定义View元素和他们的属性

Android上的布局就只有两种，一种是View和另外一种ViewGroup

ViewGroup就是前面文章中将到的三种Layout，决定了View的位置。

另外六种常见的View有

• TextView displays a formatted text label
• ImageView displays an image resource
• Button can be clicked to perform an action
• ImageButton displays a clickable image
• EditText is an editable text field for user input
• ListView is a scrollable list of items containing other views

View Identifiers

id

View Height and Width

<TextView
  android:layout_width="165dp" 
  android:layout_height="wrap_content" />

运行的时候改变view的属性

This can take the form of wrap_content (adjust height and width to the content size), match_parent (adjust height and width to the full size of the parent container), and a dimensions value such as 120dp. This can be changed at runtime in a number of ways:

// Change the width or height
int newInPixels = 50;
view.setLayoutParams(new LayoutParams(newInPixels, newInPixels));
// Trigger invalidation of the view to force adjustment
view.requestLayout();

Or we can change just the width or height individually:

int newDimensionInPixels = 50;
view.getLayoutParams().width = newDimensionInPixels;
view.getLayoutParams().height = newDimensionInPixels;
// Trigger invalidation of the view to force adjustment
view.requestLayout();

We can also set these dimensions in dp rather than pixels with:

int newDimensionInPixels = 50;
// convert to 50dp
int dimensionInDp = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, newDimensionInPixels, 
    getResources().getDisplayMetrics());
view.getLayoutParams().width = newDimensionInPixels;
view.getLayoutParams().height = dimensionInDp;
// Trigger invalidation of the view to force adjustment
view.requestLayout();

• Layout Margin defines the amount of space around the outside of a view
• Padding defines the amount of space around the contents or children of a view.

• gravity determines the direction that the contents of a view will align (like CSS text-align).
• layout_gravity determines the direction of the view within it's parent (like CSS float).

其它属性

Attribute	Description	Example Value
android:background	Background for the view	#ffffff
android:onClick	Method to invoke when clicked	onButtonClicked
android:visibility	Controls how view appears	invisible
android:hint	Hint text to display when empty	@string/hint
android:text	Text to display in view	@string/foo
android:textColor	Color of the text	#000000
android:textSize	Size of the text	21sp
android:textStyle	Style of the text formatting	bold