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我正在嘗試創建一個Android應用程序，用戶可以將任何圓圈拖過另一個圓圈，文本框應顯示這兩個圓圈的總和。每次程序啓動時，它應該顯示從1到9的隨機位置和隨機數的圓圈。Android中可拖動的圓圈內的文本
不幸的是，我不是靠近那個目標的地方，我創建了一個圓圈，但是當我嘗試拖動它時，應用程序崩潰。請同時幫助我完成應用程序的其他功能。謝謝。
最終的輸出應該是這個樣子： 
MainActivity.java
package com.dragandadd;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MotionEvent;
import android.view.View;
import android.widget.FrameLayout;
public class MainActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FrameLayout main = (FrameLayout) findViewById(R.id.activity_main);
main.addView(new Ball(this,50,50,25));
main.addView(new Ball(this,50,50,25));
main.setOnTouchListener(new View.OnTouchListener() {
public boolean onTouch(View v, MotionEvent e) {
float x = e.getX();
float y = e.getY();
FrameLayout flView = (FrameLayout) v;
flView.addView(new Ball(getParent(), x,y,25));
return true;
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}
Ball.java
package com.dragandadd;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.view.View;
public class Ball extends View {
final float x;
final float y;
final int r;
final Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
public Ball(Context context, float x, float y, int r) {
super(context);
mPaint.setColor(0xFFFF0000);
this.x = x;
this.y = y;
this.r = r;
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawCircle(x, y, r, mPaint);
}
}
activity_main
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/activity_main"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#FF66FF33" />