【Android 应用开发】Android开发技巧--Application, ListView排列,格式化浮点数,string.xml占位符,动态引用图片

public class MyApplication extends Application {
	/*
	 * 单例模式 : 私有 静态 本类的对象
	 */
	private static MyApplication mApplication;
	
	/*
	 * 单例模式 : 构造方法 , 注意 : Application的构造方法必须是public的
	 */
	public ReceiverApplication(){
		mApplication = this;
	}
	/*
	 * 单例模式 : 公共静态获取方法
	 */
	public static MyApplication getInstance() {
		return mApplication;
	}
}

<manifest xmlns:android="http://schemas.android.com/apk/res/android" >

    <application
        android:name=".MyApplication" >
        
    </application>

</manifest>

    Collections.sort(mList, new Comparator<Integer>() {  
    	
        @Override  
        public int compare(Integer a, Integer b) {  
            if (a>b) {  
                return 1;  
            }  
            return -1;  
        }  
    });  

		float pi = 3.1415926f;
		DecimalFormat decimalFormat = new DecimalFormat("#.00");
		String formatData = decimalFormat.format(pi);
		System.out.println(formatData);
		
		System.out.println(new DecimalFormat("#.00").format(pi));

		float pi = 3.1415926f;
		BigDecimal bigDecimal = new BigDecimal(pi);
		float result = bigDecimal.setScale(2, BigDecimal.ROUND_HALF_UP).floatValue();
		System.out.println(result);

        BigDecimal bd1=new BigDecimal(0.05);
        System.out.println(bd1.toString());
        BigDecimal bd2=new BigDecimal("0.05");
        System.out.println(bd2.toString());

        0.05000000000000000277555756156289135105907917022705078125
        0.05

        BigDecimal bd3=new BigDecimal(String.valueOf(0.05));
        BigDecimal bd4=new BigDecimal(String.valueOf(0.01));
        System.out.println((bd3.add(bd4)).doubleValue());

        BigDecimal bd5=new BigDecimal(String.valueOf(0.05));
        BigDecimal bd6=new BigDecimal(String.valueOf(0.01));
        System.out.println((bd5.subtract(bd6)).doubleValue());

        BigDecimal bd7=new BigDecimal(String.valueOf(0.05));
        BigDecimal bd8=new BigDecimal(String.valueOf(0.01));
        System.out.println((bd7.multiply(bd8)).doubleValue());

        //这里没有考虑数据错误的可能情况
        //定义了精确位数
        int scale=10; 
        BigDecimal bd9=new BigDecimal(String.valueOf(0.05));
        BigDecimal bd10=new BigDecimal(String.valueOf(0.03));
        System.out.println((bd9.divide(bd10,scale,BigDecimal.ROUND_HALF_EVEN)).doubleValue()); 

        //四舍五入
        scale=4;
        BigDecimal bd11=new BigDecimal(String.valueOf(3.1415926));
        System.out.println(bd11.setScale(scale,BigDecimal.ROUND_HALF_UP).toString());

<string name="delete_success">删除<xliff:g id="name">%1$s</xliff:g>成功</string> 

<string name="upload_success">%1$s上传到%2$s成功</string>

Resources resources = this.getResources();
int imageIndentify = resources.getIdentifier(imageName, "drawable","chao.yun.demo");

resources.getIdentifier(imageName, "drawable","chao.yun.demo");

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    
    <LinearLayout 
        android:id="@+id/ll_1"
        android:layout_width="fill_parent"
        android:layout_height="0px"
        android:layout_weight="1"></LinearLayout>
    
    <LinearLayout 
        android:id="@+id/ll_2"
        android:layout_width="fill_parent"
        android:layout_height="0px"
        android:layout_weight="1"></LinearLayout>
    
    <LinearLayout 
        android:id="@+id/ll_3"
        android:layout_width="fill_parent"
        android:layout_height="0px"
        android:layout_weight="1"></LinearLayout>

</LinearLayout>

public class MainActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        LinearLayout ll_1 = (LinearLayout) findViewById(R.id.ll_1);
        LinearLayout ll_2 = (LinearLayout) findViewById(R.id.ll_2);
        LinearLayout ll_3 = (LinearLayout) findViewById(R.id.ll_3);
        
        Resources resources = this.getResources();

	String imageName = "image_" + 1;
	int imageIndentify = resources.getIdentifier(imageName, "drawable","chao.yun.demo");
	ll_1.setBackgroundResource(imageIndentify);

	imageName = "image_" + 2;
	imageIndentify = resources.getIdentifier(imageName, "drawable","chao.yun.demo");
	ll_2.setBackgroundResource(imageIndentify);

	imageName = "image_" + 3;
	imageIndentify = resources.getIdentifier(imageName, "drawable","chao.yun.demo");
	ll_3.setBackgroundResource(imageIndentify);
    }
}

myMenuItem.setIcon(android.R.drawable.ic_menu_save);

android:icon="@android:drawable/ic_menu_save"