Android 资源名获取资源ID的两种实现方式－附带例子说明

获取资源文件,res目录下的资源时,id报空指针！！！如何解决？

之前一直纠结的问题，如何获取资源的id？？

在android中，我们经常使用资源文件的id来代替这个资源，如 R.drawable.*** ，

那怎样通过文件名得到这个资源的Id的，这里介绍两种方法：

一：通过  getIdentifier (String name, String defType, String defPackage)方法。

  这里有两种实现

1.name 用package:type/entry，那么后面两个参数可以为null.

2.name只写文件名，后面两参数分别为文件类型和包路径。

栗子来了。。。

package com.taobao.serv1;
import android.content.Context;
/**
 * Created by apple on 16/9/7.
 */
public class Utils  {

    public static int getResource(Context context, String name, String type) {
        try {
            String packageName = context.getPackageName();
            return context.getResources().getIdentifier(name, type, packageName);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return 0;
    }
}

使用举栗子：

Utils.getResource(context, "selectorDialog", "style") //style里的文件名称
Utils.getResource(context, "jxt_sdk_dialog_towebpage", "layout") //style里的文件名称里的文件名称
Utils.getResource(context, "jxt_sdk_dialog_towebpage_btn_ok", "id") //id里的文件名称

原来google已经提供了这个极好用的方法。。

源码：

   /**
     * Return a resource identifier for the given resource name.  A fully
     * qualified resource name is of the form "package:type/entry".  The first
     * two components (package and type) are optional if defType and
     * defPackage, respectively, are specified here.
     * 
     * <p>Note: use of this function is discouraged.  It is much more
     * efficient to retrieve resources by identifier than by name.
     * 
     * @param name The name of the desired resource.
     * @param defType Optional default resource type to find, if "type/" is
     *                not included in the name.  Can be null to require an
     *                explicit type.
     * @param defPackage Optional default package to find, if "package:" is
     *                   not included in the name.  Can be null to require an
     *                   explicit package.
     * 
     * @return int The associated resource identifier.  Returns 0 if no such
     *         resource was found.  (0 is not a valid resource ID.)
     */
    public int getIdentifier(String name, String defType, String defPackage) {
        if (name == null) {
            throw new NullPointerException("name is null");
        }
        try {
            return Integer.parseInt(name);
        } catch (Exception e) {
            // Ignore
        }
        return mAssets.getResourceIdentifier(name, defType, defPackage);
    }

二：通过反射机制： 没有验证（摘自网络）

给个demo:    drawable文件夹中有一bluetooth.png图片。

package com.shao.acts;  
  
import java.lang.reflect.Field;  
  
import android.app.Activity;  
import android.os.Bundle;  
  
public class GetResIdActivity extends Activity {  
    /** Called when the activity is first created. */  
    @Override  
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.main);  
          
        //方式一：  
        int resId1 = getResources().getIdentifier("bluetooth", "drawable", "com.shao.acts");  
        if(R.drawable.bluetooth==resId1){  
        System.out.println("TRUE");  
        }  
        //方式二：  
        int resId2 = getResources().getIdentifier("com.shao.acts:drawable/bluetooth", null, null);  
        if(R.drawable.bluetooth==resId2){  
           System.out.println("TRUE");  
        }  
        //方式三：  
        int resId3  = getImage("bluetooth");  
        if(R.drawable.bluetooth==resId3){  
            System.out.println("TRUE");  
         }  
    }  
    public static int getImage(String pic) {  
          if(pic==null||pic.trim().equals("")){  
           return R.drawable.icon;  
          }  
          Class draw = R.drawable.class;  
          try {  
           Field field = draw.getDeclaredField(pic);  
           return field.getInt(pic);  
          } catch (SecurityException e) {  
           return R.drawable.icon;  
          } catch (NoSuchFieldException e) {  
           return R.drawable.icon;  
          } catch (IllegalArgumentException e) {  
           return R.drawable.icon;  
          } catch (IllegalAccessException e) {  
           return R.drawable.icon;  
          }  
         }  
} 

输出都为true.不信可以试试，O(∩_∩)O~