Bearded-android-docs

Created Sunday 10 November 2013

• http://developer.android.com/training/custom-views/%E2%80%8E
• http://www.vogella.com/articles/AndroidCustomViews/article.html

• To allow the Android Developer Tools to interact with your view, at a minimum you must provide a constructor that takes a Context and an AttributeSet object as parameters.

To control the view with XML:

• define custom attributes for your view in a <declare-styleable> resource element
• Specify values for the attributes in your XML layout
• Retrieve attribute values at runtime
• Apply the retrieved attribute values to your view

Defining Custom XML Attributes

@Example (res/values/attrs.xml file)
<resources>
   <declare-styleable name="PieChart">
       <attr name="showText" format="boolean" />
       <attr name="labelPosition" format="enum">
           <enum name="left" value="0"/>
           <enum name="right" value="1"/>
       </attr>
   </declare-styleable>
</resources>

Using Custom XML Attributes

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:custom="http://schemas.android.com/apk/res/[yourpackagename]">
 <com.example.customviews.charting.PieChart
     custom:showText="true"
     custom:labelPosition="left" />
</LinearLayout>

Note: You can use any namespace instead of custom.

Setting Custom XML Attributes in the View

public PieChart(Context context, AttributeSet attrs) {
   super(context, attrs);
   

TypedArray a = context.getTheme().obtainStyledAttributes(
attrs,
R.styleable.PieChart,
0, 0);

try {
mShowText = a.getBoolean(R.styleable.PieChart_showText, false);
mTextPos = a.getInteger(R.styleable.PieChart_labelPosition, 0);
} finally {
a.recycle();
}
}

Note: use #obtainStyledAttributes to get a TypedArray. Make sure to call #recycle when you're done.

Layout

• All views must know how to measure and layout themselves.
• #requestLayout tells the view to measure and layout itself. This method calls #requestLayout on its parent so its potentially expensive. You don't normally override this.
• #onMeasure determines the size for the view and its children. It must set the dimension via a call to #setMeasuredDimension.
• #onLayout (in the parent) positions child views based on the result of #onMeasure. This call happens typically once.