getWidth 和 getHeight 返回零 [英] getWidth and getHeight are returning a zero

问题描述

我正在尝试为 android 制作一个简单的绘图程序.

I am trying to make a simple drawing program for the android.

我有一个自定义的 View 类来处理绘图.当我调用它的 getWidth 和 getHeight 方法时，我得到一个零.

I have a custom View class to handle the drawing. When I call its getWidth and getHeight metheds, I get a zero.

但是，绘图效果很好，我对宽度和高度进行了硬编码，因此可以正常工作.为什么要这样做?

But, the drawing works fine, I hard code in the width and height so it works. Why is it doing this?

我的视图类

public class cDrawing extends View{

    char BitMap[];
    static final short WIDTH=160;
    static final short HEIGHT=440;
    static final char EMPTY=' ';
    int mWidthSize;
    int mHeightSize;

    static final char RED ='R';
    int y;

    public cDrawing(Context context) {
        super(context);

        y=3;
        // set up our bitmap
        BitMap=new char[WIDTH*HEIGHT];
        for(int i=0; i<WIDTH*HEIGHT; i++)
                BitMap[i]=EMPTY;


        // returns zero why???????
        int h=getHeight();
        h=400;
        int w=getWidth();
        w=320;
        mWidthSize=w/WIDTH;
        mHeightSize=h/HEIGHT;


        // TODO Auto-generated constructor stub
    }

<小时>

活动类

public class cCanves extends Activity  implements OnClickListener {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.canves);
        cDrawing board=new cDrawing(this);


        LinearLayout layout = (LinearLayout)findViewById(R.id.parent2);
        layout.addView(board);


        // set up buttons
        View mEraser = findViewById(R.id.buteraser);
        mEraser.setOnClickListener(this);

        View mBlack = findViewById(R.id.butblack);
        mBlack.setOnClickListener(this);

        View mWhite = findViewById(R.id.butwhite);
        mWhite.setOnClickListener(this);

        View mRed = findViewById(R.id.butred);
        mRed.setOnClickListener(this);

    } // end function

    public void onClick(View v) {
        Intent i;
        switch(v.getId())
        {
        case R.id.buteraser:
            break;
        case R.id.butblack:
            break;
        case R.id.butwhite:
            break;
        case R.id.butred:
            break;
        } // end switch

    }   // function
}

<小时>

xml 文件

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

    <LinearLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="wrap_content"
      android:orientation="horizontal"
      android:layout_height="wrap_content">

    <ImageButton android:id="@+id/buteraser"
      android:src="@drawable/icon"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"/>

    <ImageButton android:id="@+id/butblack"
      android:src="@drawable/icon"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"/>

    <ImageButton android:id="@+id/butwhite"
      android:src="@drawable/icon"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"/>

    <ImageButton android:id="@+id/butred"
      android:src="@drawable/icon"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"/>
    </LinearLayout>

    <LinearLayout android:id="@+id/parent2"
      android:layout_width="fill_parent"
      android:orientation="vertical"
      android:layout_height="fill_parent">
    </LinearLayout>


</LinearLayout>

推荐答案

直到视图实际呈现到屏幕上时才定义宽度和高度.

The width and height are not defined until the view is actually rendered to the screen.

使用 protected abstract void onLayout (boolean changed, int l, int t, int r, int b)(您在活动中覆盖)以了解尺寸何时准备就绪.

Use protected abstract void onLayout (boolean changed, int l, int t, int r, int b) (which you override in your activity) to know when the sizes are ready.

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