報(bào)出異常的原因是由于少添加了構(gòu)造方法，三個(gè)構(gòu)造方法需要寫完整，不能只寫一個(gè)。參數(shù)為(Context, AttributeSet)，其中第二個(gè)參數(shù)用來將xml文件中的屬性初始化。

自定義控件若需要在xml文件中使用，就必須重寫帶如上兩個(gè)參數(shù)的構(gòu)造方法。

package?sunny.example.layoutparamstaddrule;

import?android.content.Context;
import?android.util.AttributeSet;
import?android.widget.Button;
import?android.widget.RelativeLayout;
import?android.widget.RelativeLayout.LayoutParams;
import?android.widget.TextView;

public??class?TestView?extends?RelativeLayout{
	
	private?LayoutParams?mLayoutParams_1,mLayoutParams_2;
	Button?mButton;
	TextView?mTextView;
	public?TestView(Context?context)?{
		super(context);
		//?TODO?Auto-generated?constructor?stub
		mButton?=?new?Button(context);
		mTextView?=?new?TextView(context);
		init();
		
	}
	public?TestView(Context?context,?AttributeSet?attrs)?{
		super(context,?attrs);
		//?TODO?Auto-generated?constructor?stub
		mButton?=?new?Button(context);
		mTextView?=?new?TextView(context);
		init();
	}
	public?TestView(Context?context,?AttributeSet?attrs,?int?defStyle)?{
		super(context,?attrs,?defStyle);
		//?TODO?Auto-generated?constructor?stub
		mButton?=?new?Button(context);
		mTextView?=?new?TextView(context);
		init();
	}
	
	public?void?init(){
		
		mLayoutParams_1?=?new?LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.WRAP_CONTENT);
		mLayoutParams_1.addRule(RelativeLayout.ALIGN_TOP);
		addView(mButton,mLayoutParams_1);
		
		
		mLayoutParams_2?=?new?LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.WRAP_CONTENT);
		mLayoutParams_2.addRule(RelativeLayout.BELOW,?TRUE);
		mTextView.setText("Hey");
		addView(mTextView,mLayoutParams_2);
	}
}

自定義控件在XML文件中使用

LayoutPrams

RelativeLayout.LayoutParams extends ViewGroup.MarginLayoutParams
java.lang.Object ???? android.view.ViewGroup.LayoutParams ? ???? android.view.ViewGroup.MarginLayoutParams ? ? ???? android.widget.RelativeLayout.LayoutParamsRelativeLayout.LayoutParams(Context c, AttributeSet attrs) RelativeLayout.LayoutParams(int w, int h) RelativeLayout.LayoutParams(ViewGroup.LayoutParams source) RelativeLayout.LayoutParams(ViewGroup.MarginLayoutParams source) RelativeLayout.LayoutParams(RelativeLayout.LayoutParams source)Copy constructor.

RelativeLayout.LayoutParams的方法： public void addRule (int verb)

Adds a layout rule to be interpreted by the RelativeLayout. This method should only be used for constraints that don't refer to another sibling (e.g., CENTER_IN_PARENT) or take a boolean value (TRUE for true or 0 for false). To specify a verb that takes a subject, use addRule(int, int) instead.

ParametersOne of the verbs defined by RelativeLayout, such as ALIGN_WITH_PARENT_LEFT. public void addRule (int verb, int anchor)

Adds a layout rule to be interpreted by the RelativeLayout. Use this for verbs that take a target, such as a sibling (ALIGN_RIGHT) or a boolean value (VISIBLE).

ParametersOne of the verbs defined by RelativeLayout, such as ALIGN_WITH_PARENT_LEFT.The id of another view to use as an anchor, or a boolean value(represented asTRUE) for true or 0 for false). For verbs that don't refer to another sibling (for example, ALIGN_WITH_PARENT_BOTTOM) just use -1

RelativeLayout.LayoutParams.addRule() 方法，該方法有兩種重載方式：

addRule(int verb) ：用此方法時(shí)，所設(shè)置節(jié)點(diǎn)的屬性不能與其它兄弟節(jié)點(diǎn)相關(guān)聯(lián)或者屬性值為布爾值（布爾值的屬性，設(shè)置時(shí)表示該屬性為 true，不設(shè)置就默認(rèn)為 false），比如：addRule(RelativeLayout.CENTER_VERTICAL) 就表示在 RelativeLayout 中的相應(yīng)節(jié)點(diǎn)是垂直居中的。

addRule(int verb, int anchor) ：該方法所設(shè)置節(jié)點(diǎn)的屬性必須關(guān)聯(lián)其它的兄弟節(jié)點(diǎn)或者屬性為布爾值（ 屬性為布爾值時(shí)，anchor 為 RelativeLayout.TRUE 表示 true，anchor 為0表示 false），比如：addRule(RelativeLayout.ALIGN_LEFT, R.id.date) 就表示 RelativeLayout 中的相應(yīng)節(jié)點(diǎn)放置在一個(gè) id 值為 date 的兄弟節(jié)點(diǎn)的左邊。