View编程(5): 自定义View_01_ApiDemo源码研究
2011-12-14 16:06 tang768168 阅读(279) 评论(0) 编辑 收藏 举报android提供的APIDemo中,在/res/values下面有个attrs.xml文件。
其内容如下:
- <?xml version="1.0" encoding="utf-8"?>
- <!-- 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.
- -->
- <resources>
- <!-- These are the attributes that we want to retrieve from the theme
- in app/PreferencesFromCode.java -->
- <declare-styleable name="TogglePrefAttrs">
- <attr name="android:preferenceLayoutChild" />
- </declare-styleable>
- <!-- These are the attributes that we want to retrieve from the theme
- in view/Gallery1.java -->
- <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>
当时,很迷茫。不知道这是什么东西???!!!但是今天需要使用这方面的知识,所以研究一下。
在APIDemo中,com.example.android.apis.view包中CustomView1.java文件中:
- setContentView(R.layout.custom_view_1);
那么,我们研究一下Google提供的该例程吧!
1. CustomView.java
- 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 com.example.android.apis.R;
- import android.app.Activity;
- import android.os.Bundle;
- /**
- * Demonstrates creating a Screen that uses custom views. This example uses
- * {@link com.example.android.apis.view.LabelView}, which is defined in
- * SDK/src/com/example/android/apis/view/LabelView.java.
- *
- */
- public class CustomView1 extends Activity {
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.custom_view_1);
- }
- }
该代码很简单,就是加载一个xml文件,作为显示视图。
2. custom_view_1.xml
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
- xmlns:app="http://schemas.android.com/apk/res/com.example.android.apis"
- android:orientation="vertical"
- android:layout_width="fill_parent"
- android:layout_height="wrap_content">
- <com.example.android.apis.view.LabelView
- android:background="@drawable/red"
- android:layout_width="fill_parent"
- android:layout_height="wrap_content"
- app:text="Red"/>
- <com.example.android.apis.view.LabelView
- android:background="@drawable/blue"
- android:layout_width="fill_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="fill_parent"
- android:layout_height="wrap_content"
- app:text="Green" app:textColor="#ffffffff" />
- </LinearLayout>
可以看出,该xml文件使用了自定义的控件LabelView ,但是你可以看见有一个很陌生的标签app。这是什么东西?
原来,这是自定义的属性文件。所以我们可以自定义属性。但是该属性文件必须是attrs.xml必须放在res/vaules下面。
注意:
- xmlns:app="http://schemas.android.com/apk/res/com.example.android.apis"
app来自这里。
3. attrs.xml
- <resources>
- <!-- These are the attributes that we want to retrieve from the theme
- in app/PreferencesFromCode.java -->
- <declare-styleable name="TogglePrefAttrs">
- <attr name="android:preferenceLayoutChild" />
- </declare-styleable>
- <!-- These are the attributes that we want to retrieve from the theme
- in view/Gallery1.java -->
- <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>
4. LabelView.java
- 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();
- 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);
- }
- }
运行效果:
回调方法调用:
- D/mark ( 2924): LabelView(Context context, AttributeSet attrs) is invoked!
- D/mark ( 2924): LabelView(Context context, AttributeSet attrs) is invoked!
- D/mark ( 2924): LabelView(Context context, AttributeSet attrs) is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onDraw() is invoked!
- D/mark ( 2924): onDraw() is invoked!
- D/mark ( 2924): onDraw() is invoked!
这里注意:
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
- D/mark ( 2924): onMeasure() is invoked!
也就是说,onMeasure()方法被回调六次。那么为什么呢?请关注View编程(6): 自定义View_02_ApiDemo源码研究博文。