问题描述
- Android自定义控件中为Button设置自定义监听器出现空指针。
-
Android自定义TopBar中给ImageButton设置自定义点击监听器,当点击ImageButton时在listener处出现NullPointerException。会出错的地方我在后面写了//TODO 。
请问为什么会出现listener没有被实例化的情况?
还有为什么在MainActivity中使用findViewById实例化TopBar也会出现不能实例化控件的情况?
IDE : Android Studio ;
Compile Sdk Version : API 23 ;
Build Tool Version : 23.0.1 ;
Min Sdk Version : API 15 ;
Target Sdk Version : API 19 ;
部分代码:
#MainActivity.java
public class MainActivity extends AppCompatActivity { private TopBar topBar; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // topBar = (TopBar) findViewById(R.id.topBar); //TODO 这样无法实例化topBar ??? topBar = new TopBar(getApplicationContext(), null); if (topBar == null) { Toast.makeText(MainActivity.this, "NULL", Toast.LENGTH_SHORT).show(); } topBar.setOnTopBarClickListener(new TopBar.OnClickListener() { @Override public void onLeftButtonClick() { Toast.makeText(MainActivity.this, "Left", Toast.LENGTH_SHORT).show(); } @Override public void onRightButtonClick() { Toast.makeText(MainActivity.this, "Right", Toast.LENGTH_SHORT).show(); } }); } }
#TopBar.java
public class TopBar extends RelativeLayout { private ImageButton ibtLeft; private ImageButton ibtRight; private TextView tvTitle; private OnClickListener listener; public interface OnClickListener { void onLeftButtonClick(); void onRightButtonClick(); } public void setOnTopBarClickListener(OnClickListener listener) { this.listener = listener; } public TopBar(Context context, AttributeSet attrs) { super(context); LayoutInflater.from(context).inflate(R.layout.layout_top_bar, this); ibtLeft = (ImageButton) findViewById(R.id.ibt_left); ibtRight = (ImageButton) findViewById(R.id.ibt_right); tvTitle = (TextView) findViewById(R.id.tv_title); ibtLeft.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Toast.makeText(getContext(), "leftButton", Toast.LENGTH_SHORT).show(); //Toast可以显示 // listener.onLeftButtonClick(); //TODO NullPointerException 为什么没有实例化listener? } }); ibtRight.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { listener.onRightButtonClick(); //TODO NullPointerException } }); } }
#logcat输出
10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: FATAL EXCEPTION: main 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: java.lang.NullPointerException 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at com.vder.puzzlegame.ui.TopBar$2.onClick(TopBar.java:55) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at android.view.View.performClick(View.java:4204) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:17355) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:725) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:92) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at android.os.Looper.loop(Looper.java:137) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5041) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:511) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 10-14 13:42:14.442 1366-1366/com.vder.puzzlegame E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method)
解决方案
构造方法不对,像这样,把三个全上才可以在Xml文件中使用
public MyView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// TODO Auto-generated constructor stub
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
}
public MyView(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
解决方案二:
你的_activity__main.xml_是怎么写的??自定义控件要加上包名 吧
解决方案三:
同楼上,有可能是你布局的自定义控件没指向到这个自定义控件的类。
时间: 2024-08-04 10:38:53