自定义view是安卓开发进阶中的重要阶段。所以想在这方面多花些时间看看，写写。
自定义view的步骤：
1、自定义View的属性
2、在View的构造方法中获得我们自定义的属性
3、重写onMesure
4、重写onDraw
1、自定义View的属性，首先在res/values/ 下建立一个attrs.xml ， 在里面定义我们的属性和声明我们的整个样式。
<?xml version="1.0" encoding="utf-8"?>
<resources>
<attr name="text" format="string"/>
<attr name="textsize" format="dimension"/>
<attr name="textcolor" format="color"/>
<declare-styleable name="CustomView">
<attr name="text"/>
<attr name="textsize"/>
<attr name="textcolor"/>
</declare-styleable>
</resources>
定义了字体，字体颜色，字体大小3个属性，format是值该属性的取值类型;
2、创建自定义View继承view ，在构造方法中，获得我们的自定义的样式
/**
* 自定义View
* Created by zzj on 2016/11/14.
*/
public class CustomView extends View {
private static final String TAG = "customview";
private String mTitleText;
/**
* 文本的颜色
*/
private int mTitleTextColor;
/**
* 文本的大小
*/
private int mTitleTextSize;
/**
* 绘制时控制文本绘制的范围
*/
private Rect mBound;
private Paint mPaint;
public CustomView(Context context) {
this(context,null);
}
public CustomView(Context context, AttributeSet attrs) {
this(context, attrs,0);
}
public CustomView(final Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
/**
* 获得我们所定义的自定义样式属性
*/
TypedArray a = context.getTheme().obtainStyledAttributes(attrs, R.styleable.CustomView, defStyleAttr, 0);
int n = a.getIndexCount();
for (int i = 0; i < n; i++)
{
int attr = a.getIndex(i);
switch (attr)
{
case R.styleable.CustomView_text:
mTitleText = a.getString(attr);
break;
case R.styleable.CustomView_textcolor:
// 默认颜色设置为黑色
mTitleTextColor = a.getColor(attr, Color.BLACK);
break;
case R.styleable.CustomView_textsize:
// 默认设置为16sp，TypeValue也可以把sp转化为px
mTitleTextSize = a.getDimensionPixelSize(attr, (int) TypedValue.applyDimension(
TypedValue.COMPLEX_UNIT_SP, 16, getResources().getDisplayMetrics()));
break;
}
}
a.recycle();
/**
* 获得绘制文本的宽和高
*/
mPaint = new Paint();
mPaint.setTextSize(mTitleTextSize);
// mPaint.setColor(mTitleTextColor);
mBound = new Rect();
mPaint.getTextBounds(mTitleText, 0, mTitleText.length(), mBound);
//添加点击事件
this.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
Toast.makeText(context,TAG,Toast.LENGTH_SHORT).show();
}
});
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
Log.d(TAG,"onMeasure----------");
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
Log.d(TAG,"widthMode:"+widthMode+"widthSize:"+widthSize+"heightMode:"+heightMode+"heightSize:"+heightSize);
int width;
int height ;
if (widthMode == MeasureSpec.EXACTLY)
{
width = widthSize;
} else
{
mPaint.setTextSize(mTitleTextSize);
mPaint.getTextBounds(mTitleText, 0, mTitleText.length(), mBound);
float textWidth = mBound.width();
int desired = (int) (getPaddingLeft() + textWidth + getPaddingRight());
width = desired;
}
if (heightMode == MeasureSpec.EXACTLY)
{
height = heightSize;
} else
{
mPaint.setTextSize(mTitleTextSize);
mPaint.getTextBounds(mTitleText, 0, mTitleText.length(), mBound);
float textHeight = mBound.height();
int desired = (int) (getPaddingTop() + textHeight + getPaddingBottom());
height = desired;
}
setMeasuredDimension(width, height);
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
Log.d(TAG,"onLayout----------");
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.d(TAG,"onDraw----------");
mPaint.setColor(Color.YELLOW);
canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), mPaint);
mPaint.setColor(mTitleTextColor);
canvas.drawText(mTitleText, getWidth() / 2 - mBound.width() / 2, getHeight() / 2 + mBound.height() / 2, mPaint);
}
}
我们重写了3个构造方法，默认的布局文件调用的是两个参数的构造方法，所以记得让所有的构造调用我们的三个参数的构造，我们在三个参数的构造中获得自定义属性。重写了onMeasure和onDraw方法
onMeasure方法：
系统帮我们测量的高度和宽度都是MATCH_PARNET，当我们设置明确的宽度和高度时，系统帮我们测量的结果就是我们设置的结果，当我们设置为WRAP_CONTENT,或者MATCH_PARENT系统帮我们测量的结果就是MATCH_PARENT的长度。
所以，当设置了WRAP_CONTENT时，我们需要自己进行测量，即重写onMesure方法”；
在onDraw方法中进行绘制；
3.然后在布局中声明我们的自定义View
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.zzj.customview.MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!" />
<com.zzj.customview.views.CustomView
android:id="@+id/customview"
android:layout_width="300dp"
android:layout_height="100dp"
app:textcolor="@color/colorPrimary"
app:textsize="30dp"
app:text="78945620"
/>
</RelativeLayout>
运行效果：
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