来源

我是在看Android10原生代码，绘制状态栏蓝牙电量相关类中第一次看到R.fraction的，如类BatteryMeterDrawable

<fraction name="battery_button_height_fraction">10%</fraction>

mButtonHeightFraction = context.getResources().getFraction(
                R.fraction.bt_battery_button_height_fraction, 1, 1);

方法解释

public float getFraction(@FractionRes int id, int base, int pbase) 
源码中方法解释如下：
Retrieve a fractional unit for a particular resource ID.
Params:
id – The desired resource identifier, as generated by the aapt tool. This integer encodes the package, type, and resource entry. The value 0 is an invalid identifier. base – The base value of this fraction. In other words, a standard fraction is multiplied by this value. pbase – The parent base value of this fraction. In other words, a parent fraction (nn%p) is multiplied by this value.
Returns:
Attribute fractional value multiplied by the appropriate base value.
Throws:
Resources.NotFoundException – Throws NotFoundException if the given ID does not exist.

用处

我自己没用过，待补充

测试

分别测试fraction的两种声明：有p的跟没p的

<item name="fraction" type="fraction">30%</item>
<item name="fraction" type="fraction">30%p</item>

测试没p的：

测试案例1：保持第三个参数不变

测试：

        //<item name="fraction" type="fraction">30%</item>float fraction1 = this.getResources().getFraction(R.fraction.fraction, 1, 1);float fraction2 = this.getResources().getFraction(R.fraction.fraction, 2, 1);float fraction3 = this.getResources().getFraction(R.fraction.fraction, 3, 1);float fraction4 = this.getResources().getFraction(R.fraction.fraction, 4, 1);

结果：

分析：

都是30%乘以第二个参数(base)

 测试案例1：第三个参数改变

 测试：

        //<item name="fraction" type="fraction">30%</item>float fraction1 = this.getResources().getFraction(R.fraction.fraction, 1, 2);float fraction2 = this.getResources().getFraction(R.fraction.fraction, 1, 3);float fraction3 = this.getResources().getFraction(R.fraction.fraction, 2, 2);float fraction4 = this.getResources().getFraction(R.fraction.fraction, 2, 3);

结果：

分析：

都是30%乘以第二个参数(base)

 总结以上两个测试案例可知：在没p的情况下，getFraction方法返回的结果就是乘以第二个参数；

测试有p的：

 测试：

        //<item name="fraction" type="fraction">30%p</item>float fraction1 = this.getResources().getFraction(R.fraction.fraction, 1, 2);float fraction2 = this.getResources().getFraction(R.fraction.fraction, 1, 3);float fraction3 = this.getResources().getFraction(R.fraction.fraction, 2, 2);float fraction4 = this.getResources().getFraction(R.fraction.fraction, 2, 3);

结果：

分析：

都是30%乘以第三个参数(pbase)