android图片拖动并限制区域

古城微笑少年丶 2023-01-02 07:29 155阅读 0赞

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布局文件activity\_main.xml

处理Activity类

package com.hbk.motionevent;
    
    import android.app.Activity;
    import android.os.Bundle;
    import android.view.MotionEvent;
    import android.view.View;
    import android.view.View.OnTouchListener;
    import android.widget.ImageView;
    import android.widget.RelativeLayout;
    
    public class MainActivity extends Activity implements OnTouchListener { 
    
    	private ImageView iv_main;
    	private RelativeLayout parentView;
    	
    	@Override
    	protected void onCreate(Bundle savedInstanceState) { 
    		super.onCreate(savedInstanceState);
    		setContentView(R.layout.activity_main);
    		
    		iv_main = (ImageView) findViewById(R.id.iv_main);
    		
    		parentView = (RelativeLayout) iv_main.getParent();
    		/* int right = parentView.getRight(); //0 int bottom = parentView.getBottom(); //0 Toast.makeText(this, right+"---"+bottom, 1).show(); */
    		//设置touch监听 
    		iv_main.setOnTouchListener(this);
    	}
    	
    	private int lastX;
    	private int lastY;
    	private int maxRight;
    	private int maxBottom;
    	
    	@Override
    	public boolean onTouch(View v, MotionEvent event) { 
    		//得到事件的坐标
    		int eventX = (int) event.getRawX();
    		int eventY = (int) event.getRawY();
    		switch (event.getAction()) { 
    		case MotionEvent.ACTION_DOWN:
    			
    			//得到父视图的right/bottom
    			if(maxRight==0) { //保证只赋一次值
    				maxRight = parentView.getRight();
    				maxBottom = parentView.getBottom();
    			}
    			
    			
    			//第一次记录lastX/lastY
    			lastX =eventX;
    			lastY = eventY;
    			break;
    		case MotionEvent.ACTION_MOVE:
    			//计算事件的偏移
    			int dx = eventX-lastX;
    			int dy = eventY-lastY;
    			//根据事件的偏移来移动imageView
    			int left = iv_main.getLeft()+dx;
    			int top = iv_main.getTop()+dy;
    			int right = iv_main.getRight()+dx;
    			int bottom = iv_main.getBottom()+dy;
    			
    			//限制left >=0
    			if(left<0) { 
    				right += -left;
    				left = 0;
    			}
    			//限制top
    			if(top<0) { 
    				bottom += -top;
    				top = 0;
    			}
    			//限制right <=maxRight
    			if(right>maxRight) { 
    				left -= right-maxRight;
    				right = maxRight;
    			}
    			//限制bottom <=maxBottom
    			if(bottom>maxBottom) { 
    				top -= bottom-maxBottom;
    				bottom = maxBottom;
    			}
    			
    			iv_main.layout(left, top, right, bottom);
    			//再次记录lastX/lastY
    			lastX = eventX;
    			lastY = eventY;
    			break;
    
    		default:
    			break;
    		}
    		return true;//所有的motionEvent都交给imageView处理
    	}
    }

原理，在触摸down的时候，记录lastX和lastY，在每一次move的时候计算偏移量，根据获取父view的右边和下边位置作为最大值，最终调用view的layout方法更新布局定位。在onTouch事件中，return true表示所有motiionEvent都交给imageView处理。

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