LinearLayout子项未显示

Question

I want to create the below layout.

Layout structure :

LinearLayout
  --> ImageButton
  --> TextView
  --> Button

What I want is to display the Textview's text center horizontally inside its parent layout.

But I can't event get there, right now the button is missing :

My code :

     <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="60dp"
            android:orientation="horizontal"
            android:background="@color/toolBar"
            android:gravity="center">

            <ImageButton
                android:layout_width="40dp"
                android:layout_height="40dp"
                android:src="?attr/homeAsUpIndicator"
                android:background="@drawable/back_button"
                android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
                android:onClick="activityFinish"
                android:clickable="true"
                android:focusable="true"
                android:layout_marginTop="5dp"
                android:layout_marginBottom="5dp"
                android:layout_marginLeft="10dp"
                android:layout_marginRight="10dp"
                />

            <TextView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:id="@+id/qaa_book_name"
                android:textColor="@color/white"
                android:textSize="20sp"
                android:textStyle="bold"
                android:gravity="center"
                android:text="xxx"
                />

            <Button
                android:id="@+id/qaa_end_test"
                android:layout_width="wrap_content"
                android:layout_height="match_parent"
                android:visibility="visible"
                android:text="yyy"
                android:textColor="@color/white"/>

        </LinearLayout>

Answer 1

Check this updated layout :

<LinearLayout
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:orientation="horizontal"
        android:background="@color/toolBar"
        android:gravity="center">

        <ImageButton
            android:layout_width="40dp"
            android:layout_height="40dp"
            android:src="?attr/homeAsUpIndicator"
            android:background="@drawable/back_button"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            android:onClick="activityFinish"
            android:clickable="true"
            android:focusable="true"
            android:layout_marginTop="5dp"
            android:layout_marginBottom="5dp"
            android:layout_marginLeft="10dp"
            android:layout_marginRight="10dp"
            />

        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/qaa_book_name"
            android:textColor="@color/white"
            android:textSize="20sp"
            android:textStyle="bold"
            android:gravity="center"
            android:text="xxx"
            android:layout_weight="1"
            />

        <Button
            android:id="@+id/qaa_end_test"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:visibility="visible"
            android:text="yyy"
            android:textColor="@color/white"/>

    </LinearLayout>

---

Edit:

According to LinearLayout documentation,

When you set android:orientation to specify whether child views are displayed in a row or column,

You can set android:layout_weight on individual child views to specify how linear layout divides remaining space amongst the views it contains.

---

android:layout_weight : This attribute assigns an "importance" value to a view in terms of how much space it should occupy on the screen. A larger weight value allows it to expand to fill any remaining space in the parent view. Child views can specify a weight value, and then any remaining space in the view group is assigned to children in the proportion of their declared weight. Default weight is zero .

That means when you put weight 1 (to TextView in your case) , it'll take at least all space unless next to last elements ( Button in our case) acquires space in container, So TextView spreads to fill all space once Button takes up space by it's wrap_content property.

Refer this guide by official doc

Hope now, i make it clear !

Answer 2

LinearLayout supports a special property for its children called layout_weight . Specifying this property on one or more child views will make the LinearLayout first lay everything out as normal, and then give all the extra space left over to its children that have weight specified (and it divides this extra space based on the value for each child with weight).

The most common use case for weight is to give it to only a single child, effectively saying "give everything else as much room as it needs, and then give this one child all the rest of the space". That's exactly what you want here; you have two views on either side that should be wrap_content , and then one view in the middle that you want to have fill the space left over.

When you only have one child with layout_weight , conventionally you give its matching dimension (width for a horizontal layout, height for a vertical layout) a size of 0dp . This is because LinearLayout still has to do that first pass to lay everything out before determining how much "extra" space it has left over, and sizing a 0dp view is faster than sizing a wrap_content view... and it's going to be stretched to the same size no matter what dimension you give.

With all that in mind, your layout should look like this:

<LinearLayout
    android:orientation="horizontal"
    ...>

    <ImageButton
        android:layout_width="40dp"
        android:layout_height="40dp"
        .../>

    <TextView
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        .../>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        .../>

</LinearLayout>

Answer 3

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/bg_image">

    <ImageView
        android:id="@+id/img_back"
        android:layout_width="@dimen/_30sdp"
        android:layout_height="@dimen/_30sdp"
        android:src="@drawable/ic_arrow_back_black_24dp"
        android:onClick="onClick"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="center"
        android:text="xxx"
        android:textColor="@android:color/black"
        android:textSize="@dimen/_24sdp"
        android:textStyle="bold" />

    <Button
        android:id="@+id/btn_yyy"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="yyy"
        android:layout_gravity="end"
        android:textAllCaps="false"
        android:textSize="@dimen/textsize_18sp" />

</FrameLayout>

Answer 4

   <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/qaa_book_name"
        android:textColor="@color/white"
        android:textSize="20sp"
        android:textStyle="bold"
        android:gravity="center"
        android:text="xxx"
        android:layout_weight="1"
        />

   Problem is in your text view {android:layout_width="match_parent"}  replace it 
   like this   android:layout_width="wrap_content"

Answer 5

The default weight of all views in a LinearLayout is 0. The least the weight of a view, the hightest its priority is.

If your put to a view : android:layout_weight="1" while the other views are at default weight, then the views with default weight will get the priority. Their size in the LinearLayout will be attributed before the view with weight 1.

I hope this info helps you understand why a single line fixed your issue.