Android中實現Bitmap在自定義View中的放大與拖動

一基本實現思路：

基於View類實現自定義View –MyImageView類。在使用View的Activity類中完成OnTouchListener接口，實現對MotionEvent事件的監聽與處理，常見的MotionEvent事件如下：

ACTION_DOWN事件，記錄平移開始點
ACTION_UP事件，結束平移事件處理
ACTION_MOVE事件，記錄平移點，計算與開始點距離，實現Bitmap平移，在多點觸控時候，計算兩點之間的距離，實現圖像放大
ACTION_POINTER_DOWN事件，計算兩點之間的距離，作為初始距離，實現圖像手勢放大時候使用。
ACTION_POINTER_UP事件，結束兩點觸控放大圖像處理

放大與拖動
基於單點觸控實現Bitmap對象在View上的拖動、並且檢測View的邊緣，防止拖動過界。基於兩個點觸控實現Bitmap對象在View上的放大、並且檢測放大倍數。基於Matrix對象實現對Bitmap在View上放大與平移變換，Matrix對象是android中實現圖像幾何變換的矩陣，支持平移、放大、縮小、錯切、旋轉等常見操作。

Bitmap對象在View中的更新與顯示
通過重載onDraw方法，使用canvas實現繪制Bitmap對象、通過view.invalidate()方法實現View的刷新。

MyImageView類的重要方法說明：
initParameters()初始化所有需要用到的參數
setStartPoint()設置圖像平移的開始點坐標

setMovePoint()設置圖像平移的移動點坐標，然後集合開始點位置，計算它們之間的距離，從而得到Bitmap對象需要平移的兩個參數值sx、sy。其中還包括保證圖像不會越過View邊界的檢查代碼。

savePreviousResult()保存當前的平移數據，下次可以繼續在次基礎上平移Bitmap對象。

zoomIn()根據兩個點之間的歐幾裡德距離，通過初始距離比較，得到放大比例，實現Bitmap在View對象上的放大

 

Matrix中關於放大與平移的API

Matrix.postScale方法與Matrix.postTranslate方法可以不改變Bitmap對象本身實現平移與放大。

 

二：代碼實現

自定義View類使用xml布局如下：

 

自定義View實現代碼如下：

 

 

package com.example.matrixdemo;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Point;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.View;

public class MyImageView extends View {
	private Paint mPaint;
	private Bitmap bitmap;
	private Matrix matrix;
	
	// 平移開始點與移動點
	private Point startPoint;
	private Point movePoint;
	private float initDistance;

	// 記錄當前平移距離
	private int sx;
	private int sy;
	
	// 保存平移狀態
	private int oldsx;
	private int oldsy;
	
	// scale rate
	private float widthRate;
	private float heightRate;
	
	public MyImageView(Context context) {
		super(context);
	}
	
	public MyImageView(Context context, AttributeSet attrs) {
		super(context, attrs);
	}
	
	public void setBitmap(Bitmap bitmap) {
		this.bitmap = bitmap;
	}
	
	private void initParameters() {
		// 初始化畫筆
		mPaint = new Paint();
		mPaint.setColor(Color.BLACK);
		matrix = new Matrix();
		if(bitmap != null)
		{
			float iw = bitmap.getWidth();
			float ih = bitmap.getHeight();
			float width = this.getWidth();
			float height = this.getHeight();
			// 初始放縮比率
			widthRate = width / iw;
			heightRate = height / ih;
		}
		
		sx = 0;
		sy = 0;
		
		oldsx = 0;
		oldsy = 0;
		
	}
	
	public void setStartPoint(Point startPoint) {
		this.startPoint = startPoint;
	}
	
	public void setInitDistance(float initDistance) {
		this.initDistance = initDistance;
	}
	
	public void zoomIn(float distance)
	{
		float rate = distance / this.initDistance;
		float iw = bitmap.getWidth();
		float ih = bitmap.getHeight();
		float width = this.getWidth();
		float height = this.getHeight();
		// get scale rate
		widthRate = (width / iw ) * rate;
		heightRate = (height / ih) * rate;
		
		// make it same as view size
		float iwr = (width / iw );
		float ihr = (height / ih);
		if(iwr >= widthRate)
		{
			widthRate = (width / iw );
		}
		if(ihr >= heightRate)
		{
			heightRate = (height / ih);
		}
		
