1、最近打开的应用不在最近任务列表中显示

android:excludeFromRecents="true"

设置为true,则排除在最近任务列表之外，不在最近任务列表中显示

2、判断一个一个String str 是否为NULL或者是否为空字符串

TextUtils.isEmpty(str)

3、android:imeOptions="actionSearch|flagNoFullscreen"的用法

在做一个把EditText放到到ActionBar中作为搜索框的功能时，设置EditText的属性为android:imeOptions="actionSearch"，会遇到一个问题，当在横屏时，EditText的宽度会填充掉屏幕上除了软键盘之外的地方，与需求不符，改为android:imeOptions="actionSearch|flagNoFullscreen"后就OK了。

4、改变图片亮度的方法

1、使用image.setColorFilter(Color.GRAY,PorterDuff.Mode.MULTIPLY);可以使图片变暗，然后使用image.clearColorFilter();清除滤镜，恢复到原来的亮度；
2、使用
int brightness = -80;
ColorMatrix matrix = new ColorMatrix();
matrix.set(new float[] { 1, 0, 0, 0, brightness, 0, 1, 0, 0,
brightness, 0, 0, 1, 0, brightness, 0, 0, 0, 1, 0 });
v.setColorFilter(new ColorMatrixColorFilter(matrix));
但这种方法会使颜色不太正常，图片留有黑边；

5、用Handler来实现有时间间隔事件的判断

看到Android中GestureDetector.java是用下面代码实现手势的单击和双击判断的：

public boolean onTouchEvent(MotionEvent ev) {
…… case MotionEvent.ACTION_DOWN: if (mDoubleTapListener != null) {
boolean hadTapMessage = mHandler.hasMessages(TAP);
if (hadTapMessage) mHandler.removeMessages(TAP);
if ((mCurrentDownEvent != null) && (mPreviousUpEvent != null) && hadTapMessage && isConsideredDoubleTap(mCurrentDownEvent, mPreviousUpEvent, ev)) {
// This is a second tap mIsDoubleTapping = true;
// Give a callback with the first tap of the double-tap handled |= mDoubleTapListener.onDoubleTap(mCurrentDownEvent);
// Give a callback with down event of the double-tap handled |= mDoubleTapListener.onDoubleTapEvent(ev);
}
else {
// This is a first tap mHandler.sendEmptyMessageDelayed(TAP, DOUBLE_TAP_TIMEOUT);
}
}
……}
private boolean isConsideredDoubleTap(MotionEvent firstDown, MotionEvent firstUp, MotionEvent secondDown) {
if (!mAlwaysInBiggerTapRegion) {
return false;
}
final long deltaTime = secondDown.getEventTime() - firstUp.getEventTime();
if (deltaTime > DOUBLE_TAP_TIMEOUT || deltaTime < DOUBLE_TAP_MIN_TIME) {
return false;
}
int deltaX = (int) firstDown.getX() - (int) secondDown.getX();
int deltaY = (int) firstDown.getY() - (int) secondDown.getY();
return (deltaX * deltaX + deltaY * deltaY < mDoubleTapSlopSquare);
}
private class GestureHandler extends Handler {
GestureHandler() {
super();
}
GestureHandler(Handler handler) {
super(handler.getLooper());
}
@Override public void handleMessage(Message msg) {
switch (msg.what) {
case SHOW_PRESS: mListener.onShowPress(mCurrentDownEvent);
break;
case LONG_PRESS: dispatchLongPress();
break;
case TAP: // If the user'
s finger is still down, do not count it as a tap if (mDoubleTapListener != null) {
if (!mStillDown) {
mDoubleTapListener.onSingleTapConfirmed(mCurrentDownEvent);
}
else {
mDeferConfirmSingleTap = true;
}
}
break;
default: throw new RuntimeException("Unknown message " + msg);
//never }
}

具体可以参考源码，这里是妙用了mHandler.sendEmptyMessageDelayed，如果在DOUBLE_TAP_TIMEOUT时间内mHandler把TAP消息发送出去了，就是单击时间，如果在这个时间内没有发送出去，就是双击事件。