Android Checkbox getchecked(CompoundButton.OnCheckedChangeListener(无按钮点击事件)) [英] Android Checkbox getchecked (CompoundButton.OnCheckedChangeListener (without button click event))
本文介绍了Android Checkbox getchecked(CompoundButton.OnCheckedChangeListener(无按钮点击事件))的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
这是我的MainActivity:
public class MainActivity extends ActionBarActivity implements CompoundButton.OnCheckedChangeListener {
复选框cb;
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getCheckBox();
/ *
cb =(CheckBox)super.findViewById(R.id.checkbox);
cb.setOnCheckedChangeListener(this);
* /
}
public void getCheckBox(){
cb =(CheckBox)super.findViewById(R.id.checkbox);
cb.setOnCheckedChangeListener(this);
}
@Override
public void onCheckedChanged(CompoundButton buttonView,boolean isChecked){
if(buttonView.getId()== R.id.checkBox){
TextView tv =(TextView)findViewById(R.id.textView);
tv.setText(buttonView.getText()。toString());
}
}
}
我的布局:
< RelativeLayout xmlns:android =http://schemas.android.com/apk/res/android
xmlns:tools =http://schemas.android.com/toolsandroid:layout_width =match_parent
android:layout_height =match_parentandroid:paddingLeft =@ dimen / activity_horizontal_margin
android:paddingRight =@ dimen / activity_horizontal_margin
android:paddingTop =@ dimen / activity_vertical_margin
android:paddingBottom =@ dimen / activity_vertical_margintools:context =。MainActivity >
< CheckBox
android:layout_width =wrap_content
android:layout_height =wrap_content
android:text =My One
android :id =@ + id / checkBox
android:layout_alignParentBottom =true
android:layout_alignParentLeft =true
android:layout_alignParentStart =true
android:layout_marginBottom =160dp/>
< CheckBox
android:layout_width =wrap_content
android:layout_height =wrap_content
android:text =My Two
android :id =@ + id / checkBox2
android:layout_alignTop =@ + id / checkBox
android:layout_alignParentLeft =true
android:layout_alignParentStart =true
android:layout_marginTop =40dp/>
< TextView
android:layout_width =wrap_content
android:layout_height =wrap_content
android:textAppearance =?android:attr / textAppearanceSmall
android:text =Small Text
android:id =@ + id / textView
android:layout_below =@ + id / radioGroup
android:layout_alignParentLeft = true
android:layout_alignParentStart =true
android:textSize =50dp/>
< / RelativeLayout>
我运行时遇到以下异常
02-20 15:55:28.130 2110-2110 / sqllistviewdemo.wptrafficanalyzer.in.radiobutton E / AndroidRuntime:FATAL EXCEPTION:main
过程:sqllistviewdemo.wptrafficanalyzer.in。 radiobutton,PID:2110
java.lang.RuntimeException:无法启动活动ComponentInfo {sqllistviewdemo.wptrafficanalyzer.in.radiobutton / sqllistviewdemo.wptrafficanalyzer.in.radiobutton.MainActivity}:java.lang.NullPointerException:尝试调用虚拟方法'void android.widget.CheckBox.setOnCheckedChangeListener(android.widget.CompoundButton $ OnCheckedChangeListener)'对一个空对象引用
在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
在android .app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
在android.app.ActivityThread.access $ 800(ActivityThread.java:144)
在android.app.ActivityThread $ H.handleMessage(ActivityThread。 java:1278)
在android.os.Handler.dispatchMessage(Handler.java:102)
在android.os.Looper.loop(Looper.java:135)
在android.app .ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by:java.lang.NullPointerException:尝试在空对象引用上调用虚方法void android.widget.CheckBox.setOnCheckedChangeListener(android.widget.CompoundButton $ OnCheckedChangeListener)
at sqllistviewdemo.wptrafficanalyzer.in .radiobutton.MainActivity.getCheckBox(MainActivity.java:34)
at sqllistviewdemo.wptrafficanalyzer.in.radiobutton.MainActivity.onCreate(MainActivity.java:27)
在android.app.Activity.performCreate(Activity .java:5933)
在android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
在android。 app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
在android.app.ActivityThread.access $ 800(ActivityThread.java:144)
在android.app.ActivityThread $ H.handleMessage(ActivityThread.java :1278)
在android.os.Handler.dispatchMessage(Handler.java:102)
在android.os.Looper.loop(Looper.java:135)
在android.app。 ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
你能指导我吗?
提前感谢:)
如果您不想使用按钮点击监听器, findViewById(R。 id.checkbox);在xml中,ID为时,
android:id =@ + id / checkBox
ID是区分大小写的,请检查您的大小写。基本上你的代码是通过ID获取一个视图,而不是找到它。因此,您的cb对象设置为null,您在此处抛出空指针。
cb.setOnCheckedChangeListener
Here is my MainActivity :
public class MainActivity extends ActionBarActivity implements CompoundButton.OnCheckedChangeListener {
CheckBox cb;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getCheckBox();
/*
cb = (CheckBox) super.findViewById(R.id.checkbox);
cb.setOnCheckedChangeListener(this);
*/
}
public void getCheckBox(){
cb = (CheckBox) super.findViewById(R.id.checkbox);
cb.setOnCheckedChangeListener(this);
}
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
if(buttonView.getId()==R.id.checkBox){
TextView tv = (TextView) findViewById(R.id.textView);
tv.setText(buttonView.getText().toString());
}
}
}
And here my layout :
<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:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="My One"
android:id="@+id/checkBox"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginBottom="160dp" />
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="My Two"
android:id="@+id/checkBox2"
android:layout_alignTop="@+id/checkBox"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="40dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceSmall"
android:text="Small Text"
android:id="@+id/textView"
android:layout_below="@+id/radioGroup"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:textSize="50dp" />
</RelativeLayout>
I get the following exceptions when i run
02-20 15:55:28.130 2110-2110/sqllistviewdemo.wptrafficanalyzer.in.radiobutton E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: sqllistviewdemo.wptrafficanalyzer.in.radiobutton, PID: 2110
java.lang.RuntimeException: Unable to start activity ComponentInfo{sqllistviewdemo.wptrafficanalyzer.in.radiobutton/sqllistviewdemo.wptrafficanalyzer.in.radiobutton.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.CheckBox.setOnCheckedChangeListener(android.widget.CompoundButton$OnCheckedChangeListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.CheckBox.setOnCheckedChangeListener(android.widget.CompoundButton$OnCheckedChangeListener)' on a null object reference
at sqllistviewdemo.wptrafficanalyzer.in.radiobutton.MainActivity.getCheckBox(MainActivity.java:34)
at sqllistviewdemo.wptrafficanalyzer.in.radiobutton.MainActivity.onCreate(MainActivity.java:27)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Can you please guide me ? how do you work with checkbox if you don't want to use a button click listener ?
Thanks a lot in advance :)
解决方案
You are fetching your CheckBox with
findViewById(R.id.checkbox);
when in the xml, the id is
android:id="@+id/checkBox"
The id is case sensitive so check your capitalization. Basically your code is fetching a view by ID and not finding it. Therefore your cb object is set to null and you throw a nullpointer here
cb.setOnCheckedChangeListener(this);
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