MainActivity
public class MainActivity extends Activity{
ImageView imgsettings;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
imgsettings = (ImageView) findViewById(R.id.imgviewsettings);
imgsettings.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, AppSettings.class);
startActivity(intent);
}
});
}
}
清单
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".AppSettings"
android:label="@string/title_activity_app_settings" >
</activity>
</application>
的AppSettings
package com.example.oldie;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class AppSettings extends Activity implements OnClickListener {
TextView lblkeyword, txtkeyword;
TextView lblnumber, txtnumber;
TextView lbladdress, txtaddress;
Button btnok;
String filename = "preferences.txt";
public static int count = 0;
private static String keyword = "";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lblkeyword = (TextView) findViewById(R.id.lblkeyword);
txtkeyword = (TextView) findViewById(R.id.txtkeyword);
lblnumber = (TextView) findViewById(R.id.lblnumber);
txtnumber = (TextView) findViewById(R.id.txtnumber);
lbladdress = (TextView) findViewById(R.id.lbladdress);
txtaddress = (TextView) findViewById(R.id.txtaddress);
btnok = (Button) findViewById(R.id.btnok);
btnok.setOnClickListener(this);
lblkeyword.setOnClickListener(this);
lblnumber.setOnClickListener(this);
lbladdress.setOnClickListener(this);
//metritis gia na emfanisei mono mia fora to minima
if(count==0){
Toast.makeText(getApplicationContext(), "Tab on the labels for more information", Toast.LENGTH_LONG).show();
count = count + 1;
}
updateUIFromFiles();
}
@Override
public void onClick(View v) {
switch(v.getId()){
case R.id.lblkeyword:
Toast.makeText(getApplicationContext(), "Set a keyword set that will trigger the SMS checker", Toast.LENGTH_SHORT).show();
break;
case R.id.lblnumber:
Toast.makeText(getApplicationContext(), "Set a number that the app will communicate in case of emmergency", Toast.LENGTH_SHORT).show();
break;
case R.id.lbladdress:
Toast.makeText(getApplicationContext(), "Set the home address\nex. Agias Lavras 19, Piraeus, Greece", Toast.LENGTH_SHORT).show();
break;
case R.id.btnok:
if((txtkeyword.getText().toString().equals("")) || (txtaddress.getText().toString().equals("")) ||(txtnumber.getText().toString().equals(""))){
Toast.makeText(this, "Please fill all the Text Fields.", Toast.LENGTH_SHORT).show();
}
else{
savePreferences();
keyword = txtkeyword.getText().toString();
finish();
}
break;
}
}
private void savePreferences() {
//thewrithike anagkaio na apothikeutoun ta stoixeia se ena arxeio gia na mi xathoun.
try{
OutputStreamWriter outfile = new OutputStreamWriter(openFileOutput(filename, 0));
outfile.write(txtkeyword.getText().toString() + "\n" + txtnumber.getText().toString() + "\n" + txtaddress.getText().toString());
outfile.close();
Toast.makeText(this, "The contents are saved in the file.", Toast.LENGTH_LONG).show();
}
catch(Throwable t) {
Toast.makeText(this, "Exception: "+t.toString(), Toast.LENGTH_LONG).show();
}
}
private void updateUIFromFiles() {
try {
InputStream infile = openFileInput(filename);
if (infile != null){
InputStreamReader tmp = new InputStreamReader(infile);
BufferedReader reader = new BufferedReader(tmp);
txtkeyword.setText(reader.readLine());
txtnumber.setText(reader.readLine());
txtaddress.setText(reader.readLine());
infile.close();
}
}
catch (java.io.FileNotFoundException e) {
// that's OK, we probably haven't created it yet
}
catch (Throwable t) {
Toast.makeText(this, "Exception: "+t.toString(), Toast.LENGTH_LONG).show();
}
}
public String GetMessage(){ //Methodos gia na parei to service to keyword.
return keyword;
}
}
问题是
06-19 22:17:03.789: E/AndroidRuntime(17204): FATAL EXCEPTION: main
06-19 22:17:03.789: E/AndroidRuntime(17204): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.oldie/com.example.oldie.AppSettings}: java.lang.NullPointerException
06-19 22:17:03.789: E/AndroidRuntime(17204): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
06-19 22:17:03.789: E/AndroidRuntime(17204): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
06-19 22:17:03.789: E/AndroidRuntime(17204): at android.app.ActivityThread.access$600(ActivityThread.java:127)
06-19 22:17:03.789: E/AndroidRuntime(17204): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
06-19 22:17:03.789: E/AndroidRuntime(17204): at android.os.Handler.dispatchMessage(Handler.java:99)
06-19 22:17:03.789: E/AndroidRuntime(17204): at android.os.Looper.loop(Looper.java:137)
06-19 22:17:03.789: E/AndroidRuntime(17204): at android.app.ActivityThread.main(ActivityThread.java:4441)
06-19 22:17:03.789: E/AndroidRuntime(17204): at java.lang.reflect.Method.invokeNative(Native Method)
06-19 22:17:03.789: E/AndroidRuntime(17204): at java.lang.reflect.Method.invoke(Method.java:511)
06-19 22:17:03.789: E/AndroidRuntime(17204): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-19 22:17:03.789: E/AndroidRuntime(17204): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-19 22:17:03.789: E/AndroidRuntime(17204): at dalvik.system.NativeStart.main(Native Method)
06-19 22:17:03.789: E/AndroidRuntime(17204): Caused by: java.lang.NullPointerException
06-19 22:17:03.789: E/AndroidRuntime(17204): at com.example.oldie.AppSettings.onCreate(AppSettings.java:39)
06-19 22:17:03.789: E/AndroidRuntime(17204): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-19 22:17:03.789: E/AndroidRuntime(17204): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
06-19 22:17:03.789: E/AndroidRuntime(17204): ... 11 more
Intent的代码根本不起作用。我的应用程序崩溃并结束。我在吃药以控制我的愤怒之前迈出了一步......我＆＃39;不知道什么是错的，意图不起作用。请帮帮我。
答案 0 :(得分：1)
在AppSettings活动中，您将内容视图设置为R.layout.activity_main。我猜不是你想要的。它可能没有您期望找到的TextView。查找它们的调用返回null，这会在您调用setOnClickListener（）时导致异常。
答案 1 :(得分：0)
如果没有logcat，我无法确定问题究竟是什么，但是您可以尝试以下方法：
1。）尝试在Intent构造函数中使用getApplicationContext（）而不是MyActivity.this。
2.）检查AppSettings类是否与MainActivity类位于同一个包中。
如果您发布相关的logcat，我会尝试提供更多帮助
答案 2 :(得分：0)
您在AppSettings活动中使用了错误的布局：
setContentView(R.layout.activity_main);
这与你的MainActivity相同，这可能不对。结果你在这里找不到按钮：
btnok = (Button) findViewById(R.id.btnok);
然后将为null，当您尝试在此处设置onClickListener时：
btnok.setOnClickListener(this);
你得到NullPointerException。