Java 当我想执行新任务时,我的android应用程序就会崩溃
嗨,伙计们,我是android新手,我想做一个应用程序,比如一个日常计划。 问题是,我的应用程序打开了,我有了新任务按钮,当我点击按钮添加新任务时,应用程序崩溃。我在论坛上搜索了类似的问题,但没有得到帮助 这是我的cat日志文件:Java 当我想执行新任务时,我的android应用程序就会崩溃,java,android,crash,nullpointerexception,Java,Android,Crash,Nullpointerexception,嗨,伙计们,我是android新手,我想做一个应用程序,比如一个日常计划。 问题是,我的应用程序打开了,我有了新任务按钮,当我点击按钮添加新任务时,应用程序崩溃。我在论坛上搜索了类似的问题,但没有得到帮助 这是我的cat日志文件: 09-27 19:03:46.035: D/dalvikvm(19346): Late-enabling CheckJNI 09-27 19:03:46.440: D/dalvikvm(19346): GC_FOR_ALLOC freed 136K, 4% free
09-27 19:03:46.035: D/dalvikvm(19346): Late-enabling CheckJNI
09-27 19:03:46.440: D/dalvikvm(19346): GC_FOR_ALLOC freed 136K, 4% free 12874K/13319K, paused 31ms
09-27 19:03:46.440: I/dalvikvm-heap(19346): Grow heap (frag case) to 13.127MB for 379472-byte allocation
09-27 19:03:46.465: D/dalvikvm(19346): GC_FOR_ALLOC freed 0K, 4% free 13245K/13703K, paused 20ms
09-27 19:03:46.535: D/AbsListView(19346): Get MotionRecognitionManager
09-27 19:03:49.510: D/CLIPBOARD(19346): Hide Clipboard dialog at Starting input: finished by someone else... !
09-27 19:03:53.625: D/AndroidRuntime(19346): Shutting down VM
09-27 19:03:53.625: W/dalvikvm(19346): threadid=1: thread exiting with uncaught exception (group=0x40c5d1f8)
09-27 19:03:53.635: E/AndroidRuntime(19346): FATAL EXCEPTION: main
09-27 19:03:53.635: E/AndroidRuntime(19346): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.dailyplanner/com.example.dailyplanner.new_task}: java.lang.NullPointerException
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1894)
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.app.ActivityThread.access$600(ActivityThread.java:128)
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.os.Handler.dispatchMessage(Handler.java:99)
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.os.Looper.loop(Looper.java:137)
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.app.ActivityThread.main(ActivityThread.java:4514)
09-27 19:03:53.635: E/AndroidRuntime(19346): at java.lang.reflect.Method.invokeNative(Native Method)
09-27 19:03:53.635: E/AndroidRuntime(19346): at java.lang.reflect.Method.invoke(Method.java:511)
09-27 19:03:53.635: E/AndroidRuntime(19346): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
09-27 19:03:53.635: E/AndroidRuntime(19346): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
09-27 19:03:53.635: E/AndroidRuntime(19346): at dalvik.system.NativeStart.main(Native Method)
09-27 19:03:53.635: E/AndroidRuntime(19346): Caused by: java.lang.NullPointerException
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.app.Activity.findViewById(Activity.java:1851)
09-27 19:03:53.635: E/AndroidRuntime(19346): at com.example.dailyplanner.new_task.<init>(new_task.java:19)
09-27 19:03:53.635: E/AndroidRuntime(19346): at java.lang.Class.newInstanceImpl(Native Method)
09-27 19:03:53.635: E/AndroidRuntime(19346): at java.lang.Class.newInstance(Class.java:1319)
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.app.Instrumentation.newActivity(Instrumentation.java:1027)
09-27 19:03:53.635: E/AndroidRuntime(19346): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1885)
09-27 19:03:53.635: E/AndroidRuntime(19346): ... 11 more
这是新的_task.java文件:
package com.example.dailyplanner;
import android.os.Bundle;
import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends ListActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//SQLiteDatabase db = openOrCreateDatabase("MyDB", MODE_PRIVATE, null );
