現在的智能手機不敢說百分百的都是觸摸屏,也應該是百分之九九以上爲觸摸屏了,觸摸屏爲我們操作無鍵盤、無鼠標的手機系統帶來了很多的便利。當用戶觸摸屏幕時會產生很多的觸摸事件,down、up、move等等。View類有個View.OnTouchListener內部接口,通過重寫他的onTouch(View v, MotionEvent event)方法,我們可以處理一些touch事件,如下:
public class MainActivity extends Activity {
...
// This example shows an Activity, but you would use the same approach if
// you were subclassing a View.
@Override
public boolean onTouchEvent(MotionEvent event){
int action = MotionEventCompat.getActionMasked(event);
switch(action) {
case (MotionEvent.ACTION_DOWN) :
Log.d(DEBUG_TAG,"Action was DOWN");
return true;
case (MotionEvent.ACTION_MOVE) :
Log.d(DEBUG_TAG,"Action was MOVE");
return true;
case (MotionEvent.ACTION_UP) :
Log.d(DEBUG_TAG,"Action was UP");
return true;
case (MotionEvent.ACTION_CANCEL) :
Log.d(DEBUG_TAG,"Action was CANCEL");
return true;
case (MotionEvent.ACTION_OUTSIDE) :
Log.d(DEBUG_TAG,"Movement occurred outside bounds " +
"of current screen element");
return true;
default :
return super.onTouchEvent(event);
}
}
OnTouch提供的事件還是相對較簡單,如果需要處理一些複雜的手勢,用這個接口就會很麻煩,因爲我們要根據用戶觸摸的軌跡去判斷是什麼手勢。Android sdk給我們提供了GestureDetector(Gesture:手勢Detector:識別)類,通過這個類我們可以識別很多的手勢。
public class GestureDetector extends Object
java.lang.Object
android.view.GestureDetector
GestureDetector屬於android.view包,android還提供了android.gesture包支持更多的手勢操作,以後我們會介紹到。官方的介紹中使用了GestureDetectorCompat處理手勢識別,爲什麼使用GestureDetectorCompat替換了GestureDetector呢,官方的是這樣解釋的:
GestureDetectorCompat實例化有下面兩種方法:
GestureDetector類對外提供了兩個接口:OnGestureListener,OnDoubleTapListener,還有一個內部類SimpleOnGestureListener;SimpleOnGestureListener類是GestureDetector提供給我們的一個更方便的響應不同手勢的類,它實現了上述兩個接口,該類是static class,也就是說它實際上是一個外部類,我們可以在外部繼承這個類,重寫裏面的手勢處理方法。因此實現手勢識別有兩種方法,一種實現OnGestureListener接口,另一種是使用SimpleOnGestureListener類。
OnGestureListener有下面的幾個動作:
按下(onDown): 剛剛手指接觸到觸摸屏的那一剎那,就是觸的那一下。
拋擲(onFling): 手指在觸摸屏上迅速移動,並鬆開的動作。
長按(onLongPress): 手指按在持續一段時間,並且沒有鬆開。
滾動(onScroll): 手指在觸摸屏上滑動。
按住(onShowPress): 手指按在觸摸屏上,它的時間範圍在按下起效,在長按之前。
擡起(onSingleTapUp):手指離開觸摸屏的那一剎那。
使用OnGestureListener接口,這樣需要重載OnGestureListener接口所有的方法,適合監聽所有的手勢,正如官方文檔提到的“Detecing All Supported Gestures”。
public class MainActivity extends Activity implements
GestureDetector.OnGestureListener,
GestureDetector.OnDoubleTapListener{
private static final String DEBUG_TAG = "Gestures";
private GestureDetectorCompat mDetector;
// Called when the activity is first created.
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Instantiate the gesture detector with the
// application context and an implementation of
// GestureDetector.OnGestureListener
mDetector = new GestureDetectorCompat(this,this);
// Set the gesture detector as the double tap
// listener.
mDetector.setOnDoubleTapListener(this);
}
@Override
public boolean onTouchEvent(MotionEvent event){
this.mDetector.onTouchEvent(event);
// Be sure to call the superclass implementation
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;
}
}
這樣會造成有些手勢動作我們用不到,但是還要重載。SimpleOnGestureListener類的出現爲我們解決了這個問題,如果你想“Detecting a Subset of Supported Gestures”,SimpleOnGestureListener是最好的選擇。
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;
}
}
}
最後了我們也解釋兩個問題:
1、onTouchEvent中爲什麼使用了MotionEventCompat,而不直接使用MotionEvent。因爲MotionEventCompat使更多的Action適配到API 4。
2、Android的view怎麼使用手勢,方法如下:
View myView = findViewById(R.id.my_view);
myView.setOnTouchListener(new OnTouchListener() {
public boolean onTouch(View v, MotionEvent event) {
// ... Respond to touch events
this.mDetector.onTouchEvent(event);
return super.onTouchEvent(event);
}
});
參考:
http://developer.android.com/reference/android/view/GestureDetector.html
http://developer.android.com/training/gestures/detector.html