自定义View

为什么要自定义view

在实际项目中安卓的view无法满足特定的需求，所以需要扩展或者修改原生view，满足特定需求。

安卓系统自带view结构

1.view类是layout和view容器的基类，这个类包含了所有的屏幕类型。
2.layout和view容器是安卓SDK封装好的基础组件，例如button，listview等控件和LinearLayout等布局容器

自定义view的定义

通过直接继承view或重写view子类，实现逻辑的view，称之为自定义为view。

如何使用自定义view

1.直接继承view类式的方式自绘控件
2.简洁继承view类式的方式重写控件
3.间接继承view子类，将需要用到的原生控件组合到一起

自绘控件的步骤

1.继承view
2.实现listener接口
3.重写构造方法
4.重写onDraw方法
5.paint 画笔
6.Canvas 绘制
7.invalidate方法刷新
8.在布局文件中引用

实现计数器

先新建一个myview的类继承View，然后实现画圆和写字的功能，最后在onTouchEvent里面使用invalidate方法，然后在调用onDraw方法。

public class MyView extends View {

    private Paint paint = new Paint();
    private int num = 0;


    public MyView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);

    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //实现画圆功能
        paint.setColor(Color.RED);
        paint.setAntiAlias(true);
        canvas.drawCircle(getWidth() / 2, getHeight() / 2, getWidth() / 4, paint);

        //实现写字功能
        paint.setColor(Color.GREEN);
        paint.setTextSize(50);
        canvas.drawText(num + "", getWidth() / 2 - 15, getHeight() / 2 + 25, paint);


    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        num++;

        invalidate();//点击一次，调用onDraw方法

        return super.onTouchEvent(event);
    }
}

最后引用布局

<?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"
    tools:context="myapplication.com.example.viewdemo.MainActivity">

   <myapplication.com.example.viewdemo.MyView
       android:layout_width="match_parent"
       android:layout_height="wrap_content" />

</RelativeLayout>

实现模拟时钟

     新建一个clickview继承view，然后定义一个paint画笔，先用画笔写一个数字，然后去除锯齿，用画布画东西时，需要先保存画布，最后在restore。接着定义一个second，在onTouchEvent里面写一个子线程，实现run的方法。然后通过子线程传递信息给主线程，在主线程里面实现  invalidate方法（子线程不能更新UI）。

获取本地时间和秒针时针，其实和获取分针是类似的方法。但是最后handler就不需要了。

public class ClickView extends View {

    private Paint paint = new Paint();



/*
    public Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            invalidate();
        }
    };*/


    public ClickView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);

    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        paint.setColor(Color.BLUE);
        paint.setStyle(Paint.Style.STROKE);
        paint.setAntiAlias(true);
        paint.setStrokeWidth(10);
        canvas.drawCircle(getWidth() / 2, getHeight() / 2, getWidth() / 3, paint);


        paint.setStyle(Paint.Style.FILL);
        paint.setStrokeWidth(2);
        paint.setTextSize(20);

        for (int i = 1; i <= 12; i++) {
            canvas.save();
            canvas.rotate(30 * i, getWidth() / 2, getHeight() / 2);

            canvas.drawLine(getWidth() / 2, getHeight() / 2 - getWidth() / 3, getWidth() / 2, getHeight() / 2 - getWidth() / 3 + 20, paint);
            canvas.drawText(i + "", getWidth() / 2 - 10, getHeight() / 2 - getWidth() / 3 + 40, paint);
            canvas.restore();
        }

        Calendar calendar = Calendar.getInstance();
        int hour = calendar.get(Calendar.HOUR);
        int minute = calendar.get(Calendar.MINUTE);
        int second = calendar.get(Calendar.SECOND);


        canvas.save();
        canvas.rotate(6 * second, getWidth() / 2, getHeight() / 2);
        canvas.drawLine(getWidth() / 2, getHeight() / 2, getWidth() / 2, getHeight() / 2 - getWidth() / 3 + 50, paint);
        canvas.restore();


        canvas.save();
        canvas.rotate(minute * 6, getWidth() / 2, getHeight() / 2);
        paint.setColor(Color.RED);
        canvas.drawLine(getWidth() / 2, getHeight() / 2, getWidth() / 2, getHeight() / 2 - getWidth() / 3 + 60, paint);
        canvas.restore();


        canvas.save();
        canvas.rotate(hour * 30 + minute * 30 / 60, getWidth() / 2, getHeight() / 2);
        paint.setColor(Color.BLUE);
        canvas.drawLine(getWidth() / 2, getHeight() / 2, getWidth() / 2, getHeight() / 2 - getWidth() / 3 + 80, paint);
        canvas.restore();

        invalidate();

    }



  /*//  @Override
  //  public boolean onTouchEvent(MotionEvent event) {

    //    new Thread(new Runnable() {
    //        @Override
   //         public void run() {
     //           while (secDegree<40){
                    secDegree++;

                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    handler.sendEmptyMessage(secDegree);
                }

            }
        }).start();

        return super.onTouchEvent(event);

    }
*/
}

 最后引用布局

<?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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="myapplication.com.example.viewdemo.ClickActivity">

    <myapplication.com.example.viewdemo.ClickView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />
</RelativeLayout>