Android應用程序在運行時意外停止

Question

在模擬器中測試我的應用程序時（我正在使用Eclipse）它向我顯示「應用程序Counter（com.ian.counter）已意外停止，請重試。運行時。我搜索了一個答案，但我找不到答案。任何人都知道問題？

代碼：

package com.ian.counter; 

import android.app.Activity; 
import android.widget.TextView; 
import android.os.Bundle; 
import android.widget.Toast; 

public class CounterActivity extends Activity { 
    /** Called when the activity is first created. */ 
    TextView textView1 = (TextView) this.findViewById(R.id.textView1); 
    int count = 0; 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 
    } 

    public void Count(){ 
     count ++; 
     textView1.setText(Integer.toString(count)); 
    } 
} 

的logcat：

12-28 16:59:20.615: D/AndroidRuntime(353): Shutting down VM 
12-28 16:59:20.686: W/dalvikvm(353): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
12-28 16:59:20.756: E/AndroidRuntime(353): FATAL EXCEPTION: main 
12-28 16:59:20.756: E/AndroidRuntime(353): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.ian.counter/com.ian.counter.CounterActivity}: java.lang.NullPointerException 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569) 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.os.Handler.dispatchMessage(Handler.java:99) 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.os.Looper.loop(Looper.java:123) 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.app.ActivityThread.main(ActivityThread.java:3683) 
12-28 16:59:20.756: E/AndroidRuntime(353): at java.lang.reflect.Method.invokeNative(Native Method) 
12-28 16:59:20.756: E/AndroidRuntime(353): at java.lang.reflect.Method.invoke(Method.java:507) 
12-28 16:59:20.756: E/AndroidRuntime(353): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
12-28 16:59:20.756: E/AndroidRuntime(353): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
12-28 16:59:20.756: E/AndroidRuntime(353): at dalvik.system.NativeStart.main(Native Method) 
12-28 16:59:20.756: E/AndroidRuntime(353): Caused by: java.lang.NullPointerException 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.app.Activity.findViewById(Activity.java:1647) 
12-28 16:59:20.756: E/AndroidRuntime(353): at com.ian.counter.CounterActivity.<init>(CounterActivity.java:10) 
12-28 16:59:20.756: E/AndroidRuntime(353): at java.lang.Class.newInstanceImpl(Native Method) 
12-28 16:59:20.756: E/AndroidRuntime(353): at java.lang.Class.newInstance(Class.java:1409) 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.app.Instrumentation.newActivity(Instrumentation.java:1021) 
12-28 16:59:20.756: E/AndroidRuntime(353): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1561) 

任何幫助表示讚賞。

Answer 1

您正試圖在佈局設置之前設置textView1變量。您需要將其定義爲變量，然後在調用setContentView()之後將其指定爲onCreate()。就像這樣：

package com.ian.counter; 

import android.app.Activity; 
import android.widget.TextView; 
import android.os.Bundle; 
import android.widget.Toast; 

public class CounterActivity extends Activity { 
    /** Called when the activity is first created. */ 
    TextView textView1; 
    int count = 0; 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 
     textView1 = (TextView) this.findViewById(R.id.textView1); 
    } 

    public void Count(){ 
     count ++; 
     textView1.setText(Integer.toString(count)); 
    } 
} 

只需複製並粘貼以上，這會工作得很好。

Answer 2

你應該把這個線

textView1 = (TextView) this.findViewById(R.id.textView1);

後

setContentView(R.layout.main); 

，你只需要聲明的TextView在開始時

TextView textView1; 

不要嘗試使用findViewById(R.id.textView1);而declaraing實例變量因爲觀點並不如此在那個時間點。

Answer 3

這是你的代碼應該如何看起來像：

TextView textView1 = null; 
    int count = 0; 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 
    TextView textView1 = (TextView) findViewById(R.id.textView1); 
    } 

    public void Count(){ 
     count ++; 
     textView1.setText(Integer.toString(count)); 
    }