我正在为按钮创建setOnClickListener
。但它正在制造问题
当我在评论setOnClickListener部分时,代码运行顺畅
这是我的代码:
public class Sales extends ActionBarActivity {
Button btnBuy;
Button btnSell;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sales);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
btnBuy = (Button) findViewById(R.id.btn_buy);
btnSell = (Button) findViewById(R.id.btn_sell);
btnBuy.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(Sales.this, Buy.class);
startActivity(intent);
finish();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.sales, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_sales,
container, false);
return rootView;
}
}
}
我的activity_sales.xml是:
<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="com.example.tcshackathon.Sales"
tools:ignore="MergeRootFrame" />
我的fragment_sales.xml是:
<LinearLayout 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="com.example.tcshackathon.Sales$PlaceholderFragment" >
<Button android:id="@+id/btn_buy"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Buy Something"
android:layout_marginTop="30dip"
android:layout_gravity="center_horizontal"
/>
<Button android:id="@+id/btn_sell"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/btn_logout"
android:text="Sell Something"
android:layout_marginTop="30dip"
android:layout_gravity="center_horizontal"
/>
</LinearLayout>
StackTrace:
03-14 17:59:26.135: E/AndroidRuntime(15741): FATAL EXCEPTION: main
03-14 17:59:26.135: E/AndroidRuntime(15741): Process: com.example.tcshackathon, PID: 15741
03-14 17:59:26.135: E/AndroidRuntime(15741): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.tcshackathon/com.example.tcshackathon.Buy}: java.lang.NullPointerException
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269)
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.app.ActivityThread.access$800(ActivityThread.java:139)
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.os.Handler.dispatchMessage(Handler.java:102)
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.os.Looper.loop(Looper.java:136)
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.app.ActivityThread.main(ActivityThread.java:5102)
03-14 17:59:26.135: E/AndroidRuntime(15741): at java.lang.reflect.Method.invokeNative(Native Method)
03-14 17:59:26.135: E/AndroidRuntime(15741): at java.lang.reflect.Method.invoke(Method.java:515)
03-14 17:59:26.135: E/AndroidRuntime(15741): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
03-14 17:59:26.135: E/AndroidRuntime(15741): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
03-14 17:59:26.135: E/AndroidRuntime(15741): at dalvik.system.NativeStart.main(Native Method)
03-14 17:59:26.135: E/AndroidRuntime(15741): Caused by: java.lang.NullPointerException
03-14 17:59:26.135: E/AndroidRuntime(15741): at com.example.tcshackathon.Buy.onCreate(Buy.java:93)
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.app.Activity.performCreate(Activity.java:5248)
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
03-14 17:59:26.135: E/AndroidRuntime(15741): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2173)
03-14 17:59:26.135: E/AndroidRuntime(15741): ... 11 more
我收到Java.lang.NullPointerException。
有人可以告诉我它为什么会发生吗?
答案 0 :(得分:7)
在评论中,您说btn_buy
属于fragment_sales.xml
。因此,您需要在onCreateView
Fragment
中初始化按钮
Button btnBuy,btnSell;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_sales,
container, false);
btnBuy = (Button)rootView.findViewById(R.id.btn_buy);
btnSell = (Button)rootView.findViewById(R.id.btn_sell);
btnBuy.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(getActivity(), Buy.class);
startActivity(intent);
finish();
}
});
return rootView;
}
按钮不属于activity_sales.xml
。因此,初始化失败导致NullPointerException
。
编辑:
由于您已更新帖子,因此有NPE @ line 93 Buy.java
。修理它。现在发布的代码很好。
答案 1 :(得分:1)
btnBuy = (Button) findViewById(R.id.btn_buy);
btn_buy
不属于activity_sales.xml
,因此findViewById()
之后btnBuy值为空
答案 2 :(得分:1)
不确定但请尝试
btnBuy.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(Sales.this, Buy.class);
startActivity(intent);
finish();
}
});
将view.onclicklistener替换为onclicklistener
答案 3 :(得分:0)
请参阅此链接
http://www.vogella.com/tutorials/AndroidActionBar/article.html
您可以使用onOptionsItemSelected()方法进行buttonclick操作。
您可以遵循的另一种方法是:直接使用
android:onClick="@string/buy_click"
在您的XML中和在类中使用
public void buy_click(View v){
/ ...在这里做你的工作.. / }
我不知道这是否是一种好的编程方式。