Android, Handling Custom view attributes

Google에서 제공하는 커스텀뷰 예제 (LabelView.java)
이 예제를 통해서 커스텀뷰가 갖는 속성값을 레이아웃xml 파일에서 설정하는 방법을 확인한다.

1. 선언 : res/values/attr.xml 에서 커스텀속성 선언
2. 속성값설정: res/layout/main.xml (레이아웃파일)에서 속성설정(사용)
3. 속성값추출: 커스텀뷰 클래스의 생성자에서 커스텀 속성을 추출하여 클래스를 설정

LabelView.java

/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.example.android.apis.view;

// Need the following import to get access to the app resources, since this
// class is in a sub-package.
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

import com.example.android.apis.R;

/**
* Example of how to write a custom subclass of View. LabelView
* is used to draw simple text views. Note that it does not handle
* styled text or right-to-left writing systems.
*
*/
public class LabelView extends View {
private Paint mTextPaint;
private String mText;
private int mAscent;

/**
* Constructor. This version is only needed if you will be instantiating
* the object manually (not from a layout XML file).
* @param context
*/
public LabelView(Context context) {
super(context);
initLabelView();
}

/**
* Construct object, initializing with any attributes we understand from a
* layout file. These attributes are defined in
* SDK/assets/res/any/classes.xml.
*
* @see android.view.View#View(android.content.Context, android.util.AttributeSet)
*/
public LabelView(Context context, AttributeSet attrs) {
super(context, attrs);
initLabelView();

/* 레이아웃 파일에 설정된 커스텀뷰의 속성은 다음과 같은 방법으로 추출하여 사용할 수 있다 */
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.LabelView);

CharSequence s = a.getString(R.styleable.LabelView_text);
if (s != null) {
setText(s.toString());
}

// Retrieve the color(s) to be used for this view and apply them.
// Note, if you only care about supporting a single color, that you
// can instead call a.getColor() and pass that to setTextColor().
setTextColor(a.getColor(R.styleable.LabelView_textColor, 0xFF000000));

int textSize = a.getDimensionPixelOffset(R.styleable.LabelView_textSize, 0);
if (textSize > 0) {
setTextSize(textSize);
}

a.recycle();
}

private final void initLabelView() {
mTextPaint = new Paint();
mTextPaint.setAntiAlias(true);
mTextPaint.setTextSize(16);
mTextPaint.setColor(0xFF000000);
setPadding(3, 3, 3, 3);
}

/**
* Sets the text to display in this label
* @param text The text to display. This will be drawn as one line.
*/
public void setText(String text) {
mText = text;
requestLayout();
invalidate();
}

/**
* Sets the text size for this label
* @param size Font size
*/
public void setTextSize(int size) {
mTextPaint.setTextSize(size);
requestLayout();
invalidate();
}

/**
* Sets the text color for this label.
* @param color ARGB value for the text
*/
public void setTextColor(int color) {
mTextPaint.setColor(color);
invalidate();
}

/**
* @see android.view.View#measure(int, int)
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(measureWidth(widthMeasureSpec),
measureHeight(heightMeasureSpec));
}

/**
* Determines the width of this view
* @param measureSpec A measureSpec packed into an int
* @return The width of the view, honoring constraints from measureSpec
*/
private int measureWidth(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);

if (specMode == MeasureSpec.EXACTLY) {
// We were told how big to be
result = specSize;
} else {
// Measure the text
result = (int) mTextPaint.measureText(mText) + getPaddingLeft()
+ getPaddingRight();
if (specMode == MeasureSpec.AT_MOST) {
// Respect AT_MOST value if that was what is called for by measureSpec
result = Math.min(result, specSize);
}
}

return result;
}

/**
* Determines the height of this view
* @param measureSpec A measureSpec packed into an int
* @return The height of the view, honoring constraints from measureSpec
*/
private int measureHeight(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);

mAscent = (int) mTextPaint.ascent();
if (specMode == MeasureSpec.EXACTLY) {
// We were told how big to be
result = specSize;
} else {
// Measure the text (beware: ascent is a negative number)
result = (int) (-mAscent + mTextPaint.descent()) + getPaddingTop()
+ getPaddingBottom();
if (specMode == MeasureSpec.AT_MOST) {
// Respect AT_MOST value if that was what is called for by measureSpec
result = Math.min(result, specSize);
}
}
return result;
}

/**
* Render the text
*
* @see android.view.View#onDraw(android.graphics.Canvas)
*/
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawText(mText, getPaddingLeft(), getPaddingTop() - mAscent, mTextPaint);
}
}

다음과 같은 방법으로 xml 레이아웃파일에 설정된 속성의 값을 추출하는 것을 확인할 수 있다.

TypedArray a=context.obtainStyledAttributes(attrs, R.styleable.LabelView);
CharSequences=a.getString(R.styleable.LabelView_text);

커스텀뷰 클래스에서 레이아웃파일의 속성을 사용하기 위해서는 일단 사용할 속성을 선언해주어야 한다.
상위 클래스에 이미 선언되어 있는 속성은 다시 이곳에 선언하지 않아도 사용할 수 있으며,
비표준 속성을 선언할 때는 format속성을 함께 사용하여 속성의 형식을 표현해야 한다.

res/values/attrs.xml

<?xml version="1.0" encoding="utf-8"?>


<resources>

<declare-styleable name="TogglePrefAttrs">
<attr name="android:preferenceLayoutChild" />
</declare-styleable>


<declare-styleable name="Gallery1">
<attr name="android:galleryItemBackground" />
</declare-styleable>

<declare-styleable name="LabelView">
<attr name="text" format="string" />
<attr name="textColor" format="color" />
<attr name="textSize" format="dimension" />
</declare-styleable>
</resources>

커스텀 속성은 위처럼 선언하고 format속성을 사용하여 자료의 형식을 지정해주고 있다.

위와같이 선언된 속성은 주 레이아웃파일에서 다음과 같이 커스텀 뷰의 속성으로 설정할 수 있다.

res/layout/custom_view_1.xml

<?xml version="1.0" encoding="utf-8"?>




<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res/com.example.android.apis.view"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content">

<com.example.android.apis.view.LabelView
android:background="@drawable/red"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:text="Red"/>

<com.example.android.apis.view.LabelView
android:background="@drawable/blue"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:text="Blue" app:textSize="20dp"/>

<com.example.android.apis.view.LabelView
android:background="@drawable/green"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:text="Green" app:textColor="#ffffffff" />

</LinearLayout>

Programming

Android, Handling Custom view attributes

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