Access attrs in AttributeSet for custom components

Question

I have a custom component containing two text elements that have a customizable method for adjusting the size (two text representations are proportional to 1: 2). Since this is a subclass of RelativeLayout, it does not have the textSize attribute, but I wonder if it is still possible to set the android:textSize in the XML instance for this component, and then grab the textSize attribute from AttributeSet for use with my custom setSize() method in the constructor.

I saw a technique for this with custom attributes, but what if I want to grab an attribute already in the Android lexicon?

Answer 1

Yes it is possible;

Suppose your RelativeLayout declaration (in xml) has textSize defined with 14sp:

 android:textSize="14sp" 

In the constructor of your custom view (the one that takes in the AttributeSet), you can get attributes from the Android namespace as such:

 String xmlProvidedSize = attrs.getAttributeValue("http://schemas.android.com/apk/res/android", "textSize"); 

The value of xmlProvidedSize will be something like this "14.0sp" and perhaps with a little editing of String you can just extract the numbers.

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Another option for declaring your own attribute set will be small, but it is also possible.

So, you have your own custom view, and your TextViews declared something like this:

 public class MyCustomView extends RelativeLayout{ private TextView myTextView1; private TextView myTextView2; // rest of your class here 

big...

Now you also need to make sure that your custom view overrides the constructor, which takes an attribute set as follows:

 public MyCustomView(Context context, AttributeSet attrs){ super(context, attrs); init(attrs, context); //nice, clean method to instantiate your TextViews// } 

ok, let's see what the init () method is now:

 private void init(AttributeSet attrs, Context context){ // do your other View related stuff here // TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.MyCustomView); int xmlProvidedText1Size = a.int(R.styleable.MyCustomView_text1Size); int xmlProvidedText2Size = a.int(R.styleable.MyCustomView_text2Size); myTextView1.setTextSize(xmlProvidedText1Size); myTextView2.setTextSize(xmlProvidedText2Size); // and other stuff here // } 

You are probably wondering where R.styleable.MyCustomView, R.styleable.MyCustomView_text1Size and R.styleable.MyCustomView_text2Size come from; let me dwell on them in detail.

You must declare the attribute names in the attrs.xml file (in the values ​​directory) so that wherever you can use your custom view, the values ​​obtained from these attributes will be passed to your constructor.

So, let's see how you declare these user attributes as you requested: Here is my whole attrs.xml

 <?xml version="1.0" encoding="utf-8"?> <resources> <declare-styleable name="MyCustomView"> <attr name="text1Size" format="integer"/> <attr name="text2Size" format="integer"/> </declare-styleable> </resources> 

Now you can set the size of your TextViews in your XML, but NOT without declaring a namespace in your layout, here's how:

 <com.my.app.package.MyCustomView xmlns:josh="http://schemas.android.com/apk/res-auto" android:id="@+id/my_custom_view_id" android:layout_width="fill_parent" android:layout_height="wrap_content" josh:text1Size="15" josh:text2Size="30" /> 

Notice how I declared the “josh” namespace as the first line in your CustomView attribute set.

Hope this helps Josh

Answer 2

The accepted answer is a bit long. Here is a concise version that I hope will be easy to follow. To add the textSize attribute (or anything that uses dp / sp ) to your custom view, follow these steps:

1. Create your own attribute

Create (or add the following section) in attrs.xml. Pay attention to the dimension format.

 <resources> <declare-styleable name="CustomView"> <attr name="textSize" format="dimension" /> </declare-styleable> </resources> 

2. Set the attribute in the xml layout.

Pay attention to the user namespace app .

 <RelativeLayout 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"> <com.example.myproject.CustomView android:layout_width="wrap_content" android:layout_height="wrap_content" app:textSize="20sp" /> </RelativeLayout> 

3. Get the attribute value in your custom view

Note the use of getDimensionPixelSize . In your custom view, just work with pixels. See this answer if you need to convert to another dimension.

 public class CustomView extends View { private float mTextSize; // pixels public CustomView(Context context, AttributeSet attrs) { super(context, attrs); TypedArray a = context.getTheme().obtainStyledAttributes( attrs, R.styleable.CustomView, 0, 0); try { mTextSize = a.getDimensionPixelSize(R.styleable.CustomView_textSize, 0); } finally { a.recycle(); } } /** * @param size in SP units */ public void setTextSize(int size) { mTextSize = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, size, getResources().getDisplayMetrics()); mTextPaint.setTextSize(mTextSize); invalidate(); requestLayout(); } // ... } 

Notes

• User view documentation