Android(安卓)自定义view(二) 如何实现自定义组件
本文为翻译官网的介绍,官网地址:http://developer.android.com/guide/topics/ui/custom-components.html
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
1. 最普通的作法是,继承自View,实现你的自定义组件
2. 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
3. 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
4. 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。
5. 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. |
| Called after a view and all of its children has been inflated from XML. | |
Layout |
| Called to determine the size requirements for this view and all of its children. |
| Called when this view should assign a size and position to all of its children. | |
| Called when the size of this view has changed. | |
Drawing |
| Called when the view should render its content. |
Event processing |
| Called when a new key event occurs. |
| Called when a key up event occurs. | |
| Called when a trackball motion event occurs. | |
| Called when a touch screen motion event occurs. | |
Focus |
| Called when the view gains or loses focus. |
| Called when the window containing the view gains or loses focus. | |
Attaching |
| Called when the view is attached to a window. |
| Called when the view is detached from its window. | |
| 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
/* * 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:
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: 1. 通常需要创建一个类,继承自一个Layout,或者ViewGroup。 2. 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 3. 可以创建监听器,监听处理一些可能的动作 4. 可能有一些 属性的 get / set 方法 5. 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 6. 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 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:
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
使用完全限定类名,引入自定义组件。使用$引用内部类。
Android 自定义view(一) 基本实现方式和自定义属性: http://blog.csdn.net/jjwwmlp456/article/details/38728519
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