android系統本身提供了相當豐富的組件如:
Button
,TextView
,EditText
,ListView
,CheckBox
,RadioButton
,Gallery
,Spinner 等
如果系統中提供的組件不能滿足你的需求,你可以自己定義一個組件,如果你只是想對現有的widget做一些小的調整,你之需要繼承這些子類然後重載其中的一些方法即可。
你也可以完全定義自己的組件,基本步驟如下:
1、你定義的組件類(CustomClass)繼承系統的View類
2、你需提供相應的構造函數,來解析XML中的屬性和參數
3、你可以定義自己的監聽事件
4、重載OnDraw()和OnMeasure()方法
5、可以根據需要重載基類中的其他的以on...開頭的方法
Custom View Example:
在android的源碼中有一個很好的例子,我們可以參考一下,就是模擬時鐘的源碼:
/* * Copyright (C) 2006 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.content.Intent; import android.content.IntentFilter; import android.content.BroadcastReceiver; import android.content.res.Resources; import android.content.res.TypedArray; import android.graphics.Canvas; import android.graphics.drawable.Drawable; import android.os.Handler; import android.text.format.Time; import android.util.AttributeSet; import android.view.View; import android.widget.RemoteViews.RemoteView; import java.util.TimeZone; /** * This widget display an analogic clock with two hands for hours and * minutes. */ @RemoteView public class AnalogClock extends View { //繼承自View private Time mCalendar; private Drawable mHourHand; private Drawable mMinuteHand; private Drawable mDial; private int mDialWidth; private int mDialHeight; private boolean mAttached; private final Handler mHandler = new Handler(); private float mMinutes; private float mHour; private boolean mChanged; //提供相應的構造函數 public AnalogClock(Context context) { this(context, null); } public AnalogClock(Context context, AttributeSet attrs) { this(context, attrs, 0); } //在這個構造函數中加載了一些資源 public AnalogClock(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); Resources r = mContext.getResources(); TypedArray a = context.obtainStyledAttributes( attrs, com.android.internal.R.styleable.AnalogClock, defStyle, 0); mDial = a.getDrawable(com.android.internal.R.styleable.AnalogClock_dial); if (mDial == null) { mDial = r.getDrawable(com.android.internal.R.drawable.clock_dial); } mHourHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_hour); if (mHourHand == null) { mHourHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_hour); } mMinuteHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_minute); if (mMinuteHand == null) { mMinuteHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_minute); } mCalendar = new Time(); mDialWidth = mDial.getIntrinsicWidth(); mDialHeight = mDial.getIntrinsicHeight(); } //重載某些方法 @Override protected void onAttachedToWindow() { super.onAttachedToWindow(); if (!mAttached) { mAttached = true; IntentFilter filter = new IntentFilter(); filter.addAction(Intent.ACTION_TIME_TICK); filter.addAction(Intent.ACTION_TIME_CHANGED); filter.addAction(Intent.ACTION_TIMEZONE_CHANGED); getContext().registerReceiver(mIntentReceiver, filter, null, mHandler); } // NOTE: It's safe to do these after registering the receiver since the receiver always runs // in the main thread, therefore the receiver can't run before this method returns. // The time zone may have changed while the receiver wasn't registered, so update the Time mCalendar = new Time(); // Make sure we update to the current time onTimeChanged(); } @Override protected void onDetachedFromWindow() { super.onDetachedFromWindow(); if (mAttached) { getContext().unregisterReceiver(mIntentReceiver); mAttached = false; } } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { int widthMode = MeasureSpec.getMode(widthMeasureSpec); int widthSize = MeasureSpec.getSize(widthMeasureSpec); int heightMode = MeasureSpec.getMode(heightMeasureSpec); int heightSize = MeasureSpec.getSize(heightMeasureSpec); float hScale = 1.0f; float vScale = 1.0f; if (widthMode != MeasureSpec.UNSPECIFIED && widthSize < mDialWidth) { hScale = (float) widthSize / (float) mDialWidth; } if (heightMode != MeasureSpec.UNSPECIFIED && heightSize < mDialHeight) { vScale = (float )heightSize / (float) mDialHeight; } float scale = Math.min(hScale, vScale); setMeasuredDimension(resolveSize((int) (mDialWidth * scale), widthMeasureSpec), resolveSize((int) (mDialHeight * scale), heightMeasureSpec)); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); mChanged = true; } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); boolean changed = mChanged; if (changed) { mChanged = false; } int availableWidth = mRight - mLeft; int availableHeight = mBottom - mTop; int x = availableWidth / 2; int y = availableHeight / 2; final Drawable dial = mDial; int w = dial.getIntrinsicWidth(); int h = dial.getIntrinsicHeight(); boolean scaled = false; if (availableWidth < w || availableHeight < h) { scaled = true; float scale = Math.min((float) availableWidth / (float) w, (float) availableHeight / (float) h); canvas.save(); canvas.scale(scale, scale, x, y); } if (changed) { dial.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2)); } dial.draw(canvas); canvas.save(); canvas.rotate(mHour / 12.0f * 360.0f, x, y); final Drawable hourHand = mHourHand; if (changed) { w = hourHand.getIntrinsicWidth(); h = hourHand.getIntrinsicHeight(); hourHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2)); } hourHand.draw(canvas); canvas.restore(); canvas.save(); canvas.rotate(mMinutes / 60.0f * 360.0f, x, y); final Drawable minuteHand = mMinuteHand; if (changed) { w = minuteHand.getIntrinsicWidth(); h = minuteHand.getIntrinsicHeight(); minuteHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2)); } minuteHand.draw(canvas); canvas.restore(); if (scaled) { canvas.restore(); } } private void onTimeChanged() { mCalendar.setToNow(); int hour = mCalendar.hour; int minute = mCalendar.minute; int second = mCalendar.second; mMinutes = minute + second / 60.0f; mHour = hour + mMinutes / 60.0f; mChanged = true; } private final BroadcastReceiver mIntentReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { if (intent.getAction().equals(Intent.ACTION_TIMEZONE_CHANGED)) { String tz = intent.getStringExtra("time-zone"); mCalendar = new Time(TimeZone.getTimeZone(tz).getID()); } onTimeChanged(); invalidate(); } }; }
使用自定義的組件,在XML文件中像使用系統預定義的組件一樣使用
<com.android.example.CustomView android:id="@+id/customView" android:layout_height="fill_parent" android:layout_width="fill_parent" />
android 自定義組件
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