在XML中创建自定义布局以在代码或其他布局xml中初始化

Question

I have encountered an issue i am trying to resolve (or understand better the way it should be done) in creation of custom Layout in Android.

I want to create a custom RelativeLayout class for my use, which is defined in a layout XML file.

my_relative_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<com.mypackage.MyRelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">
    <ImageView
        android:id="@+id/image_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@null"
        android:scaleType="fitStart"
        android:src="@drawable/my_drawable"/>
    <TextView
        android:id="@+id/text_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="@color/title_gray"
        android:layout_below="@id/image_view"
        android:gravity="center"
        android:text="@string/placeholder" />
</com.mypackage.MyRelativeLayout>

Usage

  public class MyRelativeLayout extends RelativeLayout {
        private AttributeSet attrs;
        private ImageView imageView;
        private TextView textView;

        public MyRelativeLayout(Context context) {
            super(context);
        }

        public MyRelativeLayout(Context context, AttributeSet attrs) {
            super(context, attrs);
            this.attrs = attrs;
        }

        public MyRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
            super(context, attrs, defStyleAttr);
            this.attrs = attrs;
        }

        @Override
        protected void onFinishInflate() {
            super.onFinishInflate();
            if (attrs != null) {
                TypedArray a = getContext().getTheme().obtainStyledAttributes(attrs, R.styleable.MyRelativeLayout, 0, 0);
                drawableResource = a.getResourceId(R.styleable.MyRelativeLayout.image_view, 0);
                a.recycle();
            }
            imageView = (ImageView) findViewById(R.id.image_view);
            textView = (TextView) findViewById(R.id.text_view);

            if (drawableResource != 0 && imageView != null) {
                imageView.setImageResource(drawableResource);
            }
        }
    }

My issue is that i want to initialise this layout both in another XML and in code. But as I wrote my class and XML, i can only use it in code by doing:

myLayout = (MyRelativeLayout) LayoutInflater.from(this.getActivity()).inflate(R.layout.my_relative_layout, container, false);

When writing the following in another XML causes the onFinishInflate to fail on getViewById (returns null) and the childrenCount is 0

<com.mypackage.MyRelativeLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_below="@id/another_layout"
    app:image_view="@drawable/my_image" />

and doing the following, won't let me configure the custom image_view attribute.

<include layout="@layout/my_relative_layout"/>

To fix that, i can change the custom layout XML root element to be of type RelativeLayout and add the following to the beginning of onFinishInflate method:

LayoutInflater.from(getContext()).inflate(R.layout.my_relative_layout, this, true);

But the XML won't reference my class.
My questions are,
1. Am i missing something in the definition of the custom layout?
2. What is the correct definition for custom layout?

Thank you in advance!

Answer 1

First you should use the styled attributes in the contractor as shown in this example.

How can you expect from MyRelativeLayout that defined as fallow:

<com.mypackage.MyRelativeLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_below="@id/another_layout"
    app:image_view="@drawable/my_image" />

To be aware of views that are defined in my_relative_layout.xml ?

To make it work you should create a costume layout and add it to com.mypackage.MyRelativeLayout manually.

Some thing like that:

costume_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">
    <ImageView
        android:id="@+id/image_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@null"
        android:scaleType="fitStart"
        android:src="@drawable/my_drawable"/>
    <TextView
        android:id="@+id/text_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="@color/title_gray"
        android:layout_below="@id/image_view"
        android:gravity="center"
        android:text="@string/placeholder" />
</RelativeLayout>

Your costume view

public class MyRelativeLayout extends RelativeLayout {
        private AttributeSet attrs;
        private ImageView imageView;
        private TextView textView;

        public MyRelativeLayout(Context context) {
            super(context);
            init();
        }

        public MyRelativeLayout(Context context, AttributeSet attrs) {
            super(context, attrs);
            init();
        }

        public MyRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
            super(context, attrs, defStyleAttr);
            init();
        }

        private void init(Context context){
            LayoutInflater.from(context).inflate(R.layout.costume_layout, this);
        }
}