Question

这是错误我得到..我有采访..你需要显示这个应用..但得到错误.. PLZ帮助..该应用程序运行一小时回流利...我试图把注销按钮主要活动是返回登录活动但丢失登录按钮功能本身......

01-18 11:59:14.938 7321-7321/info.androidhive.materialdesign E/AndroidRuntime: FATAL EXCEPTION: main
                                                                           Process: info.androidhive.materialdesign, PID: 7321
                                                                           java.lang.RuntimeException: Unable to start activity ComponentInfo{info.androidhive.materialdesign/info.androidhive.materialdesign.activity.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2373)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2435)
                                                                               at android.app.ActivityThread.access$900(ActivityThread.java:153)
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1324)
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                               at android.os.Looper.loop(Looper.java:135)
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5375)
                                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                                               at java.lang.reflect.Method.invoke(Method.java:372)
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
                                                                            Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                               at info.androidhive.materialdesign.activity.MainActivity.onClickButtonListener3(MainActivity.java:51)
                                                                               at info.androidhive.materialdesign.activity.MainActivity.onCreate(MainActivity.java:45)
                                                                               at android.app.Activity.performCreate(Activity.java:6865)
                                                                               at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2326)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2435) 
                                                                               at android.app.ActivityThread.access$900(ActivityThread.java:153) 
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1324) 
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                               at android.os.Looper.loop(Looper.java:135) 
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5375) 
                                                                               at java.lang.reflect.Method.invoke(Native Method) 
                                                                               at java.lang.reflect.Method.invoke(Method.java:372) 
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904) 
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)

这是我的Login.java

package info.androidhive.materialdesign.activity;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.content.Intent;
import android.widget.EditText;
import android.widget.Toast;

import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.common.api.GoogleApiClient;
import info.androidhive.materialdesign.R;
import info.androidhive.materialdesign.db.sqlitedb;

public class Login extends Activity {

sqlitedb sqlitehelper;
SQLiteDatabase db;

private static Button btn_login, btn_back;

EditText emailEditText, passwordEditText;

int i;
int flag;

private GoogleApiClient client;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    btn_login = (Button) findViewById(R.id.login_1);

    emailEditText = (EditText)findViewById(R.id.uemail);
    passwordEditText = (EditText)findViewById(R.id.upass);

    sqlitehelper = new sqlitedb(getApplicationContext());
    db = sqlitehelper.getWritableDatabase();

    onClickButtonListener1();
    onClickButtonListener2();
    btn_login.setClickable(true);

    client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}
public void onClickButtonListener1()
{
    btn_back = (Button)findViewById(R.id.back_1);
    btn_back.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    // Intent i = new Intent("info.androidhive.materialdesign.activity.Home");
                    // startActivity(i);
                    finish();
                }
            }
    );
}
public void onClickButtonListener2()
{
    btn_login = (Button) findViewById(R.id.login_1);
    btn_login.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    onLoginClick(v);
                }
            }
    );
}

public void onLoginClick(View v) {

    if (v.getId() == R.id.login_1)
    {
        String contactEmail = emailEditText.getText().toString();
        String contactPassword = passwordEditText.getText().toString();

        String password = sqlitehelper.getSingleEntry(contactEmail);

        if (contactPassword.equals(password))
        {
            Intent i = new Intent("info.androidhive.materialdesign.activity.MainActivity");
            startActivity(i);
            finish();

        }
        else
        {
            Toast temp = Toast.makeText(Login.this, "Email and password don't match", Toast.LENGTH_SHORT);
            temp.show();
        }
    }
}

}

Answer 1

您在onCreate()此处初始化登录按钮：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    btn_login = (Button) findViewById(R.id.login_1);

然后在此处调用再次初始化按钮的onClickButtonListener2();：

public void onClickButtonListener2()
{
    btn_login = (Button) findViewById(R.id.login_1);

所以就这样做：

在onClickButtonListener2();中调用此onCreate()方法并修改代码：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    btn_login = (Button) findViewById(R.id.login_1);

    emailEditText = (EditText)findViewById(R.id.uemail);
    passwordEditText = (EditText)findViewById(R.id.upass);

    sqlitehelper = new sqlitedb(getApplicationContext());
    db = sqlitehelper.getWritableDatabase();
    btn_login.setClickable(true);
    onClickButtonListener1();
    onClickButtonListener2();
    client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}

并将onClickButtonListener2();更改为：

public void onClickButtonListener2(){
    btn_login.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    String contactEmail = emailEditText.getText().toString();
                    String contactPassword = passwordEditText.getText().toString();
                    String password = sqlitehelper.getSingleEntry(contactEmail);
                    if (contactPassword.equals(password)){
                         Intent i = new Intent("info.androidhive.materialdesign.activity.MainActivity");
                         startActivity(i);
                         YourActivity.this.finish();
                    }else{
                         Toast temp = Toast.makeText(Login.this, "Email and password don't match", Toast.LENGTH_SHORT);
                         temp.show();
                    }
                }
            }
    );
}

希望它有所帮助!!!

无法在android中启动活动

1 个答案: