Android简单入门自定义View

自定义View的分类

1.继承View重写onDraw方法

2.继承ViewGroup派生特殊的Layout

3.继承特定的View(比如TextView)

4.继承特定的ViewGroup(比如LinearLayout)

自定义View的步骤：

1.自定义View的属性

2.在View的构造方法中获得自定义的属性

3.重写onMesure(非必需)

4.重写onDraw

1.自定义属性，首先在res/values/下建立attrs文件，并在里面定义属性

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <attr name="customText" format="string"/>
    <attr name="customTextColor" format="color"/>
    <attr name="customTextSize" format="dimension"/>

   <declare-styleable name="CustomView">
       <attr name="customText"/>
       <attr name="customTextColor"/>
       <attr name="customTextSize"/>
   </declare-styleable>


</resources>

上面定义了字体字体颜色字体大小从字面看出 format是取值类型

2.在View的构造方法中，获得自定义属性

重写三个构造方法，默认是使用两个参数的构造方法，因此让所有的构造方法调用三个参数的构造函数

public class CustomView extends View {

    //文本
    private String mCustomText;
    //文本颜色
    private int mCustomTextColor;
    //文本大小
    private int mCustomTextSize;

    //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(Context context,AttributeSet attrs,int defstyle){
        super(context,attrs,defstyle);
        //获取自定义的自定义样式
        TypedArray ta  = context.getTheme().obtainStyledAttributes(attrs, R.styleable.CustomView,defstyle,0);
        //获取有多少个属性
        int n = ta.getIndexCount();

        for(int i=0;i < n;i++){
            int attr = ta.getIndex(i);//获取具体的属性值

            switch(attr){
                case R.styleable.CustomView_customText:
                    mCustomText = ta.getString(attr);
                    break;
                case R.styleable.CustomView_customTextColor:
                    mCustomTextColor = ta.getColor(attr, Color.RED);
                    break;
                case R.styleable.CustomView_customTextSize:
                    mCustomTextSize = ta.getDimensionPixelSize(attr,(int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP,16,getResources().getDisplayMetrics()));
                    break;

            }

        }
        ta.recycle();

        //获得绘制文本的宽高
        mPaint = new Paint();
        mPaint.setTextSize(mCustomTextSize);
        mBound = new Rect();
        mPaint.getTextBounds(mCustomText,0,mCustomText.length(),mBound);
    }


}

3.重写onDraw,onMesure方法

@Override
    protected void onMeasure( int widthMeasureSpec, int heightMeasureSpec){
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

    }

    @Override
    protected void onDraw(Canvas canvas)
    {
        //设置背景
        mPaint.setColor(Color.BLACK);
        canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), mPaint);

        mPaint.setColor(mCustomTextColor);
        canvas.drawText(mCustomText, getWidth() / 2 - mBound.width() / 2, getHeight() / 2 + mBound.height() / 2, mPaint);
    }

4.在布局文件声明自定义view

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:custom="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.nova.customviewdemo.ui.MainActivity">

    <com.nova.customviewdemo.view.CustomView
        android:layout_width="120dp"
        android:layout_height="100dp"
        custom:customText="1111"
        custom:customTextColor="#ff0000"
        custom:customTextSize="40sp"
        />

</RelativeLayout>

此时的效果是:

就这样一个带文字的矩形就描绘出来了

Android简单入门自定义View

自定义View的分类

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