。如果我将属性声明更改为接口的实现，它将按预期工作。将 Content 属性绑定到 DataContext Label c $ c>属性被声明为实现或接口。

The issue seems to be what I see as a buggy behaviour in the TextBlock binding. If I bind the Text property to a property of the DataContext that is declared as an interface type, ToString() is never called. If I change the property declaration to an implementation of the interface, it works as expected. Other controls, like Label work fine when binding the Content property to a DataContext property declared as either the implementation or the interface.

因为这是远离这个问题的标题和内容，我创建了一个新的问题在这里： WPF绑定行为不同于bound属性被声明为接口vs类类型？

Because this is so far removed from the title and content of this question, I've created a new question here: WPF binding behaviour different when bound property is declared as interface vs class type?

更改了标题： WPF绑定行为是不同的

推荐答案

尝试这些简单的更改：

首先使用此版本的方法：

First test your program with this version of the method:

public override string ToString()
{
    return "This method's really being called."
}

如果在UI中实际显示内容，现在尝试此版本： p>

If that actually displays something in the UI, now try this version:

public override string ToString()
{
    Console.WriteLine(
       string.Format("some_object.name = {0}, formatter.Format(some_object.name) = {1}",
          some_object.name,
          formatter.Format(some_object.name));
    return formatter.Format(some_object.name);
}

如果这不引导你弄清楚是什么错误，我会非常惊讶。

If this doesn't lead you to figure out what's really wrong, I'll be extremely surprised.

这篇关于当ToString（）有协作对象时，为什么WPF数据绑定不会显示文本？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！