Android开发-自定义View-AndroidStudio(十一)有趣的BUG

package com.iwanghang.scrolltest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

package com.iwanghang.scrolltest;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;

public class MyImageView extends View {

    private GestureDetector detector; // 定义手势识别类
    private Bitmap image;
    private int lastX;
    private int lastY;

    public MyImageView(Context context, AttributeSet attrs) {
        super(context, attrs);

        // 使用系统工具，获取属性
        TypedArray typedArray = context.obtainStyledAttributes(attrs,R.styleable.MyAttributeView);
        for (int i = 0; i <typedArray.getIndexCount() ; i++) {
            int index = typedArray.getIndex(i);

            switch (index){
                  case R.styleable.MyAttributeView_my_image:
                    Drawable drawable = typedArray.getDrawable(index);
                    BitmapDrawable drawable1 = (BitmapDrawable) drawable;
                    image = drawable1.getBitmap();
                    break;
            }
        }
            // 记得回收
            typedArray.recycle();

            initView(context); // 实例化手势识别类
    }

    /**
     * 实例化手势识别类
     */
    private void initView(Context context) {
        detector = new GestureDetector(context,new GestureDetector.SimpleOnGestureListener(){
            @Override
            public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
                scrollBy((int)distanceX, (int)distanceY); // 可以上下左右滑动
                return true;
            }
        });
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        super.onTouchEvent(event);
        // 把时间传递给手势识别器
        detector.onTouchEvent(event);


        //获取到手指处的横坐标和纵坐标
        int x = (int) event.getX();
        int y = (int) event.getY();

        switch(event.getAction())
        {
            case MotionEvent.ACTION_DOWN:
                lastX = x;
                lastY = y;
                break;
            case MotionEvent.ACTION_MOVE:
                //计算移动的距离
                int offX = x - lastX;
                int offY = y - lastY;
                //调用layout方法来重新放置它的位置
                layout(getLeft()+offX, getTop()+offY, getRight()+offX, getBottom()+offY);
                break;
        }

        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        canvas.drawBitmap(image,null, new Rect(0,0,100,100),null);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="MyAttributeView">
        <attr name="my_image" format="reference|color"/>
    </declare-styleable>
</resources>

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:iwanghang="http://schemas.android.com/apk/res-auto"
    tools:context="com.iwanghang.scrolltest.MainActivity">

    <TextView
        android:textColor="#ff0000"
        android:textSize="20sp"
        android:text="见证奇迹的时候到了......"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <com.iwanghang.scrolltest.MyImageView
        android:id="@+id/iv_main"
        android:background="@drawable/bg_red"
        iwanghang:my_image="@mipmap/ic_launcher"
        android:layout_width="200dp"
        android:layout_height="200dp" />

</RelativeLayout>

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