Android 自定义 View 实例 随手拖动小球

ViewTest.java

package com.toby.personal.datatypeconverttest;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by TT on 2017/1/15.
 */

public class ViewTest extends View {

    public float currentX = 200;
    public float currentY = 200;

    Paint paint = new Paint();

    public ViewTest(Context context) {
        super(context);
    }

    public ViewTest(Context context, AttributeSet set) {
        super(context, set);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        paint.setColor(Color.RED);
        paint.setAntiAlias(true);
        canvas.drawCircle(currentX, currentY, 180, paint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        currentX = event.getX();
        currentY = event.getY();

        invalidate();

        return true;
    }
}

activity_main.xml

MainActivity.java

package com.toby.personal.datatypeconverttest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}