使用Kotlin开发Android应用7-自定义控件

Define a Custom Widget in Android App

在 Android 应用中定义个自定义控件

1. 使用 XML 自定义视图 / 控件

一个简单的例子，自定义单元条 CellBar

1、xml 布局如下:

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/white"
    android:padding="10dp">
    <ImageView
        android:id="@+id/cell_bar_icon"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>
    <TextView
        android:id="@+id/cell_bar_label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="5dp"
        android:textColor="@color/black"
        android:text="android:"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toEndOf="@id/cell_bar_icon"/>
    <TextView
        android:id="@+id/cell_bar_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="android2:"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@id/cell_bar_go"/>

    <ImageView
        android:id="@+id/cell_bar_go"
        android:src="@drawable/ic_keyboard_arrow_right"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

2、代码如下（继承 ConstraintLayout）:

class CellBar : ConstraintLayout {

    private var iconView: ImageView? = null
    private var labelView: TextView? = null
    private var contentView: TextView? = null

    @DrawableRes
    var icon: Int = 0
        set(value) {
            field = value
            iconView?.setImageResource(value)
        }

    var label: CharSequence? = null
        set(value) {
            field = value
            labelView?.text = value
        }

    var text: CharSequence? = null
        set(value) {
            field = value
            contentView?.text = value
        }

    constructor(context: Context) : this(context, null)
    constructor(context: Context, attrs: AttributeSet?) : this(context, attrs, 0)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr) {init(context)
        attrs?.let {retrieveAttributes(attrs) }
    }

    fun init(context: Context) {val view = LayoutInflater.from(context).inflate(R.layout.widget_cell_bar,this)
        iconView = view.findViewById(R.id.cell_bar_icon)
        labelView = view.findViewById(R.id.cell_bar_label)
        contentView = view.findViewById(R.id.cell_bar_text)
    }

    private fun retrieveAttributes(attrs: AttributeSet) {val typedArray = context.obtainStyledAttributes(attrs, R.styleable.CellBar)
        val iconRes = typedArray.getResourceId(R.styleable.CellBar_icon, 0)
        if (iconRes != 0)
            icon = iconRes
        label = typedArray.getText(R.styleable.CellBar_label)
        text = typedArray.getText(R.styleable.CellBar_text)
        typedArray.recycle()}
}

上述代码 重写了构造器。在构造器中：1 加载 xml 布局文件，2 获取控件，3 获取属性，4 将属性赋值到控件上

3、添加自定义属性 res/values/attrs.xml

<resources>
    <declare-styleable name="CellBar">
        <attr name="icon" format="reference" />
        <attr name="label" format="string" />
        <attr name="text" format="string" />
    </declare-styleable>
</resources>

4、使用自定义控件

  <com.edgar.movie.widget.CellBar
    android:layout_marginTop="20dp"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:icon="@drawable/ic_sofa"
    app:label="看电影"/>

Reference 参考

• 本文示例