Android UI杂谈---layout_weight

对Android 中 LinearLayout中属性layout_weight讨论：

（一）

（1）当android:orientation=”horizontal”android:layout_width=”0dp”时：

<?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="horizontal" >

<TextView
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:background="#C82D25"
android:text="test activity1" />

<TextView
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="2"
android:background="#EBF0F3"
android:text="test activity2" />

<TextView
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="3"
android:background="#F2CACA"
android:text="test activity3" />

</LinearLayout>

表现：



（2）当

android:orientation=”horizontal”android:layout_width=”match_parent”时：

<?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="horizontal" >

<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:background="#C82D25"
android:text="test activity1" />

<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="2"
android:background="#EBF0F3"
android:text="test activity2" />

<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="3"
android:background="#F2CACA"
android:text="test activity3" />

</LinearLayout>

表现：


（3）当

android:orientation=”horizontal”且 android:layout_width=”wrap_content”时：

<?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="horizontal" >

<TextView
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_weight="1"
android:background="#C82D25"
android:text="test activity1" />

<TextView
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_weight="2"
android:background="#EBF0F3"
android:text="test activity2" />

<TextView
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_weight="3"
android:background="#F2CACA"
android:text="test activity3" />

</LinearLayout>

表现：



总结：

表现最佳的是第一种，第二种把第三个TextView挤掉了，第三种没有按比例排列，完全失去了layout_weight属性的作用。

从源码角度分析：

google LinearLayout源码：

if (widthMode == MeasureSpec.EXACTLY && lp.width == 0 && lp.weight > 0) {
// Optimization: don't bother measuring children who are going to use
// leftover space. These views will get measured again down below if
// there is any leftover space.
if (isExactly) {
mTotalLength += lp.leftMargin + lp.rightMargin;
} else {
final int totalLength = mTotalLength;
mTotalLength = Math.max(totalLength, totalLength +
lp.leftMargin + lp.rightMargin);
}

// Baseline alignment requires to measure widgets to obtain the
// baseline offset (in particular for TextViews). The following
// defeats the optimization mentioned above. Allow the child to
// use as much space as it wants because we can shrink things
// later (and re-measure).
if (baselineAligned) {
final int freeWidthSpec = MeasureSpec.makeSafeMeasureSpec(
MeasureSpec.getSize(widthMeasureSpec), MeasureSpec.UNSPECIFIED);
final int freeHeightSpec = MeasureSpec.makeSafeMeasureSpec(
MeasureSpec.getSize(heightMeasureSpec), MeasureSpec.UNSPECIFIED);
child.measure(freeWidthSpec, freeHeightSpec);
} else {
skippedMeasure = true;
}
}

例子：

如果有这样的需求：



右边的箭头不想因为左边的字内容太多被挤掉可以这样写：

<LinearLayout
android:id="@+id/select_deal_card_list_click"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="13dp"
android:background="@drawable/selector_card_list_bg_end"
android:clickable="true"
android:orientation="horizontal"
android:gravity="center"
android:padding="7dp" >

<TextView
android:id="@+id/select_deal_card_list_content"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="2111111112222222/卡"
android:singleLine="true"
android:ellipsize="end"
android:layout_weight="1"
android:textColor="@color/common_gray_txt_bg" />

<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/select_ico" />
</LinearLayout>