//db.execSQL("CREATE TABLE IF NOT EXISTS Data1 (Id INT IDENTITY(1,1) NOT NULL, text VARCHAR, time TIME, date DATE)");
Button nTaskBtn = (Button) findViewById(R.id.nTask);
nTaskBtn.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Intent nTaskScreen = new Intent(getApplicationContext() , new_task.class);
startActivity(nTaskScreen);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
package com.example.dailyplanner;
import android.R.string;
import android.app.Activity;
import android.app.Dialog;
import android.app.TimePickerDialog;
import android.net.UrlQuerySanitizer.ValueSanitizer;
import android.os.Bundle;
import android.renderscript.Sampler.Value;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.TimePicker;
public class new_task extends Activity {
static final int TIME_DIALOG_ID=0;
final TextView timeText = (TextView) findViewById(R.id.timeTxt);
TextView dateText = (TextView) findViewById(R.id.dateTxt);
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.new_task);
Button btnSave = (Button) findViewById(R.id.btnSave);
btnSave.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
}
});
Button btnSetTime = (Button) findViewById(R.id.btnSetTime);
btnSetTime.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
showDialog(TIME_DIALOG_ID);
}
});
}
private TimePickerDialog.OnTimeSetListener mTimeSetListener = new TimePickerDialog.OnTimeSetListener() {
public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
timeText.setText(hourOfDay+":"+minute);
};
};
protected Dialog onCreateDialog(int id){
switch(id){
case TIME_DIALOG_ID:
return new TimePickerDialog(this, mTimeSetListener, 0, 0, true);
}
return null;
}
有什么帮助吗?只有在设置内容视图后才能使用findViewById。在访问变量之前对其进行空检查也很有用。最后,确保布局文件R.layout.new_任务包含id为timeTxt、dateTxt、btnSave的项 我重写了你的一些作品,给你一个例子来说明我的意思:
private TextView timeText;
private TextView dateText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.new_task);
timeText = (TextView) findViewById(R.id.timeTxt);
dateText = (TextView) findViewById(R.id.dateTxt);
Button btnSave = (Button) findViewById(R.id.btnSave);
if (btnSave != null) {
btnSave.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
}
});
} else {
Log.e("MyActivity", "btnSave was null :(");
}
}
在调用
setContentView()
之后,必须在onCreate()
中调用findViewById()
这有很多代码要看,你能试着把它缩小到问题所在吗?我知道这是很多代码,但这就是问题所在,我看不到我的代码中有任何错误,所以我可以缩小范围,从日志猫我可以说也可以查看NullPointerExection,但我对这是一个新手,我真的不知道我做错了什么:我不认为你需要导入android.R.string;行一旦删除该行并检查您是否在任何行上遇到任何错误,请尝试为我们提供一些帮助。尝试单击logcat错误,在一个或另一个点上,您将被移动到java文件,该文件可能是错误的主要点。尝试检查是否删除R.string行时未出现错误,尽管正如Samir在下面建议的那样,在new_任务活动中,将这些引用放入final TextView timeText=(TextView)findViewById(R.id.timeTxt);TextView dateText=(TextView)findViewById(R.id.dateTxt);在setContentView之后(R.layout.new_任务)代码>现在有一个错误时间选择器对话框函数,它表示无法解析timeText Hnx jimmyyy!:就是这样,我只需要在创建和使用findview之前删除时间文本和日期文本。。。在oncreate之后,这就成功了,顺便说一句,stnsave不是空的,它只是没有保存信息的代码,我稍后会添加它…thanx很多:)
private TextView timeText;
private TextView dateText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.new_task);
timeText = (TextView) findViewById(R.id.timeTxt);
dateText = (TextView) findViewById(R.id.dateTxt);
Button btnSave = (Button) findViewById(R.id.btnSave);
if (btnSave != null) {
btnSave.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
}
});
} else {
Log.e("MyActivity", "btnSave was null :(");
}
}