Android 小知识

###一、创建Dialog时 Dialog dialog = new Dialog(getApplicationContext()); 传入getApplicationContext()上下文在运行期间为什么报错？

Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application

在这里我们需要先明白3个Context概念：
1、Activity.getApplicationContext()：

Return the context of the single, global Application object of the current process.  This generally should only be used if you need a Context whose lifecycle is separate from the current context, that is tied to the lifetime of the process rather than the current component.

2、Activity.this/View.getContext()：

Returns the context the view is running in, through which it can access the current theme, resources, etc.

3、Activity.getBaseContext():

return the base context as set by the constructor or setBaseContext

Activity.this与getApplicationContext()的生命周期不同， 前者的生命周期依赖于所在的Activity，后者的生命周期依赖于整个应用。所以new Dialog(getApplicationContext())时会发生错误，Dialog依赖的是一个View, 而View对应一个Activity，若传入getApplicationContext()，其生命周期是整个应用，当退出当前Activity的时候，就会报Unable to add window – token null is not for an application的错误，应该传入当前Activity的Context。

###二、二分排序
最近面试时碰到了一个二分排序，由于完全不知道二分排序的思想就GG了；面试结束后就赶紧学习了下二分排序。

####1、算法思想：二分法插入排序是在插入第i个元素时，对前面的0～i-1元素进行折半，先跟他们中间的那个元素比，如果小，则对前半再进行折半，否则对后半进行折半，直到left>right，然后再把第i个元素前1位与目标位置之间的所有元素后移，再把第i个元素放在目标位置上。

####2、分析：
二分排序的时间复杂度是O(n*log2n)，空间复杂度O(1)，是稳定排序。

####3、实现

####以数组的方式实现：

int[] data = { 34, 32, 12, 61, 23, 36, 40, -15, 21, 11 };
		int i, j;
		int low, high, mid;
		int temp;
		for (i = 1; i < data.length; i++) {
			temp = data[i];
			low = 0;
			high = i - 1;
			while (low <= high) {
				mid = (low + high) / 2;
				if (data[mid] > temp)
					high = mid - 1;
				else
					low = mid + 1;

			}
			for (j = i - 1; j > high; j--)
				data[j + 1] = data[j];
			data[high + 1] = temp;
		}
		for (i = 0; i < 10; i++) {
			System.out.printf("%d\t", data[i]);
		}

####以集合的方式实现：

public class BinarySortDemo {

	public static void main(String[] args) {
		List<Integer> datas = new ArrayList<Integer>();
		for(int i=0; i<10; i++){
			datas.add(new Random().nextInt(100));
		}
		for(Integer data : datas){
			System.out.print(" "+data);
		}
		System.out.println();
		sort(datas);
	}

	public static void sort(List<Integer> datas){
		int i;
		int low, high, mid;
		Integer temp;
		for (i = 1; i < datas.size(); i++) {
			temp = datas.get(i);
			low = 0;
			high = i - 1;
			while (low <= high) {
				mid = (low + high) / 2;
				if (datas.get(mid) > temp)
					high = mid - 1;
				else
					low = mid + 1;

			}
			datas.remove(temp);
			datas.add(high + 1, temp);
		}
		for(Integer data : datas){
			System.out.print(" "+data);
		}
	}
}