Question

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View; 
import android.view.View.OnClickListener;
import android.widget.EditText;
import android.widget.ImageButton;

public class MainActivity extends Activity {

DataHandlerSignIn handler1;
ImageButton signin;
EditText etxt1,etxt2;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    etxt1=(EditText) findViewById(R.id.user);
    etxt2=(EditText) findViewById(R.id.pass);
    signin=(ImageButton) findViewById(R.id.signup);

    signin.setOnClickListener(new OnClickListener(){

        @Override
        public void onClick(View v) {

            Intent ii = new Intent(MainActivity.this,SignUp.class);
            startActivity(ii);

        }

    });

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}

}

堆栈跟踪是

 E/AndroidRuntime(1644): FATAL EXCEPTION: main
 E/AndroidRuntime(1644): java.lang.RuntimeException: Unable to start      activity ComponentInfo{simple.smile.my_dairy/simple.smile.my_dairy.SignUp}:   java.lang.NullPointerException
 E/AndroidRuntime(1644):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
 E/AndroidRuntime(1644):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
 E/AndroidRuntime(1644):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
 E/AndroidRuntime(1644):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
 E/AndroidRuntime(1644):    at android.os.Handler.dispatchMessage(Handler.java:99)
 E/AndroidRuntime(1644):    at android.os.Looper.loop(Looper.java:137)
 E/AndroidRuntime(1644):    at android.app.ActivityThread.main(ActivityThread.java:5039)
 E/AndroidRuntime(1644):    at java.lang.reflect.Method.invokeNative(Native Method)
 E/AndroidRuntime(1644):    at java.lang.reflect.Method.invoke(Method.java:511)
 E/AndroidRuntime(1644):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
 E/AndroidRuntime(1644):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
 E/AndroidRuntime(1644):    at dalvik.system.NativeStart.main(Native Method)
 E/AndroidRuntime(1644): Caused by: java.lang.NullPointerException
 E/AndroidRuntime(1644):    at simple.smile.my_dairy.SignUp.onCreate(SignUp.java:30)
 E/AndroidRuntime(1644):    at android.app.Activity.performCreate(Activity.java:5104)
 E/AndroidRuntime(1644):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
 E/AndroidRuntime(1644):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
 E/AndroidRuntime(1644):    ... 11 more

SignUp活动代码

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.Toast;

public class SignUp extends Activity {

ImageButton click;
DataHandlerSignIn handler;
EditText et1,et2,et3,et4,et5;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_sign_up);

        et1 = (EditText) findViewById(R.id.name12);
        et2 = (EditText) findViewById(R.id.age12);
        et3 = (EditText) findViewById(R.id.date12);
        et4 = (EditText) findViewById(R.id.passed12);
        et5 = (EditText) findViewById(R.id.repassed12);

    click.setOnClickListener(new OnClickListener(){

        @Override
        public void onClick(View v) {

            String name1=et1.getText().toString();
            String age1=et2.getText().toString();
            String dob1=et3.getText().toString();
            String password1=et4.getText().toString();
            String password2=et5.getText().toString();

            if(password1.equals(password2))
            {
            handler = new DataHandlerSignIn(getBaseContext());
            handler.open();
            long id = handler.insertData(name1, age1, dob1, password1);
            Toast.makeText(getBaseContext(), "Saved",1000).show();  
            handler.close();
            Intent hello = new Intent(SignUp.this,MainActivity.class);
            startActivity(hello);
            }   
            else
            {
                   Toast.makeText(getBaseContext(),"passwords donot match plzz try again",3000).show();
                   et1.setText("");
                   et2.setText("");
                   et3.setText("");
                   et4.setText("");
                   et5.setText("");
            }   




        }

    });   
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_sign_up, menu);
    return true;
}




 }

我尝试使用意图从一个页面转到另一个页面。但我没有成功。我想我已经使用了正确的语法。但为什么会发生错误。有人请告诉我它中的错误以及如何解决它。提前谢谢。

Answer 1

您永远不会初始化ImageButton：

click.setOnClickListener(new OnClickListener()...
// click is null, calling a method on it will cause a crash

您需要初始化上面的ImageButton click：

click = (ImageButton)findViewById(R.id.click);
click.setOnClickListener(new OnClickListener()...

Answer 2

为click活动初始化SignUp imageButton。

click =(ImageButton) findViewById(R.id.click);

on onCreate()

使用意图从一个页面转到另一个页面时出错

2 个答案: