android - 如何将 View 扩展类的 Canvas 用于 Activity 类？

Question

我创建了一个类:

public class TestCanvas extends View {

    public TestCanvas(Context context) {
        super(context);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = new Paint();
        paint.setColor(Color.RED);

        canvas.drawText("kal", 0, 100, paint);
        canvas.save();
    }
}

现在我从 Activity 中调用那个类:

public class TestActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        TestCanvas tcanvas=new TestCanvas();

        frameLayout=(FrameLayout)findViewById(R.id.frameLayout1);
        frameLayout.addView(tcanvas);   
    }
}

现在我想将 Canvas 放入 Activity 类中并设置为 ImageView。我该怎么做？

Answer 1

您需要从View 继承您自己的类并覆盖onDraw() 和onMeasure()。就像您开始使用 TestCanvas 一样。一个例子:

package com.yourapphere;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.util.AttributeSet;
import android.view.View;

public class TwoDee extends View {
    private int mWidth;
    private int mHeight;


    public TwoDee(Context context) {
        super(context);
    }

    public TwoDee(Context context, AttributeSet attribs) {
        super(context, attribs);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = new Paint(); 
        paint.setColor(Color.GRAY); 
        paint.setStyle(Style.FILL); 
        canvas.drawPaint(paint);

        paint.setColor(Color.BLUE);
        canvas.drawLine(0, 0, mWidth, mHeight, paint);
        canvas.drawLine(mWidth, 0, 0, mHeight, paint);

        paint.setColor(Color.RED);
        canvas.drawText("0 kal", 50, 85, paint);
        canvas.save();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        mWidth = View.MeasureSpec.getSize(widthMeasureSpec);
        mHeight = View.MeasureSpec.getSize(heightMeasureSpec);
        setMeasuredDimension(mWidth, mHeight);
    }
}

将自定义 View 添加到 Activity 的 xml 布局中，如下所示。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
        <TextView  
            android:layout_width="fill_parent" 
            android:layout_height="wrap_content" 
            android:text="@string/hello"
        />
        <com.yourapphere.TwoDee
            android:layout_width="150dp"
            android:layout_height="100dp"
        />
</LinearLayout>

您的 Activity 类(class)中没有任何内容。就是这样!

如果您确实需要使用 ImageView:从 ImageView 而不是 View 继承您的自定义 View 。然后用自定义 ImageView 替换 Activity 布局 xml 中的适当 ImageView 标签，例如 com.yourapphere.MyImageView)

引用和链接
查看类似问题:How to take canvas on imageview in android
简单的自定义 View 示例代码:Adding my custom View into an XML layout throws exception

阅读有关 Android 2D 绘图的信息:http://developer.android.com/guide/topics/graphics/2d-graphics.html
Android二维编码教程:http://www3.ntu.edu.sg/home/ehchua/programming/android/Android_2D.html
简单的2D游戏教程:http://www.barebonescoder.com/2010/06/android-development-simple-2d-graphics-part-1/