通过反射读取R.drawable对应地图片资源id

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1.首先R文件是一个java类而drawable是其一个静态内部类其所有的字段都为静态字段对于静态字段通过反射读取时是不需要指定对象的所以 getInt(null)中的参数置空

protected int getDrawableId(String key) {      try {            String name = key;            Field field = R.drawable.class.getField(name);            return field.getInt(null);        } catch (SecurityException e) {        } catch (NoSuchFieldException e) {        } catch (IllegalAccessException e) {        }        return -1;    }

2,对于非静态字段我们是要指定对象参数的 like this

import java.lang.reflect.*;public class ClassDemo {   public int num = 123;   public static void main(String[] args) {     ClassDemo c = new ClassDemo();     Class cls = c.getClass();     System.out.println("Field =");     try {        // string field        Field sField = cls.getField("num");        int num1=0;        try {             num1=sField.getInt(c);        } catch (IllegalArgumentException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        }        System.out.println("Public field found: " + sField.toString()+"value="+num1);     }     catch(NoSuchFieldException e) {        System.out.println(e.toString());     }   }   public ClassDemo() {   }   public ClassDemo(int num) {             this.num = num;   }}

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