java - 无法创建自定义 Canvas View 的多个实例，并且无法将输入值传递给 Canvas 函数 -Android

Question

我遇到一个问题，无法在多个位置创建自定义用户界面的多个实例。并且无法将输入发送到 Mycanvas 进行进一步的 UI 修改。

MyCanvas 类:

public class MyCanvas extends View {
     private int total;
     private int width;
     private int height;

     @Override
     public void onDraw(Canvas canvas){
        // Drawing my stuff here with (width and height gives me 0 here)
        if(total == 50 || total == 150){ total == 100;}
    }
     public int addToCanvas(int value){ total += value ;}
     public int subtractToCanvas(int value){ total -= value ;}

     //All three of contructors here
     public MyCanvas(Context context) {
       super(context);
       total = 100;
       width = getWidth();
       height = getHeight();
     }

     public MyCanvas(Context context, AttributeSet attrs) {
        super(context, attrs);
        total = 100;
        width = getWidth();
        height = getHeight();
     }

    public MyCanvas(Context context, AttributeSet attrs, int defStyleAttr) {
       super(context, attrs, defStyleAttr);
       total = 100;
       width = getWidth();
       height = getHeight();
    }
}

主要 Activity 类别:

public class MainActivity extends Activity {

    private MyCanvas mycanvas;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mycanvas= (MyCanvas) findViewById(R.id.customcanvas);
        mycanvas.addToCanvas(10);
    }
}

主要 Activity XML:

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:orientation="vertical" >  

    <Button android:id="@+id/bTest"
        android:layout_width="wrap_content"     
        android:layout_height="wrap_content"
        android:text="Button" />    

    <com.example.me.MyCanvas android:id="@+id/customcanvas"
        android:layout_width="wrap_content"     
        android:layout_height="wrap_content" />  
</RelativeLayout> 

我想要的只是在具有不同实例的多个地方使用我的默认 Canvas ，就像进度栏一样..

Answer 1

主要问题似乎是您太早尝试获取有关 View 尺寸的信息。据我所知，最好的时间是在“onDraw()”方法中分别调用“getMeasuredHeight()”和“getMeasuredWidth()”。

编辑:

为了获得一个工作示例，我通过添加 Paint 和初始化它的方法以及“onDraw()”方法中的一些代码来更改“MyCanvas”。

public class MyCanvas extends View
{
private int total;
private int width;
private int height;

private Paint paintLine;

public void init()
{
    // call this from all of the constructors
    paintLine = new Paint();
    paintLine.setStyle(Paint.Style.STROKE); // linie
    paintLine.setColor(Color.rgb(0, 40, 80));
    paintLine.setStrokeWidth(2.0f); // strichbreite
    paintLine.setAntiAlias(true);
}

@Override
public void onDraw(Canvas canvas){
    // Drawing my stuff here with (width and height gives me 0 here)

    // use 'getMeasuredWidth()' and 'getMeasuredHeight()' here!
    // calling 'getWidth()' and 'getHeight()' in the constructor is too early,
    // the View is not yet laid out.
    width = getMeasuredWidth();
    height = getMeasuredHeight();

    canvas.drawCircle(width/2.0f, height/2.0f, (total / 100f) * (width + height)/8.0f, paintLine);

    // this won't compile:
    //if(total == 50 || total == 150){ total == 100;}
    if(total == 50 || total == 150){ total = 100;}
}


public int addToCanvas(int value)
{ total += value ;
    // you need to return something!
    return total;
}
public int subtractToCanvas(int value)
{ total -= value ;
    // same here
    return total;
}

//All three of contructors here
public MyCanvas(Context context) {
    super(context);
    total = 100;
//    width = getWidth();
//    height = getHeight();
    init();
}

public MyCanvas(Context context, AttributeSet attrs) {
    super(context, attrs);
    total = 100;
//    width = getWidth();
//    height = getHeight();
    init();
}

public MyCanvas(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    total = 100;
 //   width = getWidth();
 //   height = getHeight();
    init();
}
}

MainActivity，出于测试驱动目的而更改:

public class MainActivity extends Activity
{

private MyCanvas mycanvas;
private Button myButton;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    myButton = (Button)findViewById(R.id.bTest);
    myButton.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View v)
        {
            mycanvas.addToCanvas(10);
            mycanvas.invalidate();
        }
    });
    mycanvas= (MyCanvas) findViewById(R.id.customcanvas);
    mycanvas.addToCanvas(10);
}
}