Android根据设备屏幕尺寸调整大小

Question

I have the following code called in my Android application. When I run it on an old Samsung Dart (api < 13), I get a NullPointer exception as noted below.

Is there a particular reason the code is working for the four lines above it but not the line it is getting the NullPointer?

@SuppressLint("NewApi")
@SuppressWarnings("deprecation")
public void adjustSize() {
    int width, height;

    Display display = getWindowManager().getDefaultDisplay();
    if (android.os.Build.VERSION.SDK_INT >= 13) {
         Point size = new Point();
         display.getSize(size);
         width = size.x;
         height = size.y;
    } else {
        width = display.getWidth();  // deprecated
        height = display.getHeight();  // deprecated
    }

    ImageView counties = (ImageView) findViewById(R.id.btnCounties);
    ImageView members = (ImageView) findViewById(R.id.btnMembers);
    ImageView webLink = (ImageView) findViewById(R.id.btnWebLink);
    ImageView logo = (ImageView) findViewById(R.id.logo);

    // Calculate image sizes
    if (height > width) {
        counties.getLayoutParams().height = (int) (width / 2.5);
        counties.getLayoutParams().width = (int) (width / 2.5);
        members.getLayoutParams().height = (int) (width / 2.5);
        members.getLayoutParams().width = (int) (width / 2.5);

        webLink.getLayoutParams().height = (int) ((width / 2.4) / 3.5);  // Null pointer error 
        webLink.getLayoutParams().width = (int) (width / 2.4);
        logo.getLayoutParams().height = (int) (height / 6);
        logo.getLayoutParams().width = width;
    } else {
        counties.getLayoutParams().height = (int) (height / 2.5);
        counties.getLayoutParams().width = (int) (height / 2.5);
        members.getLayoutParams().height = (int) (height / 2.5);
        members.getLayoutParams().width = (int) (height / 2.5);
    }
}

Answer 1

Simply,

ImageView webLink = (ImageView) findViewById(R.id.btnWebLink);

webLink is null .

Check your layout xml: are you sure the name ( btnWebLink ) is correct? Are you sure you're loading the correct layout xml file?

Probabily you have the ImageView in one layout but Android is loading the layout for a specific screen size where there's no btnWebLink.

Have a breakpoint in that line and check if the variable webLink is null.

The null pointer exception comes the first time you try to use the variable.