Android布局出现错误“嵌套的权重不利于性能”

Question

im trying to do this layout above

and here is my code

 <?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="vertical" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="0.80"
        android:orientation="horizontal" >

        <ImageView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="0.50"
            android:padding="10dp" />

        <RelativeLayout>
        </RelativeLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="0.50"
            android:orientation="vertical" >
        </LinearLayout>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="0.20"
        android:orientation="vertical" >
    </LinearLayout>

</LinearLayout>

In ImageView, i got the error "Nested weights are bad for perfomance". I would to understand why this happening and if someone have a better solution for this layout.

Answer 1

The layout_weight attribute is another way of specifying a width or a height in percentage dimensions, and to optimize the calculation of the dimensions you should use 0dp to one of them (the one you are replacing with).

Another optimize tip is to remove the <RelativeLayout></RelativeLayout> that is not being used in your layout.

Please try the solution below:

<?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="vertical" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="0.80"
        android:orientation="horizontal" >

        <ImageView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="0.50"
            android:padding="10dp" />

        <LinearLayout
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="0.50"
            android:orientation="vertical" >
        </LinearLayout>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="0.20"
        android:orientation="vertical" >
    </LinearLayout>

</LinearLayout>

Answer 2

The error "Nested weights are bad for performance" happens because you have a weighted LInearLayout "nested" inside another weighted LinearLayout (see below). In order for Android to perform this it will have to draw the entire screen to get all of the non-nested layout measurements, then draw it all again to calculate the "nested" weighted layouts.

This can be a huge performance hit. However, I built one screen that had 4 layers of nesting and about 100 layouts, including lots of images. Rendering took about 5 milliseconds on newer devices, usually less. So this is really only an issue if you are frequently redrawing the nested layouts (like trying to animation with nested layouts). If you don't see a performance hit that you can measure in your logcat or observe while using your app, don't worry about it. Test thoroughly!

In other words, it's a warning, not an error.

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="0.80"
    android:orientation="horizontal" >

    <ImageView
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="0.50"
        android:padding="10dp" />

    <!-- THIS IS YOUR NESTED WEIGHTED LAYOUT -->
    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="0.50"
        android:orientation="vertical" >
    </LinearLayout>
</LinearLayout>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="0.20"
    android:orientation="vertical" >
</LinearLayout>

Answer 3

I would rather write it as below. Notice using integers instead of fractions:

    <?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="vertical" >

    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="4"
            android:orientation="horizontal" >

        <ImageView
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:padding="10dp" />

        <LinearLayout
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:orientation="vertical" >
        </LinearLayout>
    </LinearLayout>

    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:orientation="vertical" >
    </LinearLayout>

</LinearLayout>