Question

我已经创建了一个按钮，它应该是当你点击它来打开一个新活动时，但是当我按下它时它什么也没做。

然后我发现mainfest.xml中有错误//如何解决它有谁可以帮助我？

这是Mainactivity.java

package com.example.android.quizapp;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class MainActivity extends AppCompatActivity {

    private FirebaseAuth mAuth;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_start);

        mAuth = FirebaseAuth.getInstance();
    }
    @Override
    public void onStart() {
        super.onStart();
        // Check if user is signed in (non-null) and update UI accordingly.
        FirebaseUser currentUser = mAuth.getCurrentUser();

        if (currentUser == null ){

            Intent startIntent = new Intent(MainActivity.this, StartActivity.class);
            startActivity(startIntent);
        }
    }
}

这是Startactivity.java

    package com.example.android.quizapp;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class StartActivity extends AppCompatActivity {

    private Button mRegBtn;
    public StartActivity(Intent startIntent) {

    }

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

        mRegBtn = (Button) findViewById(R.id.start_reg_button);

        mRegBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent reg_intent = new Intent(StartActivity.this, RegisterActivity.class);
                startActivity(reg_intent);
            }
        });
    }
}

这是Mainifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.android.quizapp">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".StartActivity" /> /**<<The Error is here**/
        <activity android:name=".RegisterActivity"></activity>
    </application>

</manifest>

Answer 1

从StartActivity中删除构造函数：

public StartActivity(Intent startIntent) {

}

Answer 2

    package com.example.android.quizapp;

    import android.content.Intent;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;

    import com.google.firebase.auth.FirebaseAuth;
    import com.google.firebase.auth.FirebaseUser;

    public class MainActivity extends AppCompatActivity {

        private FirebaseAuth mAuth;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_start);
            mAuth = FirebaseAuth.getInstance();
        }
        @Override
        public void onStart() {
            super.onStart();
            // Check if user is signed in (non-null) and update UI accordingly.
            FirebaseUser currentUser = mAuth.getCurrentUser();
            if (currentUser == null ) {
                Intent startIntent = new Intent(MainActivity.this, SecondActivity.class);
                startActivity(startIntent);
            }
        }
    }

第二单元：

package com.example.android.quizapp;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class SecondActivity extends AppCompatActivity {

    private Button mRegBtn;


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

        mRegBtn = (Button) findViewById(R.id.start_reg_button);

        mRegBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent reg_intent = new Intent(SecondActivity.this, RegisterActivity.class);
                startActivity(reg_intent);
            }
        });
    }
}

Answer 3

你有几个问题，但主要问题是new StartActivity(startIntent)尝试startActivity（startIntent）; startActivity是一个关键字。 Android已经有了这个名称的方法，所以你通过创建一个具有此名称的类来混淆自己。你不使用构造函数来启动活动使用意图回调将由android调用，因为每个可视组件（视图）都是测量，引用，绘制或其他任何东西（无论什么是黑盒子）。显式意图由类名调用，就像你在这里所做的那样清单是好的。如果没有破损，请不要修理它。

清单 - 具有活动的“没有默认构造函数”

3 个答案: