在Android代码中创建环形

Question

我有以下形状XML:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:a="http://schemas.android.com/apk/res/android"
       a:shape="ring"
       a:innerRadiusRatio="3"
       a:thicknessRatio="8"
       a:useLevel="false">

    <!-- some other stuff goes here -->

    </gradient>
</shape>

我想用代码来创建这个形状,因为有些东西需要在我做之前动态计算,所以静态预定义布局不会削减它.

我是Android的新手,无法弄清楚XML如何转换为代码,并且没有继承自Shape的RingShape类.

除了回答这个问题之外,如果有一个指南可以详细说明XML和Java代码之间的关系以及如何处理XML以便最终在屏幕上显示,我也会感谢链接.谢谢.

Answer 1

鲁本已经指出了最有用的观察,所以我只关注故事的实施方面.使用反射的多种方法可能会为您提供所需的内容.

第一个是(ab)使用带有GradientState引用的私有GradientDrawable构造函数.不幸的是,后者是包含可见性的最终子类,因此您无法轻松访问它.为了使用它,您需要进一步深入使用反射或将其功能模仿到您自己的代码中.

第二种方法是使用反射来获取私有成员变量mGradientState,幸运的是它有一个getter形式getConstantState().这将为您提供ConstantState,它在运行时实际上是一个GradientState,因此我们可以使用反射来访问其成员并在运行时更改它们.

为了支持上述语句,这里有一个基本的实现,可以从代码中创建一个环形drawable:

RingDrawable.java

public class RingDrawable extends GradientDrawable {

    private Class<?> mGradientState;

    public RingDrawable() {
        this(Orientation.TOP_BOTTOM, null);
    }

    public RingDrawable(int innerRadius, int thickness, float innerRadiusRatio, float thicknessRatio) {
        this(Orientation.TOP_BOTTOM, null, innerRadius, thickness, innerRadiusRatio, thicknessRatio);
    }

    public RingDrawable(GradientDrawable.Orientation orientation, int[] colors) {
        super(orientation, colors);
        setShape(RING);
    }

    public RingDrawable(GradientDrawable.Orientation orientation, int[] colors, int innerRadius, int thickness, float innerRadiusRatio, float thicknessRatio) {
        this(orientation, colors);
        try {
            setInnerRadius(innerRadius);
            setThickness(thickness);
            setInnerRadiusRatio(innerRadiusRatio);
            setThicknessRatio(thicknessRatio);
        } catch (Exception e) {
            // fail silently - change to your own liking
            e.printStackTrace();
        }
    }

    public void setInnerRadius(int radius) throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
        if (mGradientState == null) mGradientState = resolveGradientState();
        Field innerRadius = resolveField(mGradientState, "mInnerRadius");
        innerRadius.setInt(getConstantState(), radius);
    }       

    public void setThickness(int thicknessValue) throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
        if (mGradientState == null) mGradientState = resolveGradientState();
        Field thickness = resolveField(mGradientState, "mThickness");
        thickness.setInt(getConstantState(), thicknessValue);
    }

    public void setInnerRadiusRatio(float ratio) throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
        if (mGradientState == null) mGradientState = resolveGradientState();
        Field innerRadiusRatio = resolveField(mGradientState, "mInnerRadiusRatio");
        innerRadiusRatio.setFloat(getConstantState(), ratio);
    }

    public void setThicknessRatio(float ratio) throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
        if (mGradientState == null) mGradientState = resolveGradientState();
        Field thicknessRatio = resolveField(mGradientState, "mThicknessRatio");
        thicknessRatio.setFloat(getConstantState(), ratio);
    }

    private Class<?> resolveGradientState() {
        Class<?>[] classes = GradientDrawable.class.getDeclaredClasses();
        for (Class<?> singleClass : classes) {
            if (singleClass.getSimpleName().equals("GradientState")) return singleClass;
        }
        throw new RuntimeException("GradientState could not be found in current GradientDrawable implementation");
    }

    private Field resolveField(Class<?> source, String fieldName) throws SecurityException, NoSuchFieldException {
        Field field = source.getDeclaredField(fieldName);
        field.setAccessible(true);
        return field;
    }

}

以上可以按如下方式用于从代码创建RingDrawable并将其显示在标准ImageView中.

ImageView target = (ImageView) findViewById(R.id.imageview);
RingDrawable ring = new RingDrawable(10, 20, 0, 0);
ring.setColor(Color.BLUE);
target.setImageDrawable(ring);

这将在ImageView中显示一个简单的不透明蓝色环(内部半径为10个单位,厚度为20个单位).您需要确保不将ImageView的宽度和高度设置为wrap_content,除非您添加ring.setSize(width, height)上面的代码以便显示它.

希望这可以帮助你以任何方式.

Answer 2

戒指和其他形状GradientDrawables.

如果查看GradientDrawable 的源代码,您会发现某些属性(如innerRadius)只能通过XML定义......它们不会通过访问器方法公开.相关状态对于类来说也是无用的,因此子类化也没有帮助.