如何更改图层列表可绘制对象?

问题描述

尝试学习一些新事物并且无法弄清楚这一点，我们将不胜感激.给出以下简单的代码，这些代码可以从Google文档中找到:

Trying to learn some new things and can't figure this one out, any help is appreciated. Given this simple code which is right from Google's documentation:

layers.xml:

layers.xml:

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@+id/first_image">
      <bitmap android:src="@drawable/android_red"
        android:gravity="center" />
    </item>
    <item android:id="@+id/second_image" android:top="10dp" android:left="10dp">
      <bitmap android:src="@drawable/android_green"
        android:gravity="center" />
    </item>
    <item android:id="@+id/third_image" android:top="20dp" android:left="20dp">
      <bitmap android:src="@drawable/android_blue"
        android:gravity="center" />
    </item>
</layer-list>

和main.xml:

<ImageView
    android:id="@+myImageView"
    android:layout_height="wrap_content"
    android:layout_width="wrap_content"
    android:src="@drawable/layers" />

问题:如何以编程方式引用图层列表中的一个可绘制对象，以便可以将其更改为其他可绘制对象?

Question: How do I programmatically reference one of the drawables in the layer-list so I can change it to a different drawable?

谢谢.

所以现在我有了新的drawable，我想在变量myImage中交换对吗?现在如何将其放入图层列表?我假设我使用findDrawableByLayerId和setDrawableByLayerId，但是究竟如何?否则我可能做错了！救命！

So now I have my new drawable that I want to swap in in variable myImage correct? Now how do I get that into the layer-list? I assume I use findDrawableByLayerId and setDrawableByLayerId, but how exactly? Or I could be doing it completely wrong! Help!

我要做什么?更改显示的绘图.例如，假设我有另一个名为"android_purple"的可绘制对象，如何在上面的层列表示例中将其切换为"android_green"可绘制对象?

What am I trying to do? Change the drawable that's displayed. For example suppose I had another drawable called "android_purple", how would I switch it in for the "android_green" drawable in the layer-list example above?

据我所知，这是到目前为止的代码(不起作用起作用，出现setDrawableByLayerId未定义的错误):

With my limited knowledge here is my code so far (which does not work, I get error that setDrawableByLayerId is undefined):

Resources res = getApplicationContext().getResources();
BitmapDrawable newImage = (BitmapDrawable) res.getDrawable(R.drawable.android_purple); //Get replacement image, can't use LayerDrawable or get error.
boolean layer_drawable_changed = (setDrawableByLayerId((R.id.second_image), newImage)); //Set new drawable? Error on this line.

推荐答案

这是我会尝试的:

步骤1:将android:id属性放在<item>元素上，如图所示在文档中

Step #1: Put android:id attributes on the <item> elements as illustrated in the documentation

步骤2:将getDrawable()结果转换为 LayerDrawable

Step #2: Cast the getDrawable() result to a LayerDrawable

步骤3:如果您不想使用Drawable影响其他任何人，请致电mutate()(可能是可选的)

Step #3: Call mutate() if you do not want to affect anyone else using the Drawable (may be optional)

第4步:调用setDrawableByLayerId()设置/替换给定层ID的Drawable

Step #4: Call setDrawableByLayerId() to set/replace a Drawable for a given layer ID

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