How to align a button in Relative Layout Programmatically?

Question

I am trying to align a Button in a Relative Layout programmatically but the app is crashing every time i run with the above code. What am i doing wrong? I am facing the same problem with LayoutParams when i am trying to use margins.

Logcat

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="e.user.customcomponent.MainActivity"
    android:id="@+id/rLayout">
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/EditText" />
    <e.user.customcomponent.UIButton
        style="@style/UIButtonStyle.Action.Data" />
</RelativeLayout>

button_style.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <style name="UIButtonStyle">
        <item name="android:layout_width">wrap_content</item>
        <item name="android:layout_height">wrap_content</item>
        <item name="android:tag">UIButton</item>
        <item name="android:id">@id/UIButton</item>
        <item name="android:layout_below">@id/EditText</item>
        <item name="SetText">Save Data</item>
        <item name="SetRoundCorners">true</item>

        <item name="SetAlignCentre">true</item>

    </style>

    <item name="UIButton" type="id">UIButton</item>

</resources>

Added UIButton.java File

UIButton.java

package e.user.customcomponent;

import android.annotation.SuppressLint;
import android.content.ContentValues;
import android.content.Context;
import android.content.res.TypedArray;
import android.database.sqlite.SQLiteDatabase;
import android.graphics.Color;
import android.graphics.drawable.GradientDrawable;
import android.text.TextUtils;
import android.util.AttributeSet;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RelativeLayout;
import android.widget.Toast;

public class UIButton extends android.support.v7.widget.AppCompatButton {

    Button btn = findViewWithTag("UIButton");
    EditText editText = findViewById(R.id.et);
    DatabaseHandler db;
    SQLiteDatabase datab;
    final ContentValues cv = new ContentValues();

    public UIButton(Context context) {
        super(context);
    }

    @SuppressLint("ResourceType")
    public UIButton(final Context context, AttributeSet attrs) {
        super(context, attrs);

        TypedArray typedArray = context.obtainStyledAttributes(attrs,
                R.styleable.UIButton);
        int count = typedArray.getIndexCount();
        try {

            for (int i = 0; i < count; ++i) {

                int attr = typedArray.getIndex(i);
                // the attr corresponds to the title attribute
                if (attr == R.styleable.UIButton_SetText) {
                    String msg = typedArray.getString(attr);
                    btn.setText(msg);
                } else if(attr == R.styleable.UIButton_SetSubmitAction) {
                    boolean action = typedArray.getBoolean(attr,false);
                    if(action == true) {
                        btn.setOnClickListener(new View.OnClickListener() {
                            public void onClick(View v) {
                                Toast.makeText(getContext(),"Button Clicked!",Toast.LENGTH_LONG).show();
                            }
                        });
                    }

                } else if (attr == R.styleable.UIButton_SetRoundCorners) {
                    boolean roundCorners = typedArray.getBoolean(attr,false);
                    if(roundCorners == true) {
                        btn.setBackgroundResource(R.drawable.rounded_corners);
                        GradientDrawable drawable = (GradientDrawable) btn.getBackground();
                        drawable.setColor(Color.BLUE);
                    }
                } else if (attr == R.styleable.UIButton_SaveData) {
                    boolean saveData = typedArray.getBoolean(attr,false);
                    if(saveData == true) {
                        db = new DatabaseHandler(context,"DemoDB",null,1);
                        datab = db.getWritableDatabase();
                        btn.setOnClickListener(new View.OnClickListener() {

                            @Override
                            public void onClick(View v) {
                                // TODO Auto-generated method stub

                                cv.put("data",editText.getText().toString());

                                long id = datab.insert("demoTable",null,cv);

                                Toast.makeText(context,String.valueOf(id)+"Data Inserted!",Toast.LENGTH_LONG).show();

                            }
                        });
                    }
                } else if (attr == R.styleable.UIButton_SetAlignCentre) {
                    boolean setAlignCentre = typedArray.getBoolean(attr,false);
                    if(setAlignCen
                    tre == true) {
                        RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams) btn.getLayoutParams();
                        params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
                        btn.setLayoutParams(params);
                    }
                }
            }
        }
        finally {
            typedArray.recycle();
        }
    }

    public UIButton(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }
}

Answer 1

系统找不到您的自定义UTButton类，这就是其引发异常的原因，请确保在使用该视图时已声明正确的程序包

Answer 2

This xml coading is causing problem-:

<e.user.customcomponent.UIButton
            style="@style/UIButtonStyle.Action.Data" />

Check you are using same package name as that you have declared.

Answer 3

May be your button is not bound, so it caused the attempt to invoke the virtual method. Try to output what the current btn is null