我想使用Canvas在主要活动上画一条线。问题是,它没有绘制任何东西。我有以下代码:
Bitmap bitmap = Bitmap.createBitmap(1920, 1080, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
Paint paint = new Paint();
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.FILL_AND_STROKE);
paint.setStrokeWidth(10);
float left = 20;
float top = 20;
float right = 50;
float bottom = 100;
canvas.drawLine(left, top, right, bottom, paint);
答案 0 :(得分:4)
你可以像这样显示位图:
canvas.drawBitmap(bmp, positionX, positionY, paint);
在你的情况下,你可以尝试这样的事情:
canvas.drawBitmap(bitmap, 0, 0, null);
但你需要使用不同的画布。允许您在屏幕上绘制内容的画布将传递到视图中的onDraw()方法。因此,您需要先创建一个View类,然后将其添加到MainActivity中。
你可以这样做: 首先,您创建一个名为MyView的类,并将此代码添加到其中:
public class MyView extends View {
Bitmap bitmap;
public MyView(Context context) {
bitmap = Bitmap.createBitmap(1920, 1080, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
Paint paint = new Paint();
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.FILL_AND_STROKE);
paint.setStrokeWidth(10);
float left = 20;
float top = 20;
float right = 50;
float bottom = 100;
canvas.drawLine(left, top, right, bottom, paint);
}
@Override
protected void onDraw(Canvas canvas) {
canvas.drawBitmap(bitmap, 0, 0, null);
super.onDraw(canvas);
}
}
然后将MainActivity中onCreate()方法中的代码更改为:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
MyView myView = new MyView(this);
setContentView(myView);
}
答案 1 :(得分:1)
创建一个这样的类
public class MyView extends View {
public MyView(Context context) {
super(context);
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
protected void onDraw(Canvas canvas) {
Paint paint = new Paint();
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.FILL_AND_STROKE);
paint.setStrokeWidth(10);
float left = 20;
float top = 20;
float right = 50;
float bottom = 100;
canvas.drawLine(left, top, right, bottom, paint);
}
}