Question

我已经开始学习为Android OS开发应用程序。我想在用户点击按钮后绘制一个圆圈。我的MainActivity看起来像：

public class MainActivity extends Activity {
EditText editText;
String message;
TextView display;
ImageView transOutput;
Paint paint;
Canvas c;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    editText = (EditText) findViewById(R.id.editText1);
    //display = (TextView)findViewById(R.id.display);

    Button basic_button = (Button) findViewById(R.id.button1);
    basic_button.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            c = new Canvas();
            c.drawColor(Color.CYAN);
                // smooths
            paint = new Paint();
            paint.setAntiAlias(true);
            paint.setColor(Color.RED);
            paint.setStyle(Paint.Style.STROKE); 
            paint.setStrokeWidth(4.5f);
                // opacity
                //p.setAlpha(0x80); //
            c.drawCircle(50, 50, 30, paint);

        }
    }); 
}

我认为将绘图函数放在onClick侦听器中就可以了。最终我将添加更多形状。我错过了什么？

Answer 1

如果你需要创建一个新的Canvas，那么你必须定义实际绘图的Bitmap。

Bitmap b = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(b);

http://developer.android.com/guide/topics/graphics/2d-graphics.html

单击Android按钮后绘制

1 个答案: