What is android:layout_alignLeft in Android?

问题

i couldnt understand the attribute android:layout_alignLeft .i am new to android development.

<RelativeLayout 
        android:id="@+id/r5"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/r4"

        > <TextView
              android:id="@+id/tv3"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:layout_centerHorizontal="true"
              android:layout_centerVertical="true"
              android:layout_marginTop="10dp"
               android:textSize="16sp"
              android:textColor="#663300"
              android:text="TextView"

               />

          <TextView
              android:id="@+id/tv5"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"            
              android:layout_marginTop="10dp"

              android:layout_alignLeft="@id/tv3"
               android:textSize="16sp"
              android:textColor="#663300"
              android:text="TextView"


               />
         <TextView
              android:id="@+id/tv6"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:layout_toRightOf="@id/tv5"
              android:layout_marginTop="10dp"
               android:textSize="16sp"
              android:textColor="#663300"
              android:text="TextView"

               />

          </RelativeLayout>

anyone can explain clearly?what is the difference between android:layout_Leftof and android:layout_alignLeft?

回答1:

layout_alignLeft makes the left edge of your view match the left edge of the view whose ID you use as the parameters.

layout_toLeftOf makes your view placed to the left side of the view whose ID you use (the right edge will be aligned with the left edge of the other view).

回答2:

ALIGN_LEFT Rule that aligns a child's left edge with another child's left edge.

LEFT_OF Rule that aligns a child's right edge with another child's left edge.

in your above example the align left is used in a way below.

 tv5 textview is align left of the tv3 layout in android.

回答3:

Both parameters are used in relative layout. Talking about android:layout_Leftof, this parameter makes your view to be placed "to the left" (not align) of view whose id you are passing as a value.On the other hand android:layout_alignLeft will place you view starting from the same point(from left in this case) where the view your have passed the id is starting. Also int this case, your view may overlap the other view (as sometimes it is used to keep a view inside another view)

回答4:

android:layout_alignLeft aligns both left sides. (pic 1)

android:layout_toLeftOf aligns one layout to the left of another. (pic 2)

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#D6D6D6"
    android:orientation="vertical">


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <LinearLayout
            android:layout_width="400dp"
            android:layout_height="400dp"
            android:layout_alignLeft="@+id/ll1"
            android:background="#00FF00"
            android:orientation="vertical">  </LinearLayout>

            <LinearLayout
                android:id="@+id/ll1"
                android:layout_width="200dp"
                android:layout_alignParentRight="true"
                android:layout_height="200dp"
                android:background="#00FFFF"
                android:orientation="vertical"></LinearLayout>


    </RelativeLayout>


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="50dp">


        <LinearLayout
            android:layout_width="400dp"
            android:layout_height="400dp"
            android:layout_toLeftOf="@+id/ll2"
            android:background="#00FF00"
            android:orientation="vertical"></LinearLayout>

            <LinearLayout
                android:id="@+id/ll2"
                android:layout_width="200px"
                android:layout_height="200px"
                android:layout_alignParentRight="true"
                android:background="#00FFFF"
                android:orientation="vertical">
        </LinearLayout>

    </RelativeLayout>

</LinearLayout>

回答5:

android:layout_alignLeft is for eg: you are using a TextView.Let's take an eg. There are two

textview.ur first text id as @+id/t1. Next textview say t2is @+id/t2. if you want to place

second textview to the left of first textview, you can refer the id in the t2 ie

android:layout_Leftof="@+id/t1"

来源：https://stackoverflow.com/questions/14639689/what-is-androidlayout-alignleft-in-android