Question

这是我第一次制作Android应用程序，我希望它可以重用于我稍后可能制作的任何其他应用程序。这就是为什么我想创建一个按钮类，动态地生成一个按钮而不使用XML。但是当我想要这样做时，当我在makeButton方法中使用“setContentView”方法时程序崩溃。

此外，当我将“makeButton”的内容粘贴到onCreate方法时，它会以某种方式工作。为什么它在onCreate方法中工作而不在“makeButton”方法中？

MainActivity.java

package mw.mobilepccommunication;

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.ScrollView;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ButtonService button = new ButtonService("test", 100, 100, 100, 100, this);
        button.makeButton();

        //Contents of makeButton.
        Button mButton = new Button(this);
        mButton.setText("test");
        setContentView(mButton);
    }

    @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);
    }
}

ButtonSerivce.java

package mw.mobilepccommunication;

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

public class ButtonService extends AppCompatActivity {

    private String mNameButton;
    private int mHeight;
    private int mWidth;
    private int mXBeginPoint;
    private int mYBeginPoint;

    private Button mButton;
    private Context mContext;


 public ButtonService(String aNameButton, int aHeight, int aWdith, int aXBeginPoint, int aYBeginPoint, Context aContext)
    {
        mNameButton = aNameButton;
        mHeight = aHeight;
        mWidth = aWdith;
        mXBeginPoint = aXBeginPoint;
        mYBeginPoint = aYBeginPoint;
        mContext = aContext;
    }

public void makeButton()
    {
        mButton = new Button(mContext);
        mButton.setText(mNameButton);
        setContentView(mButton); // <-- It fails here.
    }
}

Answer 1

您对过程和活动生命周期的理解是错误的。

当您的活动由Android系统创建时，它会遇到几个必需的steps。

活动生命周期中的第一次附加到Window。考虑setContentView方法

的源代码

public void More ...setContentView(View view, ViewGroup.LayoutParams params) {
       getWindow().setContentView(view, params); // retrieve attached window 
       initWindowDecorActionBar();
}

由于之前Acrivity没有附加到窗口，getWindow方法返回null。

这就是你的应用程序崩溃的原因

更新

如果您想向MainActivity添加按钮，请尝试执行类似

的操作

public class ButtonService{

    private String mNameButton;
    private int mHeight;
    private int mWidth;
    private int mXBeginPoint;
    private int mYBeginPoint;

    private Button mButton;
    private Activity mContext;


 public ButtonService(String aNameButton, int aHeight, int aWdith, int aXBeginPoint, int aYBeginPoint, Activity aContext)
    {
        mNameButton = aNameButton;
        mHeight = aHeight;
        mWidth = aWdith;
        mXBeginPoint = aXBeginPoint;
        mYBeginPoint = aYBeginPoint;
        mContext = aContext;
    }

public void makeButton()
    {
        mButton = new Button(mContext);
        mButton.setText(mNameButton);
        mContext.setContentView(mButton);
    }
}

如何在没有XML的情况下在其他类方法中动态设置按钮

1 个答案:

更新