Android如何創建可拖動的圖片控件

2019-10-22 18:13:38

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來源：轉載

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本文實例為大家分享了Android創建可拖動圖片控件的具體代碼，供大家參考，具體內容如下

重載、自繪

1、從View派生一個控件類，構造函數中調用父類構造器。

2、重載其onDraw函數，在里面繪制圖片。（和windows的MFC有種似曾相識的感覺，可能安卓借鑒了windows的模式吧）

消息處理

拖動圖片的消息，主要是處理按下和移動兩個消息，重載onTouchEvent。數學知識（平移）：在ACTION_DOWN時記錄下坐標點，在ACTION_MOVE時根據當前位置與按下時的位置算出平移量。刷新控件，導致控件重繪，重繪時移動繪制的左上角坐標即可。

剛開始時，只是收到了ACTION_DOWN消息，ACTION_MOVE消息就是捕捉不到，上網搜了下，原來是我在onTouchEvent最后調用了父類函數return super.onTouchEvent(event);父類里面返回false表示對這些消息不予關注，后續的ACTION_MOVE和ACTION_UP就不會進來了。

代碼和配置

activity的XML配置

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"   android:layout_width="fill_parent"   android:layout_height="fill_parent"   android:orientation="vertical" >   <com.example.timertest.DragImageView      android:id="@+id/div"     android:layout_width="fill_parent"     android:layout_height="fill_parent"   /> </LinearLayout>

控件的自繪代碼

package com.example.timertest;   import java.util.ArrayList; import android.annotation.SuppressLint; import android.content.Context; import android.graphics.Bitmap; import android.graphics.Canvas; import android.graphics.Paint; import android.graphics.PointF; import android.graphics.Rect; import android.graphics.RectF; import android.util.AttributeSet; import android.view.MotionEvent; import android.view.View; import android.view.WindowManager;  @SuppressLint("ClickableViewAccessibility") public class DragImageView extends View{      private Bitmap bmp = null;   private PointF orgPos = new PointF(0, 0);   private PointF downPos = new PointF(0, 0);   private PointF movePos = new PointF(0, 0);   private boolean bMove = false;   private int nDstWidth = 0;   private int nDstHeight = 0;   private Rect rcSrc = new Rect(0, 0 , 0, 0);   private RectF rcDst = new RectF(0, 0, 0, 0);   private Paint paint = null;   public DragImageView(Context context) {     super(context);     // TODO Auto-generated constructor stub     paint = new Paint(Paint.ANTI_ALIAS_FLAG);     //setOnClickListener(new DivOnClickListener());     //setOnTouchListener(l);   }      public DragImageView(Context context, AttributeSet attrs) {     super(context, attrs);     //bmp = img;     paint = new Paint(Paint.ANTI_ALIAS_FLAG);   }   public DragImageView(Context context, AttributeSet attrs, int defStyleAttr){     super(context, attrs, defStyleAttr);     paint = new Paint(Paint.ANTI_ALIAS_FLAG);   }      public void SetImage(Bitmap img){     if ( bmp != null ){       bmp = null;     }     bmp = img;   }    @Override   public void addTouchables(ArrayList<View> views) {     // TODO Auto-generated method stub     super.addTouchables(views);   }    @Override   public boolean onTouchEvent(MotionEvent event) {     // TODO Auto-generated method stub     float fPosX = event.getX();     float fPosY = event.getY();     int nAct = event.getAction();     switch ( nAct ){     case MotionEvent.ACTION_MOVE:{       if ( !bMove )         bMove = true;       movePos.x = fPosX - downPos.x;       movePos.y = fPosY - downPos.y;       downPos.x = fPosX;       downPos.y = fPosY;       invalidate();     }       break;     case MotionEvent.ACTION_DOWN:{       downPos.x = fPosX;       downPos.y = fPosY;     }       break;     case MotionEvent.ACTION_UP:       break;     }     //一定要返回ture，如果返回父類方法即false，則后續的move up 消息都不會觸發。     return true;     //return super.onTouchEvent(event);   }    @Override   protected void onDraw(Canvas canvas) {     // TODO Auto-generated method stub     super.onDraw(canvas);     if ( bmp == null )       return ;     int nWidth = bmp.getWidth();     int nHeight = bmp.getHeight();     if ( !bMove ){       orgPos = GetCenterPos();     }     else{       orgPos.x += movePos.x;       orgPos.y += movePos.y;     }     rcSrc.right = nWidth;     rcSrc.bottom = nHeight;     rcDst.left = orgPos.x;     rcDst.top = orgPos.y;     rcDst.right = orgPos.x+nDstWidth;     rcDst.bottom = orgPos.y+nDstHeight;     canvas.drawBitmap(bmp, rcSrc, rcDst, paint);   }      protected PointF GetCenterPos(){     PointF pt = new PointF(0, 0);     if ( bmp == null )       return pt;     WindowManager wm = (WindowManager)getContext().getSystemService(Context.WINDOW_SERVICE);     //wm.getDefaultDisplay().getSize(pt);     int nScrWidth = wm.getDefaultDisplay().getWidth();     @SuppressWarnings("deprecation")     int nScrHeight = wm.getDefaultDisplay().getHeight();     int nWidth = bmp.getWidth();     int nHeight = bmp.getHeight();     float fImgRate = nWidth/(float)nHeight;     float fScrRate = nScrWidth/(float)nScrHeight;     if ( nWidth>nScrWidth && nHeight>nScrHeight ){       if ( fImgRate > fScrRate ){                  nDstWidth = nScrWidth;         nDstHeight = (int)(nScrWidth/fImgRate);        }       else{                  nDstHeight = nScrHeight;         nDstWidth= (int)(nScrHeight*fImgRate);          }     }     else if ( nWidth>nScrWidth ){       nDstWidth = nScrWidth;       nDstHeight = nHeight;     }     else if ( nHeight>nScrHeight ){       nDstWidth = nWidth;       nDstHeight = nScrHeight;     }     else{       nDstWidth = nWidth;       nDstHeight = nHeight;     }     pt.y = (nScrHeight-nDstHeight)/2.0f;     pt.x = (nScrWidth-nDstWidth)/2.0f;     return pt;   }     }

其中GetCenterPos函數是根據圖片尺寸計算適合屏幕居中的方法。

運行程序

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