Android 登录页面

Question

我在android中写了这个小登录activity。应用程序启动时默认为第一个 activity 到运行。但是当我尝试在 phone 上启动该应用程序时，它就崩溃了。我不知道错误来自哪里。我运行在 eclipse 上使用它。没有错误出现。代码有问题吗？

  package com.example.ruralaid1;
    import android.app.Activity;
    import android.content.Intent;
    import android.os.Bundle;
    import android.view.Menu;
    import android.view.View;
    import android.view.View.OnClickListener;
    import android.widget.AutoCompleteTextView;
    import android.widget.Button;
    import android.widget.Toast;
    public class MainActivity extends Activity {

     String username=null,password=null;

     AutoCompleteTextView user = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView1);
     AutoCompleteTextView pwd = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView2);

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

            Button b1 = (Button)findViewById(R.id.button1);

            username = user.getText().toString();
            password =  pwd.getText().toString();

            b1.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {

                    if(username.equals("") || username.equals(null))
                            {
                                Toast.makeText(getBaseContext(), "Username can't be empty", Toast.LENGTH_LONG).show();
                            }
                    else if (pwd.equals("") || pwd.equals(null))
                    {
                        Toast.makeText(getBaseContext(), "Password can't be empty", Toast.LENGTH_LONG).show();
                    }
                    else
                    {
                        if(username.equals("admin") && password.equals("admin"))
                        {
                            Toast.makeText(getApplicationContext(), "Redirecting...",  Toast.LENGTH_SHORT).show();

                             Intent i = new Intent(getApplicationContext(), Menu.class);

                        Toast.makeText(getBaseContext(), "Login Successful", Toast.LENGTH_LONG).show();
                        }
                        else
                        {
                            Toast.makeText(getApplicationContext(), "Username and Password don't match",  Toast.LENGTH_SHORT).show();
                            user.setText(null);
                            pwd.setText(null);
                        }
                    }
                }
            });


        }

}

Answer 1

移动

AutoCompleteTextView user = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView1);
AutoCompleteTextView pwd = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView2);

在 onCreate(..) 之后 setContentView(R.layout.activity_main);

Answer 2

将这两行放在setContentView(R.layout.activity_main);

之后

AutoCompleteTextView user = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView1);
 AutoCompleteTextView pwd = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView2);

代码如下所示。

public class MainActivity extends Activity {

 String username=null,password=null;

 AutoCompleteTextView user;
 AutoCompleteTextView pwd;


 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        user = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView1);
        pwd = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView2);

        Button b1 = (Button)findViewById(R.id.button1);

        username = user.getText().toString();
        password =  pwd.getText().toString();

        b1.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {


                if(username.equals("") || username.equals(null))
                        {
                            Toast.makeText(getBaseContext(), "Username can't be empty", Toast.LENGTH_LONG).show();
                        }
                else if (pwd.equals("") || pwd.equals(null))
                {
                    Toast.makeText(getBaseContext(), "Password can't be empty", Toast.LENGTH_LONG).show();
                }
                else
                {
                    if(username.equals("admin") && password.equals("admin"))
                    {
                        Toast.makeText(getApplicationContext(), "Redirecting...",  Toast.LENGTH_SHORT).show();

                         Intent i = new Intent(getApplicationContext(), Menu.class);

                    Toast.makeText(getBaseContext(), "Login Successful", Toast.LENGTH_LONG).show();
                    }
                    else
                    {
                        Toast.makeText(getApplicationContext(), "Username and Password don't match",  Toast.LENGTH_SHORT).show();
                        user.setText(null);
                        pwd.setText(null);
                    }
                }
            }
        });
    }
}

Answer 3

在 setContentView() 之后设置以下代码行

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    AutoCompleteTextView user = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView1);
     AutoCompleteTextView pwd = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView2);


    Button b1 = (Button) findViewById(R.id.button1);

    username = user.getText().toString();
    password = pwd.getText().toString();

    b1.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {

            if (username.equals("") || username.equals(null)) {
                Toast.makeText(getBaseContext(), "Username can't be empty",
                        Toast.LENGTH_LONG).show();
            } else if (pwd.equals("") || pwd.equals(null)) {
                Toast.makeText(getBaseContext(), "Password can't be empty",
                        Toast.LENGTH_LONG).show();
            } else {
                if (username.equals("admin") && password.equals("admin")) {
                    Toast.makeText(getApplicationContext(),
                            "Redirecting...", Toast.LENGTH_SHORT).show();

                    Intent i = new Intent(getApplicationContext(),
                            Menu.class);

                    Toast.makeText(getBaseContext(), "Login Successful",
                            Toast.LENGTH_LONG).show();
                } else {
                    Toast.makeText(getApplicationContext(),
                            "Username and Password don't match",
                            Toast.LENGTH_SHORT).show();
                    user.setText(null);
                    pwd.setText(null);
                }
            }
        }
    });

}

Answer 4

代码会是这样

 package com.example.ruralaid1;

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

 public class MainActivity extends Activity {

String username = null, password = null;

AutoCompleteTextView user, pwd;
Button b1;

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


    user = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView1);
    pwd = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView2);
     b1 = (Button) findViewById(R.id.button1);

    username = user.getText().toString();
    password = pwd.getText().toString();

    b1.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {

            if (username.equals("") || username.equals(null)) {
                Toast.makeText(getBaseContext(), "Username can't be empty", Toast.LENGTH_LONG).show();
            } else if (pwd.equals("") || pwd.equals(null)) {
                Toast.makeText(getBaseContext(), "Password can't be empty", Toast.LENGTH_LONG).show();
            } else {
                if (username.equals("admin") && password.equals("admin")) {
                    Toast.makeText(getApplicationContext(), "Redirecting...", Toast.LENGTH_SHORT).show();

                    Intent i = new Intent(getApplicationContext(), Menu.class);

                    Toast.makeText(getBaseContext(), "Login Successful", Toast.LENGTH_LONG).show();
                } else {
                    Toast.makeText(getApplicationContext(), "Username and Password don't match", Toast.LENGTH_SHORT).show();
                    user.setText(null);
                    pwd.setText(null);
                }
            }
        }
    });


}

 }

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