1.代码设置

View v = findViewById(R.id.content);
v.getBackground().setAlpha(100);
说明： 0~255透明度值，0表示完全透明，255表示完全不透明。
具体见下面的透明度数值表

2.xml设置

如下图，1A即透明度10，加在了color前面。

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"><corners android:radius="10dp" /><strokeandroid:width="1dp"android:color="@android:color/black" /><solid android:color="@android:color/white"/>//如下图，1A即透明度10，加在了color前面。<solid android:color="#1A7190FF"/></shape>

3.透明度数值表

0% 00
1% 03
2% 05
3% 08
4% 0A
5% 0D
6% 0F
7% 12
8% 14
9% 17
10% 1A
11% 1C
12% 1F
13% 21
14% 24
15% 26
16% 29
17% 2B
18% 2E
19% 30
20% 33
21% 36
22% 38
23% 3B
24% 3D
25% 40
26% 42
27% 45
28% 47
29% 4A
30% 4D
31% 4F
32% 52
33% 54
34% 57
35% 59
36% 5C
37% 5E
38% 61
39% 63
40% 66
41% 69
42% 6B
43% 6E
44% 70
45% 73
46% 75
47% 78
48% 7A
49% 7D
50% 80
51% 82
52% 85
53% 87
54% 8A
55% 8C
56% 8F
57% 91
58% 94
59% 96
60% 99
61% 9C
62% 9E
63% A1
64% A3
65% A6
66% A8
67% AB
68% AD
69% B0
70% B3
71% B5
72% B8
73% BA
74% BD
75% BF
76% C2
77% C4
78% C7
79% C9
80% CC
81% CF
82% D1
83% D4
84% D6
85% D9
86% DB
87% DE
88% E0
89% E3
90% E6
91% E8
92% EB
93% ED
94% F0
95% F2
96% F5
97% F7
98% FA
99% FC
100% FF