Android開(kāi)發(fā)藝術(shù)探索筆記 ——View（一）

View的基礎(chǔ)知識(shí)

什么是View

View是Android中所有控件的基類。是一種界面層控件的抽象。

View的位置參數(shù)

Paste_Image.png

Paste_Image.png

MotionEvent

• ACTION_DOWN
• ACTION_MOVE
• ACTION_UP

MotionEvent獲取點(diǎn)擊事件x,y坐標(biāo):

getX/getY 相對(duì)于View左上角
getRawX/getRawY 相對(duì)于手機(jī)屏幕左上角

  //在View或Activity中攔截touch events顶瞒，重寫onTouchEvent方法
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = MotionEventCompat.getActionMasked(event);
        switch (action) {
            case (MotionEvent.ACTION_DOWN):
                Log.d(TAG,"action down");
                return true;
            case (MotionEvent.ACTION_MOVE):
                Log.d(TAG,"action move");
                return true;
            case (MotionEvent.ACTION_UP):
                Log.d(TAG,"action up");
                return true;
            case (MotionEvent.ACTION_CANCEL):
                Log.d(TAG,"action cancel");
                return true;
            case (MotionEvent.ACTION_OUTSIDE):
                Log.d(TAG,"action outside");
                return true;
            default:
                return super.onTouchEvent(event);
        }
    }
    //對(duì)于View，可以使用setOnTouchListener()方法來(lái)監(jiān)聽(tīng)touch events而不需要繼承現(xiàn)有的View
    View myView = findViewById(R.id.my_view);
myView.setOnTouchListener(new OnTouchListener() {
    public boolean onTouch(View v, MotionEvent event) {
        // ... Respond to touch events
        return true;
    }
});

TouchSlop

滑動(dòng)的最小距離，常量留搔，和設(shè)備有關(guān)。

//獲取方式:
ViewConfiguration.get(getContext()).getScaledTouchSlop();

VelocityTracker

學(xué)習(xí)資料：
1.https://developer.android.com/training/gestures/movement.html

追蹤手指滑動(dòng)的速度

使用過(guò)程:

  //在View的onTouchEvent方法中
  VelocityTracker velocityTracker = VelocityTracker.obtain();
  velocityTracker.addMoveMent(event);
  
  //時(shí)間間隔設(shè)為1000ms
  tracker.computeCurrentVelocity(1000);
  int Vx = (int)velocityTracker.getXVelocity();
  int Vy = (int)VelocityTracker.getYVelocity();
  
  //不再使用的時(shí)候铛铁，需要清除并回收
  velocityTracker.clear();
  velocityTracker.recycle();

GestureDetector

手勢(shì)監(jiān)測(cè):單擊隔显，滑動(dòng)，長(zhǎng)按饵逐，雙擊等等括眠。

使用方法:

• 1.實(shí)例化GestureDetectorCompat類
• 2.如需監(jiān)測(cè)所有的手勢(shì)，則實(shí)現(xiàn)GestureDetector.OnGestureListener接口和GestureDetector.OnDoubleTapListener接口倍权。
• 3.若只需監(jiān)測(cè)部分手勢(shì)掷豺，則繼承GestureDetector.SimpleOnGestureListener類。

//監(jiān)測(cè)所有的手勢(shì)
public class MainActivity extends Activity implements
        GestureDetector.OnGestureListener,
        GestureDetector.OnDoubleTapListener{

    private static final String DEBUG_TAG = "Gestures";
    private GestureDetectorCompat mDetector;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //實(shí)例化GestureDetectorCompat
        mDetector = new GestureDetectorCompat(this,this);
        //將雙擊事件交給GestureDetectorCompat監(jiān)聽(tīng)
        mDetector.setOnDoubleTapListener(this);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event){
        this.mDetector.onTouchEvent(event);
        return super.onTouchEvent(event);
    }

    @Override
    public boolean onDown(MotionEvent event) {
        Log.d(DEBUG_TAG,"onDown: " + event.toString());
        return true;
    }

    @Override
    public boolean onFling(MotionEvent event1, MotionEvent event2,
            float velocityX, float velocityY) {
        Log.d(DEBUG_TAG, "onFling: " + event1.toString()+event2.toString());
        return true;
    }

    @Override
    public void onLongPress(MotionEvent event) {
        Log.d(DEBUG_TAG, "onLongPress: " + event.toString());
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX,
            float distanceY) {
        Log.d(DEBUG_TAG, "onScroll: " + e1.toString()+e2.toString());
        return true;
    }

    @Override
    public void onShowPress(MotionEvent event) {
        Log.d(DEBUG_TAG, "onShowPress: " + event.toString());
    }

    @Override
    public boolean onSingleTapUp(MotionEvent event) {
        Log.d(DEBUG_TAG, "onSingleTapUp: " + event.toString());
        return true;
    }

    @Override
    public boolean onDoubleTap(MotionEvent event) {
        Log.d(DEBUG_TAG, "onDoubleTap: " + event.toString());
        return true;
    }

