Android的画布的drawLine不是MainActivity画 [英] Android Canvas drawLine not drawing on MainActivity

问题描述

我想提请使用画布的主要活动线路。的问题是，它没有画什么。我有以下的code：

 位图位= Bitmap.createBitmap（1920，1080，Bitmap.Config.ARGB_8888）;

帆布油画=新的Canvas（位）;
涂料粉刷=新的油漆（）;
paint.setColor（Color.BLACK）;
paint.setStyle（Paint.Style.FILL_AND_STROKE）;
paint.setStrokeWidth（10）;

左浮动= 20;
浮顶= 20;
浮动权= 50;
浮底= 100;

canvas.drawLine（左，上，右，下，涂料）;
 

解决方案

您可以显示这样的位图：

  canvas.drawBitmap（BMP，位X，positionY，油漆）;
 

在你的情况，你可以试试财产以后像这样的：

  canvas.drawBitmap（位图，0，0，NULL）;
 

但你需要使用不同势帆布它。画布至极，让你画的东西在你的屏幕将被传递给你的OnDraw（）方法，在你的视图。所以，你需要做一个视图类第一，并在您MainActivity添加它。

您可以做到这一点是这样的： 首先创建一个类MyView的，并添加这个code到它：

 公共类MyView的扩展视图{

    点阵位图;

    公共MyView的（上下文的背景下）{
        位图= Bitmap.createBitmap（1920，1080，Bitmap.Config.ARGB_8888）;

        帆布油画=新的Canvas（位）;
        涂料粉刷=新的油漆（）;
        paint.setColor（Color.BLACK）;
        paint.setStyle（Paint.Style.FILL_AND_STROKE）;
        paint.setStrokeWidth（10）;

        左浮动= 20;
        浮顶= 20;
        浮动权= 50;
        浮底= 100;

        canvas.drawLine（左，上，右，下，涂料）;
    }

    @覆盖
    保护无效的OnDraw（帆布油画）{
        canvas.drawBitmap（位图，0，0，NULL）;
        super.onDraw（画布）;
    }
}
 

然后你在MainActivity改变code在你的onCreate（）方法，以这样的：

  @覆盖
保护无效的onCreate（包savedInstanceState）{
    super.onCreate（savedInstanceState）;

    MyView的MyView的=新的MyView的（这一点）;
    的setContentView（MyView的）;
}
 

I want to draw a line on the Main Activity using Canvas. The problem is, it is not drawing anything. I have the following code:

 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);

解决方案

you can display the bitmap like that:

canvas.drawBitmap(bmp, positionX, positionY, paint);

in your case you can try somthing like this:

canvas.drawBitmap(bitmap, 0, 0, null);

but you need to use a diffrent canvas for it. The canvas wich let you draw stuff on your screen will be passed to your onDraw() method in your View. So you need to make a View class first and add it in your MainActivity.

You can do that like this: First you create a class called MyView and add this code to it:

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);
    }
}

then you change the code in your onCreate() method in your MainActivity to this:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);  

    MyView myView = new MyView(this);
    setContentView(myView);
}

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