原文地址：http://blog.csdn.net/shineflowers/article/details/41348565
参考链接：http://blog.csdn.net/jjwwmlp456/article/details/41076699
简介
Android提供了用于构建UI的强大的组件模型。两个基类：View和ViewGroup。
可用Widget的部分名单包括Button， TextView， EditText， ListView， CheckBox，RadioButton， Gallery， Spinner，以及一些有特别作用的组件： AutoCompleteTextView， ImageSwitcher和 TextSwitcher。
可用的布局有：LinearLayout，FrameLayout，RelativeLayout，AbsoluteLayout，GridLayout (later on api level 14 or v7-support)
基本做法
1. 继承自View或View的子类
2. 重写父类的一些方法，如：onDraw()，onMeasure()，onLayout()等
3. 使用自定义的组件类。
完全自定义组件
- 最普通的作法是，继承自View，实现你的自定义组件
- 提供一个构造函数，采用有属性参数的，也可以使用自定义属性
- 你可能想在组件中创建自己的事件监听器，属性访问器和修改器，或其他行为
- 几乎肯定要重写onDraw()，onMeasure()。默认onDraw()什么也没作，onMeasure()则设置一个100x100的尺寸。
- 根据需要重写其他方法 ...
onDraw()和onMeasure()
onDraw()，提供一个Canvas，可以绘制2D图形。
若要绘制3D图形，请继承GLSurfaceView，参见，api-demo下的 GLSurfaceViewActivity
onMeasure() 测量组件
1. 宽度和高度在需要测量时调用该方法
2. 应该进行测量计算组件将需要呈现的宽度和高度。它应该尽量保持传入的规格范围内，尽管它可以选择超过它们（在这种情况下，父视图可以选择做什么，包括裁剪，滚动，抛出一个异常，或者要求onMeasure()再次尝试，或使用不同的测量规格）
3. 宽高计算完毕后，必须调用用setMeasuredDimession(int width, int height)，进行设置。否则将抛出一个异常
下面是一些View中可被调用的方法总结(未全部包含，可自行查看类似onXxx的方法)：
Category
Methods
Description
Creation
Constructors
There is a form of the constructor that are called when the view is created from code and a form that is called when the view is inflated from a layout file. The second form should parse and apply any attributes
defined in the layout file.
onFinishInflate()
Called after a view and all of its children has been inflated from XML.
Layout
onMeasure(int,
int)
Called to determine the size requirements for this view and all of its children.
onLayout(boolean,
int, int, int, int)
Called when this view should assign a size and position to all of its children.
onSizeChanged(int,
int, int, int)
Called when the size of this view has changed.
Drawing
onDraw(Canvas)
Called when the view should render its content.
Event processing
onKeyDown(int,
KeyEvent)
Called when a new key event occurs.
onKeyUp(int,
KeyEvent)
Called when a key up event occurs.
onTrackballEvent(MotionEvent)
Called when a trackball motion event occurs.
onTouchEvent(MotionEvent)
Called when a touch screen motion event occurs.
Focus
onFocusChanged(boolean,
int, Rect)
Called when the view gains or loses focus.
onWindowFocusChanged(boolean)
Called when the window containing the view gains or loses focus.
Attaching
onAttachedToWindow()
Called when the view is attached to a window.
onDetachedFromWindow()
Called when the view is detached from its window.
onWindowVisibilityChanged(int)
Called when the visibility of the window containing the view has changed.
自定义View示例
adi-demo下的示例：LabelView
[java] view
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/*
- 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 android.widget;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.view.View;
/**
- 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 {
/**- Constructor. This version is only needed if you will be instantiating
- the object manually (not from a layout XML file).
- @param context the application environment
*/
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();Resources.StyledAttributes a = context.obtainStyledAttributes(attrs,
R.styleable.LabelView);CharSequence s = a.getString(R.styleable.LabelView_text);
if (s != null) {
setText(s.toString());
}ColorStateList textColor = a.getColorList(R.styleable.
