android自定义控件

自定义一个控件，继承自ImageView

1、覆写ImageView的三个构造函数

2、覆写onDraw() 方法，利用canvas重绘想展示的界面

3、在布局文件中声明该控件，需要加上包名

在布局文件中的声明

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/line"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"> 
  <com.android.activity.MatrixTransImageView
        android:id="@+id/myImageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#000000"
        android:src="@drawable/ic_launcher"
        android:gravity="center"
/>
</LinearLayout>

继承类

package com.android.activity;  
import android.content.Context;  
import android.graphics.Bitmap;  
import android.graphics.BitmapFactory;  
import android.graphics.Canvas;  
import android.graphics.Matrix;  
import android.util.AttributeSet;  
import android.widget.ImageView;  
public class MatrixTransImageView extends ImageView    
{      
    private Bitmap bitmap;    
    private Matrix matrix;     
    public MatrixTransImageView(Context context) {  
        super(context);  
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);    
        matrix = new Matrix();          
    }     
    public MatrixTransImageView(Context context, AttributeSet attrs) {  
       super(context,attrs);  
       bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);    
       matrix = new Matrix();    
    }  
      
    public MatrixTransImageView(Context context, AttributeSet attrs, int defStyle) {  
        super(context, attrs, defStyle);  
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);    
        matrix = new Matrix();       
      
    }   
      
  //该方法在控件显示在activity中时自动调用  
    @Override    
    protected void onDraw(Canvas canvas)    
    {    
        //在（100,100）处显示ic_lanucher  
        canvas.drawBitmap(bitmap, 100, 100, null);   
        super.onDraw(canvas);             
    } }