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LayoutParams源码分析
概述
- LayoutParams是布局参数的意思,我们在XML布局文件里的layout_xxx等属性都是对LayoutParams的描述。
- LayoutParams不属于View,是ViewGroup控制View的具体显示在哪里。
LayoutParams基本用法
TextView textView1 = new TextView(this);
textView1.setText("TextView1");
linearLayout.addView(textView1);
TextView textView2 = new TextView(this);
textView2.setText("TextView2");
textView2.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT));
linearLayout.addView(textView2);
TextView textView3 = new TextView(this);
textView3.setText("TextView3");
textView3.setLayoutParams(new LinearLayout.LayoutParams(100, 100));
linearLayout.addView(textView3);
LayoutParams源码分析
ViewGroup.LayoutParams
public LayoutParams(Context c, AttributeSet attrs) {
TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.ViewGroup_Layout);
setBaseAttributes(a,
R.styleable.ViewGroup_Layout_layout_width,
R.styleable.ViewGroup_Layout_layout_height);
a.recycle();
}
public LayoutParams(int width, int height) {
this.width = width;
this.height = height;
}
public LayoutParams(LayoutParams source) {
this.width = source.width;
this.height = source.height;
}
LayoutParams() {
}
ViewGroup.MarginLayoutParams
public static class MarginLayoutParams extends ViewGroup.LayoutParams {
public int leftMargin;
public int topMargin;
public int rightMargin;
public int bottomMargin;
private int startMargin = DEFAULT_MARGIN_RELATIVE;
private int endMargin = DEFAULT_MARGIN_RELATIVE;
public static final int DEFAULT_MARGIN_RELATIVE = Integer.MIN_VALUE;
public MarginLayoutParams(Context c, AttributeSet attrs) {
super();
TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.ViewGroup_MarginLayout);
setBaseAttributes(a,
R.styleable.ViewGroup_MarginLayout_layout_width,
R.styleable.ViewGroup_MarginLayout_layout_height);
int margin = a.getDimensionPixelSize(
com.android.internal.R.styleable.ViewGroup_MarginLayout_layout_margin, -1);
if (margin >= 0) {
leftMargin = margin;
topMargin = margin;
rightMargin= margin;
bottomMargin = margin;
} else {
int horizontalMargin = a.getDimensionPixelSize(
R.styleable.ViewGroup_MarginLayout_layout_marginHorizontal, -1);
int verticalMargin = a.getDimensionPixelSize(
R.styleable.ViewGroup_MarginLayout_layout_marginVertical, -1);
...
}
...
}
}
addView流程
public void addView(View child) {
addView(child, -1);
}
public void addView(View child, int index) {
if (child == null) {
throw new IllegalArgumentException("Cannot add a null child view to a ViewGroup");
}
LayoutParams params = child.getLayoutParams();
//若子View的LayoutParams为null,则使用默认LayoutParams
if (params == null) {
params = generateDefaultLayoutParams();
if (params == null) {
throw new IllegalArgumentException(
"generateDefaultLayoutParams() cannot return null");
}
}
addView(child, index, params);
}
//生成默认LayoutParams
@Override
protected LayoutParams generateDefaultLayoutParams() {
if (mOrientation == HORIZONTAL) {
return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
} else if (mOrientation == VERTICAL) {
return new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
}
return null;
}
public void addView(View child, int index, LayoutParams params) {
if (DBG) {
System.out.println(this + " addView");
}
if (child == null) {
throw new IllegalArgumentException("Cannot add a null child view to a ViewGroup");
}
requestLayout();
invalidate(true);
addViewInner(child, index, params, false);
}
private void addViewInner(View child, int index, LayoutParams params,
boolean preventRequestLayout) {
...
//检查LayoutParams是否合法,若不合法则使用默认值
if (!checkLayoutParams(params)) {
params = generateLayoutParams(params);
}
...
//子View添加到mChildren数组
addInArray(child, index);
...
}
//检查LayoutParams是否合法
@Override
protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
return p instanceof LinearLayout.LayoutParams;
}
@Override
public LayoutParams generateLayoutParams(AttributeSet attrs) {
return new LinearLayout.LayoutParams(getContext(), attrs);
}
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