使用下面的简单代码时程序崩溃,因为它在安装后自动关闭
package com.zaki.thenewboston;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
int counter;
Button add,sub; //used to reference to xml view ids
TextView display; //used to reference to xml view ids
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
//zaki: this is to wait the R.layout.activity_main to load first other wise the program may crash
counter =0;
add = (Button) findViewById(R.id.bAdd);
// sub = (Button) findViewById(R.id.bSub);
display = (TextView) findViewById(R.id.tvDisplay);
add.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
counter ++;
display.setText("Your total is" + counter);
}
});
/*
sub.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
counter --;
display.setText("Your total is" + counter);
}
});*/
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, 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_main, container, false);
return rootView;
}
}
}
这是logcat: 我觉得有一个null返回,但为什么呢?我不知道原因。 我确定onCreateView中的问题
09-21 12:58:37.277: D/AndroidRuntime(1449): Shutting down VM
09-21 12:58:37.277: W/dalvikvm(1449): threadid=1: thread exiting with uncaught exception (group=0xb2a81ba8)
09-21 12:58:37.277: E/AndroidRuntime(1449): FATAL EXCEPTION: main
09-21 12:58:37.277: E/AndroidRuntime(1449): Process: com.zaki.thenewboston, PID: 1449
09-21 12:58:37.277: E/AndroidRuntime(1449): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.zaki.thenewboston/com.zaki.thenewboston.MainActivity}: java.lang.NullPointerException
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.app.ActivityThread.access$800(ActivityThread.java:135)
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.os.Handler.dispatchMessage(Handler.java:102)
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.os.Looper.loop(Looper.java:136)
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.app.ActivityThread.main(ActivityThread.java:5017)
09-21 12:58:37.277: E/AndroidRuntime(1449): at java.lang.reflect.Method.invokeNative(Native Method)
09-21 12:58:37.277: E/AndroidRuntime(1449): at java.lang.reflect.Method.invoke(Method.java:515)
09-21 12:58:37.277: E/AndroidRuntime(1449): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
09-21 12:58:37.277: E/AndroidRuntime(1449): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
09-21 12:58:37.277: E/AndroidRuntime(1449): at dalvik.system.NativeStart.main(Native Method)
09-21 12:58:37.277: E/AndroidRuntime(1449): Caused by: java.lang.NullPointerException
09-21 12:58:37.277: E/AndroidRuntime(1449): at com.zaki.thenewboston.MainActivity.onCreate(MainActivity.java:38)
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.app.Activity.performCreate(Activity.java:5231)
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
09-21 12:58:37.277: E/AndroidRuntime(1449): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
09-21 12:58:37.277: E/AndroidRuntime(1449): ... 11 more
文件Activity_main.xml在
之下 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.zaki.thenewboston.MainActivity"
tools:ignore="MergeRootFrame" />
,文件fragment_main.xml在
之下<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/LinearLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.zaki.thenewboston.MainActivity$PlaceholderFragment" >
<TextView
android:id="@+id/tvDisplay"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="@string/your_total_is" />
<Button
android:layout_width="240dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="@string/add_one"
android:textSize="20sp"
android:id="@+id/bAdd"
/>
<Button
android:layout_width="240dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="@string/subtract_one"
android:textSize="20sp"
android:id="@+id/bSub"
/>
</LinearLayout>
另请注意我改变了行
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
是
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_main);
并且问题仍然存在
答案 0 :(得分:0)
将其移至片段类
counter =0;
add = (Button) rootView.findViewById(R.id.bAdd);
display = (TextView) rootView.findViewById(R.id.tvDisplay);
add.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
counter ++;
display.setText("Your total is" + counter);
}
});
答案 1 :(得分:0)
我发现问题不仅仅在于将代码移动到PlaceholderFragment,因为我得到了一个新的 我发布的编译错误
还有以下代码
add = (Button) findViewById (R.id.bAdd);
sub = (Button) findViewById(R.id.bSub);
display = (TextView) findViewById(R.id.tvDisplay);
应转换为如下
add = (Button) rootView.findViewById (R.id.bAdd);
sub = (Button) rootView.findViewById(R.id.bSub);
display = (TextView) rootView.findViewById(R.id.tvDisplay);
我很欣赏对我所做的解释的评论