我是Android的编程新手,目前我正在学习它,当我运行这个应用程序时它就停止了。 这是我的Logcat ::
12-29 00:35:09.510 3582-3582/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.smartrix.learning4, PID: 3582
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.smartrix.learning4/com.smartrix.learning4.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:68)
at android.support.v7.app.AppCompatDelegateImplV7.<init>(AppCompatDelegateImplV7.java:145)
at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:28)
at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:41)
at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:29)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:186)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:170)
at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:502)
at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:174)
at com.smartrix.learning4.MainActivity.<init>(MainActivity.java:16)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
这是我的Main_Activity.java ::
package com.smartrix.learning4;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.support.v4.view.GestureDetectorCompat;
public class MainActivity extends AppCompatActivity implements GestureDetector.OnGestureListener,
GestureDetector.OnDoubleTapListener{
private GestureDetectorCompat GD;
private TextView UserText = (TextView)findViewById(R.id.Nametext);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Reference the XML code button with JAVA code button
Button button = (Button)findViewById(R.id.Center);
Button button2 = (Button)findViewById(R.id.Right);
Button button3 = (Button)findViewById(R.id.Left);
Button button4 = (Button)findViewById(R.id.Bottom);
Button button5 = (Button)findViewById(R.id.Top);
this.GD = new GestureDetectorCompat(this,this);
GD.setOnDoubleTapListener(this);
//adding listener event
button.setOnClickListener(
new Button.OnClickListener(){
public void onClick(View v){
UserText.setText("CENTER");
}
}
);
button.setOnLongClickListener(
new Button.OnLongClickListener(){
@Override
public boolean onLongClick(View v) {
UserText.setText("It's a Long Click");
return false;
}
}
);
button2.setOnClickListener(
new Button.OnClickListener(){
public void onClick(View v) {
UserText.setText("RIGHT");
}
}
);
button3.setOnClickListener(
new Button.OnClickListener(){
public void onClick(View v) {
UserText.setText("LEFT");
}
}
);
button4.setOnClickListener(
new Button.OnClickListener(){
public void onClick(View v) {
UserText.setText("BOTTOM");
}
}
);
button5.setOnClickListener(
new Button.OnClickListener(){
public void onClick(View v) {
UserText.setText("TOP");
}
}
);
}
@Override
public boolean onSingleTapConfirmed(MotionEvent e) {
UserText.setText("onSingleTapConfirmed");
return true;
}
@Override
public boolean onDoubleTap(MotionEvent e) {
UserText.setText("onDoubleTap");
return true;
}
@Override
public boolean onDoubleTapEvent(MotionEvent e) {
UserText.setText("onDoubleTapEvent");
return true;
}
@Override
public boolean onDown(MotionEvent e) {
UserText.setText("onDown");
return true;
}
@Override
public void onShowPress(MotionEvent e) {
UserText.setText("onShowPress");
}
@Override
public boolean onSingleTapUp(MotionEvent e) {
UserText.setText("onSingleTapUp");
return true;
}
@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
UserText.setText("onScroll");
return true;
}
@Override
public void onLongPress(MotionEvent e) {
UserText.setText("onLongPress");
}
@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
UserText.setText("onFling");
return true;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
this.GD.onTouchEvent(event);
return super.onTouchEvent(event);
}
}
如何找到“App停止工作”的原因? main_activity代码有问题吗? 我能做些什么来解决这个问题? 请帮帮我......
答案 0 :(得分:0)
在MainActivity完全初始化并准备好查看视图之前,将值分配给UserText。
这样做。
..
private TextView userText ; // declare here(this is your UserText)
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
userText = (TextView)findViewById(R.id.Nametext); //assign value here
..
}