		// go to center
		oldsx = (int)((width - widthRate * iw) / 2);
		oldsy = (int)((height - heightRate * ih) / 2);
	}

	public void setMovePoint(Point movePoint) {
		this.movePoint = movePoint;
		sx = this.movePoint.x - this.startPoint.x;
		sy = this.movePoint.y - this.startPoint.y;
		
		float iw = bitmap.getWidth();
		float ih = bitmap.getHeight();
		
		// 檢測邊緣
		int deltax = (int)((widthRate * iw) - this.getWidth());
		int deltay = (int)((heightRate * ih) - this.getHeight());
		if((sx + this.oldsx) >= 0)
		{
			this.oldsx = 0;
			sx = 0;
		}
		else if((sx + this.oldsx) <= -deltax)
		{
			this.oldsx = -deltax;
			sx = 0;
		}
		
		if((sy + this.oldsy) >= 0)
		{
			this.oldsy = 0;
			this.sy = 0;
		}
		else if((sy + this.oldsy) <= -deltay)
		{
			this.oldsy = -deltay;
			this.sy = 0;
		}
		
		float width = this.getWidth();
		
		// 初始放縮比率
		float iwr = width / iw;
		if(iwr == widthRate)
		{
			sx = 0;
			sy = 0;
			oldsx = 0;
			oldsy = 0;
		}
	}
	
	public void savePreviousResult()
	{
		this.oldsx = this.sx + this.oldsx;
		this.oldsy = this.sy + this.oldsy;
		
		// zero
		sx = 0;
		sy = 0;
	}

	@Override
	protected void onDraw(Canvas canvas) {
		if(matrix == null)
		{
			initParameters();
		}
		if(bitmap != null)
		{
			matrix.reset();
			matrix.postScale(widthRate, heightRate);
			matrix.postTranslate(oldsx+sx, oldsy + sy);
			canvas.drawBitmap(bitmap, matrix, mPaint);
		}
		else
		{
			// fill rect
			Rect rect = new Rect(0, 0, getWidth(), getHeight());
			mPaint.setAntiAlias(true);
			mPaint.setColor(Color.BLACK);
			mPaint.setStyle(Style.FILL_AND_STROKE);
			canvas.drawRect(rect, mPaint);
		}
	}
}

Activity類中實現對View的OnTouchListener監聽與MotionEvent事件處理的代碼如下：

 

 

package com.example.matrixdemo;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Point;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;

public class MainActivity extends Activity implements OnTouchListener {

	public static final int SCALE_MODE = 4;
	public static final int TRANSLATION_MODE = 2;
	public static final int NULL_MODE = 1;
	private MyImageView myView;
	private int mode;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		startMyImageView();
	}

	private void startMyImageView() {
		myView = (MyImageView) this.findViewById(R.id.myView);
		Bitmap bitmap = BitmapFactory.decodeResource(this.getResources(),
				R.drawable.flower_001);
		myView.setBitmap(bitmap);
		myView.setOnTouchListener(this);
		myView.invalidate();
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onTouch(View view, MotionEvent event) {
		Log.i(touch event,touch x =  + event.getX());
		switch (MotionEvent.ACTION_MASK & event.getAction()) 
		{
			case MotionEvent.ACTION_DOWN:
				mode = TRANSLATION_MODE;
				myView.setStartPoint(new Point((int)event.getX(), (int)event.getY()));
				break;
			case MotionEvent.ACTION_POINTER_UP:
			case MotionEvent.ACTION_OUTSIDE:
			case MotionEvent.ACTION_UP:
				mode = NULL_MODE;
				myView.savePreviousResult();
				break;
			case MotionEvent.ACTION_POINTER_DOWN:
				mode = SCALE_MODE;
				myView.setInitDistance(calculateDistance(event));
				break;
			case MotionEvent.ACTION_MOVE:
				if(mode == SCALE_MODE)
				{
					float dis = calculateDistance(event);
					myView.zoomIn(dis);
				}
				else if(mode == TRANSLATION_MODE)
				{
					myView.setMovePoint(new Point((int)event.getX(), (int)event.getY()));
				}
				else
				{
					Log.i(unknow mode tag,do nothing......);
				}
				break;
		}
		myView.invalidate();
		return true;
	}

	private float calculateDistance(MotionEvent event) {
		float dx = event.getX(0) - event.getX(1);
		float dy = event.getY(0)  - event.getY(1);
		float distance = (float)Math.sqrt(dx*dx + dy*dy);
		return distance;
	}

}

三：運行效果如下