How to work with properties in the interface?

Properties in Android UI resources can be defined in XML files and manipulated programmatically.

For example, in the layout XML (res/layout/activity_main.xml), the android:text property for a TextView:

<TextView  
    android:id="@+id/my_textview"  
    android:layout_width="wrap_content"  
    android:layout_height="wrap_content"  
    android:text="Sample text" />  

To change this property programmatically in an Activity or Fragment:

// Get a reference to the View
TextView myTextView = findViewById(R.id.my_textview);  

// Set new text
myTextView.setText("New text");  

// Change other properties, for example, text color
myTextView.setTextColor(getResources().getColor(R.color.design_default_color_primary));  

Properties can vary: sizes (android:layout_width, android:layout_height), margins (android:padding, android:layout_margin), colors (android:textColor, android:background), behavior (android:clickable, android:visibility), and others, depending on the specific View type.

Some complex properties can be defined in separate XML files, such as styles (res/values/styles.xml) or themes. Applying a style to a View:

<TextView  
    android:id="@+id/my_textview"  
    android:layout_width="wrap_content"  
    android:layout_height="wrap_content"  
    android:text="Sample text with style"  
    style="@style/MyTextViewStyle" />  

Using Data Binding or View Binding simplifies working with properties, providing type-safe access to Views and their properties without findViewById.

Custom View properties are defined using attributes in the res/values/attrs.xml file and then processed in the custom View code.

<declare-styleable name="MyCustomView">  
    <attr name="customText" format="string"/>  
    <attr name="customColor" format="color"/>  
</declare-styleable>  

Reading custom attributes in custom View code:

// Example inside the constructor of a custom View
TypedArray a = context.getTheme().obtainStyledAttributes(
        attrs,
        R.styleable.MyCustomView,
        0, 0);  

try {  
    String text = a.getString(R.styleable.MyCustomView_customText);  
    int color = a.getColor(R.styleable.MyCustomView_customColor, Color.BLACK);  
    // Use the obtained values
} finally {  
    a.recycle(); // Always recycle TypedArray
}