约束布局 ConstraintLayout 的使用（一）

ConstraintLayout 是一个 ViewGroup，可用作支持库，您可以在从 API 级别 9（Gingerbread）开始的 Android 系统上使用。 RelativeLayout 和 ConstraintLayout 有许多类似的地方。你可以相对地放置你的子视图，这第一眼看起来和 ConstraintLayout 实现的一样。但 RelativeLayout 有一些你可能早就知道的问题。 </span> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <?xml version="1.0" encoding="utf-8"?> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <RelativeLayout <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> xmlns:android="http://schemas.android.com/apk/res/android" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_width="match_parent" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_height="match_parent"> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span><Button <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:id="@+id/button" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_width="wrap_content" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_height="wrap_content" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:text="Button" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_alignParentBottom="true" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_alignParentEnd="true" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_alignParentRight="true" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_marginBottom="34dp" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_marginEnd="24dp" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_marginRight="24dp"/> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span></RelativeLayout> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <span class="token md md-pre" style="box-sizing: border-box; outline: none !important; color: rgba(128, 128, 128, 0.6); font-style: normal; font-weight: normal;"> 上面的代码在容器的右下方放了一个按钮 如果把 RelativeLayout 的 layout_height 改成 wrap_content，按钮就直接在容器的底部。 如果使用 ConstraintLayout 就可以避免这个问题 </span> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <?xml version="1.0" encoding="utf-8"?> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_width="match_parent" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_height="wrap_content" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> xmlns:app="http://schemas.android.com/apk/res-auto"> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span><Button <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:id="@+id/button" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_width="wrap_content" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_height="wrap_content" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:text="Button" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> app:layout_constraintBottom_toBottomOf="parent" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> app:layout_constraintEnd_toEndOf="parent" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_marginBottom="34dp" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_marginEnd="24dp" <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> android:layout_marginRight="24dp"/> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span></android.support.constraint.ConstraintLayout> <span class="token lf" style="box-sizing: border-box; outline: none !important;"></span> <span class="token md md-pre" style="box-sizing: border-box; outline: none !important; color: rgba(128, 128, 128, 0.6); font-style: normal; font-weight: normal;"> 具体使用请看下一篇： 约束布局 ConstraintLayout 的使用（二）