    @Override
    public boolean onDoubleTapEvent(MotionEvent event) {
        Log.d(DEBUG_TAG, "onDoubleTapEvent: " + event.toString());
        return true;
    }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent event) {
        Log.d(DEBUG_TAG, "onSingleTapConfirmed: " + event.toString());
        return true;
    }
}



//監(jiān)測(cè)部分手勢(shì)
public class MainActivity extends Activity {

    private GestureDetectorCompat mDetector;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mDetector = new GestureDetectorCompat(this, new MyGestureListener());
    }

    @Override
    public boolean onTouchEvent(MotionEvent event){
        this.mDetector.onTouchEvent(event);
        return super.onTouchEvent(event);
    }

    class MyGestureListener extends GestureDetector.SimpleOnGestureListener {
        private static final String DEBUG_TAG = "Gestures";

        @Override
        public boolean onDown(MotionEvent event) {
            Log.d(DEBUG_TAG,"onDown: " + event.toString());
            return true;
        }

        @Override
        public boolean onFling(MotionEvent event1, MotionEvent event2,
                float velocityX, float velocityY) {
            Log.d(DEBUG_TAG, "onFling: " + event1.toString()+event2.toString());
            return true;
        }
    }
}

Scroller

彈性滑動(dòng)對(duì)象薄声，用于實(shí)現(xiàn)View的彈性滑動(dòng)当船。

學(xué)習(xí)資料:
1.Android Scroller完全解析，關(guān)于Scroller你所需知道的一切
2.Animating a Scroll Gesture

Scroller的基本用法:

• 1.創(chuàng)建Scroller實(shí)例
• 2.調(diào)用startScroll()方法來(lái)初始化
• 3.重寫View的computeScroll()方法默辨，并在其內(nèi)部完成平滑移動(dòng)的邏輯德频。

View的滑動(dòng)

三種方式實(shí)現(xiàn)View的滑動(dòng):

• 1.View的ScrollTo和ScrollBy方法。
• 2.動(dòng)畫
• 3.改變View的LayoutParams使View重新布局從而實(shí)現(xiàn)滑動(dòng)

使用ScrollTo和ScrollBy

• ScrollTo相對(duì)于初始位置滾動(dòng)某段距離缩幸。
• ScrollBy相對(duì)于當(dāng)前位置滾動(dòng)某段距離壹置。
• 其中，水平方向表谊，正值為向左滾動(dòng)钞护，負(fù)值為向右滾動(dòng)。豎直方向铃肯，正值為向上滾動(dòng)患亿，負(fù)值為向下滾動(dòng)。
• 兩個(gè)Scroll方法的滾動(dòng)都是跳躍式的，沒(méi)有平滑移動(dòng)的效果步藕。

使用動(dòng)畫

使用動(dòng)畫操作View的translationX和translationY兩個(gè)屬性來(lái)移動(dòng)View惦界。可使用屬性動(dòng)畫/View動(dòng)畫咙冗。

View動(dòng)畫是對(duì)View的影像進(jìn)行操作的沾歪。也就是說(shuō)View動(dòng)畫并不能真正的改變View的位置。
屬性動(dòng)畫是真正改變View的位置雾消，但它是從Android3.0開(kāi)始推出的灾搏。

//View動(dòng)畫實(shí)現(xiàn)移動(dòng)
<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:fillAfter="true"
    >
   <translate
       android:fromXDelta="0"
       android:fromYDelta="0"
       android:toXDelta="500"
       android:toYDelta="1000"
       android:duration="10000"
       android:interpolator="@android:anim/linear_interpolator"
       />
</set>

 Animation animation = AnimationUtils.loadAnimation(this, R.anim.translate);
        layout.setAnimation(animation);
        animation.start();

//使用屬性動(dòng)畫實(shí)現(xiàn)移動(dòng)
ObjectAnimator.ofFloat(layout,"translationX",0,100).setDuration(1000).start();

改變布局參數(shù)

改變布局參數(shù)LayoutParams。

 ViewGroup.MarginLayoutParams params = (ViewGroup.MarginLayoutParams) layout.getLayoutParams();
                params.width+=1000;
                params.leftMargin+=1000;
                layout.requestLayout();

三種滑動(dòng)方式的對(duì)比

彈性滑動(dòng)

將一次時(shí)間長(zhǎng)的滑動(dòng)分成若干次短的滑動(dòng)桑腮。

使用Scroller

//1.創(chuàng)建Scroller
Scroller scroller = new Scroller(context);
...

//2.調(diào)用Scroller的startScroll方法
int scrollX = getScrollX();
int deltaX = destX - scrollX;
scroller.startScroll(scrollX,0,deltaX,0,1000);
invalidate();

//3.復(fù)寫computeScroll()方法
@Override
public void computeScroll(){
    if(scroller.computeScrollOffset()){
       scrollTo(scroller.getCurrX(),scroller.getCurrY());
       invalidate();
    }
}