Java Android onclickEventListener异常
我有以下代码Java Android onclickEventListener异常,java,android,Java,Android,我有以下代码 public class StartingPoint extends ActionBarActivity { int counter; Button add, substract; TextView display; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.a
public class StartingPoint extends ActionBarActivity {
int counter;
Button add, substract;
TextView display;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_starting_point);
counter = 0;
add = (Button) findViewById(R.id.btn_add);
substract = (Button) findViewById(R.id.btn_subscract);
display = (TextView) findViewById(R.id.txt_display);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
counter++;
display.setText("Your total is " + counter);
}
});
}
尝试运行时,我会遇到各种异常:
05-11 21:23:47.604: E/AndroidRuntime(1944): java.lang.RuntimeException: Unable to start activity ComponentInfo{l.r.thenewboston/l.r.thenewboston.StartingPoint}: java.lang.NullPointerException
05-11 21:23:47.604: E/AndroidRuntime(1944): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
这里怎么了
活动起点布局
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="l.r.thenewboston.StartingPoint"
tools:ignore="MergeRootFrame" />
<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="l.r.thenewboston.StartingPoint$PlaceholderFragment" >
<TextView
android:id="@+id/txt_display"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/total_text"
android:textSize="44sp"
android:layout_gravity="center"
android:gravity="center"/>
<Button
android:id="@+id/btn_add"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/txt_display"
android:layout_below="@+id/txt_display"
android:layout_marginTop="19dp"
android:textSize="18sp"
android:text="@string/add_one" />
<Button
android:id="@+id/btn_subscract"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/btn_add"
android:layout_alignBottom="@+id/btn_add"
android:layout_alignRight="@+id/txt_display"
android:text="@string/minus_one"
android:textSize="18sp" />
}放
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
之后
之前
setContentView(R.layout.activity_starting_point);
问题是您正试图从
活动
访问片段布局
中的视图
这是不可能的。您的活动布局
只有一个容器来容纳片段
。因此创建活动时应该只添加片段
将活动中的代码
onCreate
移动到片段
onCreateView
,如下所示
在片段布局充气后,您可以从onCreate视图中的占位符片段访问按钮和文本视图
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fregment_starting_point, container,false);
dd = (Button) rootView.findViewById(R.id.btn_add);
substract = (Button) rootView.findViewById(R.id.btn_subscract);
display = (TextView) rootView.findViewById(R.id.txt_display);
add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
counter++;
display.setText("Your total is " + counter);
}
});
return rootView;
}
粘贴存在空指针异常的代码行。很可能findViewById没有找到视图并返回一个空对象,但这只是一个猜测。发布活动\u起点
布局仍然会得到相同的结果这不起作用。在将Layout
设置为活动之前,他如何将Fragment
添加到R.id.container
中,但变量dd/substract/display不在此范围内(我已将静态fregment类添加到我的原始问题中)将它们移动到占位符Fragment
“无法从类型活动中对非静态方法findViewById(int)进行静态引用”是否使用rootView.findViewById
setContentView(R.layout.activity_starting_point);
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fregment_starting_point, container,false);
dd = (Button) rootView.findViewById(R.id.btn_add);
substract = (Button) rootView.findViewById(R.id.btn_subscract);
display = (TextView) rootView.findViewById(R.id.txt_display);
add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
counter++;
display.setText("Your total is " + counter);
}
});
return rootView;
}