View基础知识
1、什么是View
View是Android中所有控件的基类，还有ViewGroup，翻译是控件组，ViewGroup也是继承了View，所以其实ViewGroup本身是一个控件只是其内部可能包含了许多控件。
2、View的位置参数
- top 左上角的纵坐标
- left 左上角的横坐标
- bottom 右下角的纵坐标
- right 右下角的横坐标
需要注意的是这些参数都是基于父容器来说的，并不是屏幕。
这是布局xml:
<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.example.administrator.test.MainActivity"> <RelativeLayout android:id="@+id/main_Relative1" android:layout_width="250dp" android:layout_height="250dp" android:layout_marginTop="50dp" android:layout_marginLeft="50dp" android:background="@color/colorPrimary"> <RelativeLayout android:id="@+id/main_Relative2" android:layout_width="100dp" android:layout_height="100dp" android:layout_marginTop="50dp" android:layout_marginLeft="50dp" android:background="@color/colorAccent"> </RelativeLayout> </RelativeLayout> <Button android:id="@+id/main_button1" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true"/> </RelativeLayout>
然后是Activity的Java代码：
public class MainActivity extends AppCompatActivity { private final static String TAG = "MainActivity"; private RelativeLayout relativeLayout1; private RelativeLayout relativeLayout2; private Button button1; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); relativeLayout1 = (RelativeLayout) findViewById(R.id.main_Relative1); relativeLayout2 = (RelativeLayout) findViewById(R.id.main_Relative1); button1 = (Button) findViewById(R.id.main_button1); button1.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { Log.d(TAG,"relativeLayout1_TOP = " + relativeLayout1.getTop()); Log.d(TAG,"relativeLayout1_Left = " + relativeLayout1.getLeft()); Log.d(TAG,"relativeLayout1_Bottom = " + relativeLayout1.getBottom()); Log.d(TAG,"relativeLayout1_Right = " + relativeLayout1.getRight()); Log.d(TAG,"relativeLayout2_TOP = " + relativeLayout2.getTop()); Log.d(TAG,"relativeLayout2_Left = " + relativeLayout2.getLeft()); Log.d(TAG,"relativeLayout2_Bottom = " + relativeLayout2.getBottom()); Log.d(TAG,"relativeLayout2_Right = " + relativeLayout2.getRight()); } }); } }
这里要注意的是不能直接在onCreate中使用getLeft, getRight, getTop, getBottom，这样直接使用返回的结果将是0，因为View的绘制晚于Activity的创建。
然后还要注意dp和像素的区别。不同的手机不一样。
输出：
12-19 10:40:27.594 22464-22464/com.example.administrator.test D/MainActivity: relativeLayout1_TOP = 150 12-19 10:40:27.594 22464-22464/com.example.administrator.test D/MainActivity: relativeLayout1_Left = 150 12-19 10:40:27.594 22464-22464/com.example.administrator.test D/MainActivity: relativeLayout1_Bottom = 900 12-19 10:40:27.595 22464-22464/com.example.administrator.test D/MainActivity: relativeLayout1_Right = 900 12-19 10:40:27.595 22464-22464/com.example.administrator.test D/MainActivity: relativeLayout2_TOP = 150 12-19 10:40:27.595 22464-22464/com.example.administrator.test D/MainActivity: relativeLayout2_Left = 150 12-19 10:40:27.595 22464-22464/com.example.administrator.test D/MainActivity: relativeLayout2_Bottom = 900 12-19 10:40:27.595 22464-22464/com.example.administrator.test D/MainActivity: relativeLayout2_Right = 900
从Android3.0开始，View在平移的过程中，top和left表示的是原始左上角的位置信息，其值不会发生改变。在平移过程中发生改变的x,y,translationX,translationY，x,y是View左上角的坐标，translationX,translationY是平移的距离。
x = left + translationX
y = top + translationY
3、View的滑动
首先是自定义控件的Java代码：
public class ima extends AppCompatImageView { private final static String TAG = "ima"; Scroller mScroller = new Scroller(getContext()); public ima(Context context) { super(context); } public ima(Context context, AttributeSet attrs) { super(context, attrs); } public ima(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); } //缓慢滚动到指定位置 public void smoothScrollTo(int destX, int destY){ int scrollX = getScrollX(); int scrollY = getScrollY(); Log.d(TAG,"scrollX = " + scrollX); Log.d(TAG,"scrollY = " + scrollY); int deltaX = scrollX - destX; int deltaY = scrollY - destY; //1000ms弹性滑动，效果就慢慢滑动 mScroller.startScroll(scrollX,scrollY,deltaX,deltaY,1000); invalidate(); } @Override public void computeScroll() { if(mScroller.computeScrollOffset()){ scrollTo(mScroller.getCurrX(),mScroller.getCurrY()); postInvalidate(); } } }
然后是Activity的Java代码
public class MainActivity extends AppCompatActivity { private final static String TAG = "MainActivity"; private ima ima; private Button button; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); button = (Button) findViewById(R.id.main_button1); ima = (ima) findViewById(R.id.main_ima1); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { ima.smoothScrollTo(60,60); Log.d(TAG,"ima_top = " + ima.getTop()); Log.d(TAG,"ima_left = " + ima.getLeft()); Log.d(TAG,"ima_ScaleX = " + ima.getScaleX()); Log.d(TAG,"ima_ScaleY = " + ima.getScaleY()); Log.d(TAG,"textView_x = " + ima.getX()); Log.d(TAG,"textView_y = " + ima.getY()); Log.d(TAG,"textView_getTranslationX = " + ima.getTranslationX()); Log.d(TAG,"textView_getTranslationY = " + ima.getTranslationY()); } }); } }
这是自定义的一个ima控件继承自AppCompatImageView。其中构造函数是直接继承来的。这里使用了Scroller实现View的弹性滑动。
Scroller mScroller = new Scroller(getContext());
首先使用Context创建一个Scroller对象。
//缓慢滚动到指定位置 public void smoothScrollTo(int destX, int destY){ int scrollX = getScrollX(); int scrollY = getScrollY();
Log.d(TAG,"scrollX = " + scrollX); Log.d(TAG,"scrollY = " + scrollY);
int deltaX = scrollX - destX; int deltaY = scrollY - destY; //1000ms弹性滑动，效果就慢慢滑动 mScroller.startScroll(scrollX,scrollY,deltaX,deltaY,1000); invalidate(); } @Override public void computeScroll() { if(mScroller.computeScrollOffset()){ scrollTo(mScroller.getCurrX(),mScroller.getCurrY()); postInvalidate(); } }
这里输入的参数为destX、destY为滑动的终点。调用的getScrollX()方法获得的是View的左边缘和View内容左边缘的距离，getScrollY()方法获得的是View的上边缘和View内容上边缘的距离。
