Android开发Tips | Damon Lee 's blog

Android开发Tips

Damon Lee 12月 02, 2018

我们在开发Android应用的时候经常会遇到一些小问题，为了不让这些小问题浪费你的时间，最好还是记录下，毕竟Time is money.

下面是我遇到的一些简单的问题，我会持续更新，算是一些Tips：

给view的background设置selector不生效，因为selector的匹配规则是从上而下，所以我们应把state_pressed和state_selected等属性为ture的情况放在最前面，如果没有给view设置OnClickListener的话一定要给view设置clickable属性为true

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/ic_all_selected" android:state_selected="true"/>
    <item android:drawable="@drawable/ic_all_selected" android:state_pressed="true"/>
    <item android:drawable="@drawable/ic_all_unselected"/>
</selector>

给TextView或者EditText设置setCompoundDrawables时，记得给Drawable对象setBounds

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final Drawable drawable = getResources().getDrawable(R.drawable.ic_add);
drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
textview.setCompoundDrawables(drawable, drawable, drawable, drawable);

当View的maxWidth和maxHeight属性不生效时，不妨试试设置adjustViewBounds的属性为true

<ImageView
        android:id="@+id/img"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:maxWidth="100dp"
        android:maxHeight="100dp"
        android:adjustViewBounds="true"/>

当我们用Fragment嵌套Fragment时，同时Fragment又搭配ViewPager显示内容，会出现内层的Fragment的ViewPager不显示UI或者只显示第一页的问题，其实是因为Activity嵌套Fragment使用ViewPager时应该用getSupportFragmentManager()作为PagerAdapter实例化的参数，而当Fragment嵌套Fragment使用ViewPager时应该用getChildFragmentManager()
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MyPagerAdapter adapter = new MyPagerAdapter(getActivity().getSupportFragmentManager());//❌错误
MyPagerAdapter adapter = new MyPagerAdapter(getChildFragmentManager());//✔️正确

当设计同学给的透明度标注是百分比而不是16进制的时候，总要自己去手动算，所以我找了下表一一对应

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