我正在尝试访问另一个xml文件中的按钮，该文件用于自定义列表中的每一行。但是我怎么能这样做，因为我在设置onClick监听器时得到一个nullpointer异常。我的代码如下所示。
main.xml中
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<ListView android:id="@+id/List"
android:layout_width="fill_parent"
android:layout_height="fill_parent"/>
</LinearLayout>
row.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/list_item">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:id="@+id/list_item_text_view"
android:textSize="20sp"
android:padding="10dp"
android:layout_weight="1"
android:layout_marginLeft="35dp" />
<Button
android:id="@+id/b1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
这是我的活动课
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button b1 = (Button)findViewById(R.id.b1);
b1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
所以基本上如何在main.xml上设置活动视图时将onclicklistener设置为row.xml的b1
答案 0 :(得分：3)
使用LayoutInflater：
public class Main extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
LayoutInflater inflater = this.getLayoutInflater();
LinearLayout v = (LinearLayout)inflater.inflate(R.layout.hello, null);
Button bt1 = (Button)v.findViewById(R.id.btLog);
bt1.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
}
}
更新 * 可扩展的布局 *
public class ExpandablePanel extends LinearLayout {
private final int mHandleId;
private final int mContentId;
private View mHandle;
private View mContent;
private boolean mExpanded = false;
private int mCollapsedHeight = 0;
private int mContentHeight = 0;
private int mAnimationDuration = 0;
private OnExpandListener mListener;
public ExpandablePanel(Context context) {
this(context, null);
}
public ExpandablePanel(Context context, AttributeSet attrs) {
super(context, attrs);
mListener = new DefaultOnExpandListener();
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.ExpandablePanel, 0, 0);
// How high the content should be in "collapsed" state
mCollapsedHeight = (int) a.getDimension(R.styleable.ExpandablePanel_collapsedHeight, 0.0f);
// How long the animation should take
mAnimationDuration = a.getInteger(R.styleable.ExpandablePanel_animationDuration, 500);
int handleId = a.getResourceId(R.styleable.ExpandablePanel_handle, 0);
if (handleId == 0) {
throw new IllegalArgumentException(
"The handle attribute is required and must refer "
+ "to a valid child.");
}
int contentId = a.getResourceId(R.styleable.ExpandablePanel_content, 0);
if (contentId == 0) {
throw new IllegalArgumentException("The content attribute is required and must refer to a valid child.");
}
mHandleId = handleId;
mContentId = contentId;
a.recycle();
}
public void setOnExpandListener(OnExpandListener listener) {
mListener = listener;
}
public void setCollapsedHeight( int collapsedHeight ) { mCollapsedHeight = collapsedHeight; android.view.ViewGroup.LayoutParams lp = mContent.getLayoutParams(); lp.height = mCollapsedHeight; mContent.setLayoutParams( lp ); }
public void setAnimationDuration(int animationDuration) {
mAnimationDuration = animationDuration;
}
@Override
protected void onFinishInflate() {
super.onFinishInflate();
mHandle = findViewById(mHandleId);
if (mHandle == null) {
throw new IllegalArgumentException(
"The handle attribute is must refer to an"
+ " existing child.");
}
mContent = findViewById(mContentId);
if (mContent == null) {
throw new IllegalArgumentException(
"The content attribute must refer to an"
+ " existing child.");
}
android.view.ViewGroup.LayoutParams lp = mContent.getLayoutParams();
lp.height = mCollapsedHeight;
mContent.setLayoutParams(lp);
mHandle.setOnClickListener(new PanelToggler());
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// First, measure how high content wants to be
mContent.measure(widthMeasureSpec, MeasureSpec.UNSPECIFIED);
mContentHeight = mContent.getMeasuredHeight();
if (mContentHeight < mCollapsedHeight) {
mHandle.setVisibility(View.GONE);
} else {
mHandle.setVisibility(View.VISIBLE);
}
// Then let the usual thing happen
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
private class PanelToggler implements OnClickListener {
public void onClick(View v) {
Animation a;
if (mExpanded) {
a = new ExpandAnimation(mContentHeight, mCollapsedHeight);
mListener.onCollapse(mHandle, mContent);
} else {
a = new ExpandAnimation(mCollapsedHeight, mContentHeight);
mListener.onExpand(mHandle, mContent);
}
a.setDuration(mAnimationDuration);
if(mContent.getLayoutParams().height == 0) //Need to do this or else the animation will not play if the height is 0
{
android.view.ViewGroup.LayoutParams lp = mContent.getLayoutParams();
lp.height = 1;
mContent.setLayoutParams(lp);
mContent.requestLayout();
}
mContent.startAnimation(a);
mExpanded = !mExpanded;
}
}
private class ExpandAnimation extends Animation {
private final int mStartHeight;
private final int mDeltaHeight;
public ExpandAnimation(int startHeight, int endHeight) {
mStartHeight = startHeight;
mDeltaHeight = endHeight - startHeight;
}
@Override
protected void applyTransformation(float interpolatedTime, Transformation t) {
android.view.ViewGroup.LayoutParams lp = mContent.getLayoutParams();
lp.height = (int) (mStartHeight + mDeltaHeight * interpolatedTime);
mContent.setLayoutParams(lp);
}
@Override
public boolean willChangeBounds() {
return true;
}
}
public interface OnExpandListener {
public void onExpand(View handle, View content);
public void onCollapse(View handle, View content);
}
private class DefaultOnExpandListener implements OnExpandListener {
public void onCollapse(View handle, View content) {}
public void onExpand(View handle, View content) {}
}
}
<强>布局： 把它放在首位：xmlns：cl =“http://schemas.android.com/res/com.example.androidapp.widgets” Eclipse将始终在此布局中指示错误，因为ExpandablePanel.class中的Throw Exceptions，因此您可以隐藏这些行以查看可扩展布局的显示方式并设置其按钮和文本子项。
<com.example.androidapp.widgets.ExpandablePanel
android:id="@+id/theId"
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:orientation="vertical"
app:collapsedHeight="80dp"
app:content="@+id/value"
app:handle="@+id/expand"
cl:collapsedHeight="50dip"
cl:content="@+id/value"
cl:handle="@+id/expand" >
<TextView
android:id="@id/value"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="hejahdkashfa afsjkhas lf ksajfh as fkjsah asf kfsahkjfas klfajsh flkas klfajsh lasfkl aklfsjh klsa ffhaskljfha dfasfa s safjsfkhasjkf fjakshfjkasf jksfhjkasf sjakfhas kjfa sjkfhakjsfh asjsfhkjashf askjsf sakjfh as fadsfasf af asf asf" />
<Button
android:id="@id/expand"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical|center_horizontal"
android:text="More" />
</com.example.androidapp.widgets.ExpandablePanel>
如何设置展开式面板：
// Set expandable panel listener
ExpandablePanel panel = (ExpandablePanel)findViewById(R.id.theId);
panel.setCollapsedHeight(50);
panel.setContentDescription(descricao);
panel.setOnExpandListener(new ExpandablePanel.OnExpandListener() {
public void onCollapse(View handle, View content) {
Button btn = (Button)handle;
btn.setText("More");
}
public void onExpand(View handle, View content) {
Button btn = (Button)handle;
btn.setText("Less");
}
});
答案 1 :(得分：1)
你不是从那里来的。该辅助xml文件未膨胀或设置为上下文视图，因此该按钮不存在。
您可以做的是在getView函数的列表适配器中，您将为该行视图充气（对于不同的行可能会多次）。一旦你给它充气，你将获得行xml中顶级视图的View类，然后就可以在那里运行findViewByID。