LabelView_textColor);
if (textColor != null) {
setTextColor(textColor.getDefaultColor(0));
}int textSize = a.getInt(R.styleable.LabelView_textSize, 0);
if (textSize > 0) {
setTextSize(textSize);
}a.recycle();
}*/
private void initLabelView() {
mTextPaint = new Paint();
mTextPaint.setAntiAlias(true);
mTextPaint.setTextSize(16);
mTextPaint.setColor(0xFF000000);mPaddingLeft = 3;
mPaddingTop = 3;
mPaddingRight = 3;
mPaddingBottom = 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;
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) + mPaddingLeft
+ mPaddingRight;
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;
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()) + mPaddingTop
+ mPaddingBottom;
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, mPaddingLeft, mPaddingTop - mAscent, mTextPaint);
}
private Paint mTextPaint;
private String mText;
private int mAscent;
}
应用该自定义组件的layout xml：
[html] view
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<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="match_parent"
android:layout_height="wrap_content">
<com.example.<strong style="color:black; background-color:#ffff66">android</strong>.apis.view.LabelView
<strong style="color:black; background-color:#ffff66">android</strong>:background="@drawable/red"
<strong style="color:black; background-color:#ffff66">android</strong>:layout_width="match_parent"
<strong style="color:black; background-color:#ffff66">android</strong>:layout_height="wrap_content"
app:text="Red"/>
<com.example.<strong style="color:black; background-color:#ffff66">android</strong>.apis.view.LabelView
<strong style="color:black; background-color:#ffff66">android</strong>:background="@drawable/blue"
<strong style="color:black; background-color:#ffff66">android</strong>:layout_width="match_parent"
<strong style="color:black; background-color:#ffff66">android</strong>:layout_height="wrap_content"
app:text="Blue" app:textSize="20dp"/>
<com.example.<strong style="color:black; background-color:#ffff66">android</strong>.apis.view.LabelView
<strong style="color:black; background-color:#ffff66">android</strong>:background="@drawable/green"
<strong style="color:black; background-color:#ffff66">android</strong>:layout_width="match_parent"
<strong style="color:black; background-color:#ffff66">android</strong>:layout_height="wrap_content"
app:text="Green" app:textColor="#ffffffff" /> </LinearLayout>
该示例演示了：
1. 继承自View的完全自定义组件
2. 带参数的构造函数(一些属性参数在xml中设置)。还使用了自定义属性 R.styleable.LabelView
3. 一些标准的public 方法，如setText()、setTextSize()、setTextColor()
4. onMeasure()测量组件尺寸，内部由measureWidth(int measureSpec) 和 measureHeight(int measureSpec)来测量。
5. onDraw()将Label绘制到画面Canvas上
复合组件
由一些现有组件，复合成一个新的组件。
要创建一个复合组件：
- 通常需要创建一个类，继承自一个Layout，或者ViewGroup。
- 在构造函数中，需要先调用父类相应的构造函数。然后设置一些需要的组件用于复合。可以使用自定义属性
- 可以创建监听器，监听处理一些可能的动作
- 可能有一些 属性的 get / set 方法
- 如果继承自某一Layout类时，不需要重写onDraw()和onMeasure()，因为Layout类中有默认的行为。如有必要，当然也可以重写
- 可能重写其他一些onXxx()，以达到你想要的效果
复合组件示例
api-demo下的List4和List6里的内部类SpeachView，以下为List6中的源码
[java] view
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private class SpeechView extends LinearLayout {
public SpeechView(Context context, String title, String dialogue, boolean expanded) {
super(context);
this.setOrientation(VERTICAL);
// Here we build the child views in code. They could also have
// been specified in an XML file.
mTitle = new TextView(context);
mTitle.setText(title);
addView(mTitle, new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
mDialogue = new TextView(context);
mDialogue.setText(dialogue);
addView(mDialogue, new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
mDialogue.setVisibility(expanded ? VISIBLE : GONE);
}
/**
* Convenience method to set the title of a SpeechView
*/
public void setTitle(String title) {
mTitle.setText(title);
}
/**
* Convenience method to set the dialogue of a SpeechView
*/
public void setDialogue(String words) {
mDialogue.setText(words);
}
/**
* Convenience method to expand or hide the dialogue
*/
public void setExpanded(boolean expanded) {//该方法在List4中没有
mDialogue.setVisibility(expanded ? VISIBLE : GONE);
}
private TextView mTitle;
private TextView mDialogue; }
SpeachView，继承了LinearLayout，纵向布局。内部有一个TextView的title，一个TextView的dialogue。List4完全展开两个TextView；List6点击title可以收缩/展开dialogue。
修改现有View类型
继承自一个现有的View，以增强其功能，满足需要。
sdk中有个记事本NotePad的示例工程。其中有一个类就是扩展了EditText。
在NoteEditor类中：
[java] view
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public static class LinedEditText extends EditText {
private Rect mRect;
private Paint mPaint;
// This constructor is used by LayoutInflater
public LinedEditText(Context context, AttributeSet attrs) {
super(context, attrs);
// Creates a Rect and a Paint object, and sets the style and color of the Paint object.
mRect = new Rect();
mPaint = new Paint();
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setColor(0x800000FF);
}
/**
* This is called to draw the LinedEditText object
* @param canvas The canvas on which the background is drawn.
*/
@Override
protected void onDraw(Canvas canvas) {
// Gets the number of lines of text in the View.
int count = getLineCount(); //edittext中有几行， edittext继承textview
// Gets the global Rect and Paint objects
Rect r = mRect;
Paint paint = mPaint;
/*
* Draws one line in the rectangle for every line of text in the EditText
*/
for (int i = 0; i < count; i++) {
// Gets the baseline coordinates for the current line of text
int baseline = getLineBounds(i, r);//将一行的范围坐标赋给矩形r；返回一行y方向上的基准线坐标
/*
* Draws a line in the background from the left of the rectangle to the right,
* at a vertical position one dip below the baseline, using the "paint" object
* for details.
*/
canvas.drawLine(r.left, baseline + 1, r.right, baseline + 1, paint);//绘制一条线，宽度为原行的宽度，高度为从基线开始+1个像素
}
// Finishes up by calling the parent method
super.onDraw(canvas);
} }
定义
一个public的静态内部类，以便它可以被访问：NoteEditor.MyEditText
它是静态内部类，意味着，它不依靠外部类的成员，不会产生一些“组合的方法”。
继承自EditText
类的初始化
构造函数中，先调用父类的构造方法，并且它是带属性参数的构造函数。在使用时，从一个xml布局文件inflate
重写的方法
只有onDraw()被重写。在onDraw()中绘制了一条蓝色的线，该线从每行文本的的基线开始向下1像素，宽度为行宽。
方法结束前，调用super.onDraw()
使用自定义组件
[html] view
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<view xmlns:android="http://schemas.android.com/apk/res/android"
class="com.example.android.notepad.NoteEditor$LinedEditText"
android:id="@+id/note"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/transparent"
android:padding="5dp"
android:scrollbars="vertical"
android:fadingEdge="vertical"
android:gravity="top"
android:textSize="22sp"
android:capitalize="sentences"
/>
使用完全限定类名，引入自定义组件。使用$引用内部类。