如何使用视图扩展类的canvas进入活动类？

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();
    }
}

现在我从活动中调用该类:

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插入活动类并设置为ImageView.我该怎么做？

Answer 1

您需要继承自己的类View并覆盖onDraw()和onMeasure().就像你开始做的那样TestCanvas.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);
    }
}

将自定义视图添加到活动的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>

您的活动课程没有任何内容.而已!

如果您确实需要使用ImageView:继承您的自定义视图ImageView而不是View.然后用自定义的ImageView替换您的活动的布局XML适当的ImageView的标签,如com.yourapphere.MyImageView)

参考和链接
看到类似的问题:如何在android中的imageview上绘制画布
简单的自定义视图示例代码:将我的自定义视图添加到XML布局会引发异常

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