对于我的一个学校项目,我正在使用Android Studio构建自己的应用程序。这将是我的第一个应用程序。我也是Android Studio的新手,刚刚开始学习Java。我用python构建了一些游戏。
由于我是Java和应用程序开发的新手,因此该应用程序非常基础。它为用户提供了数学规则和公式,可用于研究测试等。
我已经对这个问题进行了研究,我注意到每个人都有不同的代码,这就是为什么我很想知道我是否可以得到一些关于代码问题的答案。
当我尝试运行我的应用时,我目前仍然遇到此错误:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: mcshreker.learnthemalllta, PID: 2876
java.lang.RuntimeException: Unable to start activity ComponentInfo{mcshreker.learnthemalllta/mcshreker.learnthemalllta.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at mcshreker.learnthemalllta.MainActivity.onCreate(MainActivity.java:120)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
这是我的代码(MainActivity.Java):
package mcshreker.learnthemalllta;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import static mcshreker.learnthemalllta.R.layout.activity_main;
import static mcshreker.learnthemalllta.R.layout.activity_main3;
import static mcshreker.learnthemalllta.R.layout.content_main;
@SuppressWarnings("ALL")
public class MainActivity extends AppCompatActivity {
private Button button;
public Button button2;
private Button button4;
private Button button5;
public Button button3;
public Button button7;
private void init6(){
button = (Button)findViewById(R.id.button7);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent toy6 = new Intent(MainActivity.this,Main8Activity.class);
startActivity(toy6);
}
});
}
private void init5(){
button = (Button)findViewById(R.id.button3);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent toy5 = new Intent(MainActivity.this,Main7Activity.class);
startActivity(toy5);
}
});
}
private void init4(){
button = (Button)findViewById(R.id.button2);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent toy4 = new Intent(MainActivity.this,Main5Activity.class);
startActivity(toy4);
}
});
}
private void init3(){
button = (Button)findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent toy3 = new Intent(MainActivity.this,Main4Activity.class);
startActivity(toy3);
}
});
}
private void init2(){
button5 = (Button)findViewById(R.id.button5);
button5.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent toy2 = new Intent(MainActivity.this,Main3Activity.class);
startActivity(toy2);
}
});
}
private void init(){
button4 = (Button)findViewById(R.id.button4);
button4.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent toy = new Intent(MainActivity.this,Main2Activity.class);
startActivity(toy);
}
});
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
init();
init2();
init3();
init4();
init5();
init6();
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
答案 0 :(得分:1)
这可能不是确切的问题,但如果您确实阅读了错误,它会告诉您fab
为空,这表明您可能删除了应用程序中存在的浮动操作按钮。
尝试删除这部分代码:
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});