Android canvas+paint绘制一个可以指定位置移动的小球（含触屏响应）

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <EditText
        android:id="@+id/txt_1"
        android:layout_width="200dp"
        android:layout_height="wrap_content"/>
    <Button
        android:id="@+id/but_1"
        android:text="确认"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
        <com.android.canvstest.TestView
            android:layout_height="wrap_content"
            android:id="@+id/textview1"
            android:layout_width="wrap_content"/>
</LinearLayout>

package com.android.canvstest;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;


public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final TestView testView = findViewById(R.id.textview1);
        Button button = findViewById(R.id.but_1);
        final EditText editText = findViewById(R.id.txt_1);
        testView.setXY(100,100);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int x=100;
                x = Integer.parseInt(editText.getText().toString());
                testView.setXY(x,100);
                testView.invalidate();
            }
        });
    }

}

自定义TextView

package com.android.canvstest;

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

import androidx.annotation.Nullable;

public class TestView extends View {

    int x,y;

    public TestView(Context context, @Nullable AttributeSet attrs) {    //必须使用AttributeSet接口做对象的参数
        super(context, attrs);
    }


    void setXY(int x1,int y1){
        x=x1;
        y=y1;
    }

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

        Paint paint=new Paint();
        paint.setAntiAlias(true);
        paint.setColor(Color.GREEN);
        paint.setStyle(Paint.Style.FILL);

        canvas.drawCircle(x,y,50,paint);
        paint.setColor(Color.RED);
        canvas.drawCircle(x,y,10,paint);

    }
}

 后面我又写了一下触屏移动操作（只需要改动MainActivity）：

package com.android.canvstest;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;


public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final TestView testView = findViewById(R.id.textview1);
        Button button = findViewById(R.id.but_1);
        final EditText editText = findViewById(R.id.txt_1);
        testView.setXY(100, 100);

        testView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                int x,y;
                x = (int) event.getX();
                y = (int) event.getY();
                if (event.getAction() == MotionEvent.ACTION_DOWN){
                    testView.setXY(x,y);
                    testView.invalidate();
                    return true;
                }
                else if (event.getAction() == MotionEvent.ACTION_MOVE){
                    testView.setXY(x,y);
                    testView.invalidate();
                    return true;
                }
                return testView.onTouchEvent(event);
            }
        });
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int x=100;
                x = Integer.parseInt(editText.getText().toString());
                testView.setXY(x,100);
                testView.invalidate();
            }
        });
    }
}